ABSTRACT Objective Anadromous salmonids undergo a preadaptive transformation to prepare for life at sea known as smoltification. Smoltification has been investigated since the 1830s, first to understand it as a physiological phenomenon and then to control it for the purposes of intensive aquaculture. Photoperiod manipulation is a well-established means of smoltifying some species, but diet-induced smoltification is an increasingly common, if less well researched, practice that demands greater attention. Methods Published literature and aquaculture industry practices were reviewed. Results Increasing day length is a potent cue for inducing smoltification, and photoperiod manipulation has been used to synchronize smoltification in salmon farming for decades. Certain seasonal changes in water chemistry may also serve as smoltification signals, and salmonids can detect these changes via calcium-sensing receptors (CaSRs). When appropriately stimulated by calcium, magnesium, or other ligands in the environment or in the feed, CaSRs prompt smoltification. Photoperiod manipulation is still widely used, but methods based on CaSR stimulation are now also commonly employed. Conclusion This review summarizes the state of knowledge regarding light- and diet-stimulated smoltification and methods for assessing smoltification status. Gaps in understanding and application of these strategies are addressed, along with future directions for the science and practice of controlled smoltification.
ABSTRACT Objective Microalgae have emerged as a promising source of potential natural feed alternative in aquaculture due to their high nutritional value and environmental benefits. Methods Microalgae like Chlorella vulgaris, Arthrospira platensis (also known as Spirulina platensis), Chlamydomonas, and Tribonema minus have been explored as marginal or supplementary feed items in aquatic organisms, highlighting their rich profile of vital elements, including lipids (especially omega-3), proteins, minerals, and vitamins. Incorporating microalgae (Chlorophyta, Rhodophyta, Euglenozoa, and Haptophyta) into aquatic animal diets enhances growth performance, boosts immunity, and reduces reliance on traditional feed sources. Results This review highlights the environmental benefits of microalgae cultivation, including carbon sequestration and wastewater treatment, and presents microalgae as a sustainable approach to mitigate aquaculture’s ecological impact in the long term. This review also examines challenges that are related to large-scale production, cost effectiveness, and variability in nutritional content, along with potential strategies to address these limitations. Conclusions Overall, this analysis highlights the significant contribution of microalgae to the advancement of sustainable aquaculture methods and identifies key areas for further investigation and improvement.
Objective Rocky Mountain Cutthroat Trout Oncorhynchus virginalis are valued in recreational fisheries. Efforts to culture these fish are impeded by the lack of diets formulated for Rocky Mountain Cutthroat Trout. The nutritional requirements of Rocky Mountain Cutthroat Trout are not completely known, leading to the use of Rainbow Trout O. mykiss diets that cause reduced growth performance in Rocky Mountain Cutthroat Trout. This study was conducted to determine the optimal dietary lysine requirement of cultured juvenile Snake River Cutthroat Trout O. virginalis behnkei.Methods Six diets were formulated using practical ingredients and purified amino acids to contain graded levels of lysine (1.81, 2.37, 2.90, 3.49, 4.03, and 4.61% on a dry matter basis). The diets were isonitrogenous, isolipidic, and isoenergetic on a dry matter basis. The essential amino acid profile of the diets matched the whole-body profile (except lysine) of Rocky Mountain Cutthroat Trout. Twenty-one 145-L tanks supplied with 15 degrees C spring water in a flow-through system were each stocked with 60 fingerlings (average body weight = 15.7 +/- 0.09 g) in a complete randomized design. Diets were hand fed to triplicate tanks of fish to apparent satiation three times daily for 10 weeks.Results Fish that were fed the lowest lysine level had significantly lower weight gain and daily growth index but had a higher feed conversion ratio than fish fed the other lysine levels. Fish that were fed diets with 2.90-4.61% lysine grew as well as fish fed the commercial control diet, with similar feed conversion ratios. Among several nonlinear regression models that were used to determine lysine requirements, the three-parameter logistic regression model provided the best fit to the daily growth index data (adjusted R2 = 0.804).Conclusions Optimal growth rates of juvenile Rocky Mountain Cutthroat Trout can be achieved with 2.37-2.90% total lysine in the diet. Lysine is an essential amino acid, and there is no known requirement in Rocky Mountain Cutthroat Trout. Our objective was to determine what the requirement is to improve the nutritional completeness of diets for Rocky Mountain Cutthroat Trout to enhance growth performance and nutrient retention. We recommend a minimum dietary lysine level of 2.9% for Rocky Mountain Cutthroat Trout.
Objectives: Ictavirus acipenseridallo2 (AciHV-2), White Sturgeon iridovirus (WSIV), Ranavirus rana1 (RR1), and Ranavirus alytes1 (RA1) are important viral pathogens of cultured sturgeon. The purpose of this study was to identify the virucidal efficacy of household bleach (free chlorine), a buffered povidone iodine complex (PVP iodine), and Virkon Aquatic, against these important sturgeon pathogens. Methods: The viruses were grown in White Sturgeon skin (AciHV-2 and RA1), White Sturgeon spleen (WSIV), or epithelioma papulosum cyprini (RR1) cell lines, and in vitro susceptibility to free-chlorine, PVP iodine, and Virkon Aquatic was investigated. Results: Virucidal reductions in titer >4 log10 TCID50/mL (>99.99% reduction) for AciHV-2 were obtained with 25 mg/L free chlorine after 10 min but immediately with 100 mg/L. Similarly, virucidal reductions for WSIV were obtained with 100 mg/L free chlorine immediately. Virucidal reductions for RA1 were obtained with 500 mg/L free chlorine, but RR1 persisted even after incubation with 500 mg/L free chlorine for 1 h. PVP iodine inactivated AciHV-2 after 30 min of incubation in 50 mg/L. White Sturgeon iridovirus was inactivated imme-diately after incubation in 50 mg/L PVP iodine. Although RA1 was inactivated after a 30-min incubation in 50 mg/L PVP iodine, RR1 isolates still persisted in 50 mg/L PVP iodine after 30 min. Among the disinfectants that were tested, Virkon Aquatic was the most consistent and effective, inactivating AciHV-2, WSIV, and the two ranaviruses immediately at the recommended concentration of 0.5%. Conclusion: The information presented in this study should be taken into consideration when developing bi-osecurity protocols in captive sturgeon programs to prevent the spread of these important viruses.
Objective Investigate the effects of salinity on the spawning of Channel Catfish Ictalurus punctatus broodstock in the saline waters of coastal Jiangsu, China.Methods The study established five salinity gradients (0, 1, 3, 5, and 7 parts per thousand) and systematically compared cumulative spawning rate, spawning time, spawn weight, and egg diameter under different salinity conditions. The broodstock were acclimatized to the target salinity for 24 h in fiber-reinforced plastic tanks before being transferred to the spawning cylinder. Males and females were allowed to spawn volitionally.Results Salinity substantially affected the spawning process. In the control group (0 parts per thousand) and low salinity groups (1 parts per thousand and 3 parts per thousand), the cumulative spawning rate ranged from 60% to 80% and days to spawn were completed within 1 week. At 5 parts per thousand salinity, the cumulative spawning rate remained 60%, while days to spawn extended to 7.5 +/- 5.9 d. When salinity increased to 7 parts per thousand, the cumulative spawning rate was only 40% and days to spawn reached 8.3 +/- 5.3 d. Egg masses exhibited gradual de-adhesion and loose morphology, eventually failing to maintain an intact matrix structure as salinity increased. Egg diameter significantly decreased and showed a significant negative correlation with salinity. Salinity showed a significant positive correlation with days to spawn and significant negative correlations with cumulative spawning rate and egg diameter.Conclusions Salinities at or below 3 parts per thousand have no adverse effects on Channel Catfish spawning, whereas salinities exceeding 5 parts per thousand severely inhibit reproductive performance. It is recommended that spawning farms for Channel Catfish be established in coastal Jiangsu waters with salinity <= 4 parts per thousand. These results provide guidance for local fry production, support the establishment of a complete industrial chain for Channel Catfish in Jiangsu, and contribute to the sustainable development of the industry. Salinity >= 5 parts per thousand delays spawning and suppresses the cumulative spawning rate of Channel Catfish. With increasing salinity, the egg masses exhibited increasingly obvious de-adhesion, with their morphology becoming loose until they could no longer maintain an intact matrix structure. The egg diameter also showed a significant progressive decrease.
Objectives Mannan, an antinutritional factor in plant-based aquafeeds, impedes nutrient absorption. How to reduce the antinutritional factors simply and efficiently in plant fish meal and improve its utilization is one of the difficulties in the current research. This study investigated the effects of dietary supplementation with beta-mannanase-producing Bacillus velezensis HF-14109 (HF-14109) in Common Carp Cyprinus carpio.Methods Juvenile Common Carp (35.2 +/- 0.5 g initial weight) were stocked in triplicate tanks (10 fish per tank) within a recirculating aquaculture system and fed one of four experimental diets (0, 107, 108, and 109 CFU/g HF-14109, respectively).Results Compared with the control group (0), the HF-14109 groups exhibited elevated digestive enzyme (beta-mannanase, lipase, and pepsin) activity in gut; increased final body weight, weight gain rate, specific growth rate, and antioxidant enzyme activities (glutathione, superoxide dismutase, catalase); and reduced malondialdehyde. Dietary beta-mannanase-HF-14109 significantly (1) elevated alkaline phosphatase, high-density lipoprotein, and lysozyme levels; (2) decreased aspartate aminotransferase, alanine aminotransferase, cholesterol, triglyceride, and pro-inflammatory cytokines (TNF-alpha, IL-1 beta, IL-6); and (3) enhanced anti-inflammatory markers (IL-10, TGF-beta). The inclusion of beta-mannanase-HF-14109 improved the intestinal morphology of Common Carp, including thickened walls and elongated villi; increased the relative abundance of Firmicutes, Bacteroidota, and Fusobacteria; and reduced the relative abundance of Proteobacteria relative to the control.Conclusions These findings highlight HF-14109 as a multifunctional probiotic for sustainable aquaculture. Bacillus velezensis HF-14109 isolated from the intestinal tract of Common Carp demonstrated beta-mannanase production and antibacterial activity. The HF-14109 increased intestinal villus length and wall thickness while modulating gut microbial composition, notably reducing pathogenic Aeromonas and enriching beneficial taxa.
Objective Bonefishes Albula spp. are economically important species in the recreational flats fishery and artisanal fisheries worldwide. Understanding the biology of bonefishes will help to preserve and manage these species, some of which are classified as "near threatened" by the International Union for Conservation of Nature.Methods We tested multiple hormonal maturational conditioning regimens under a compressed seasonal photothermal cycle using monthly doses of salmon pituitary extract at four levels (0, 80, 120, and 160 mg/kg of body weight) in Senegalese Bonefish A. goreensis females.Results All dosages except the sham (0 mg/kg) resulted in gonadal maturation. This led to two viable volitional spawns after induction with or without salmon gonadotropin-releasing hormone analog implants.Conclusions We used different methods to assess which females contributed to the two spawns, including analysis of monthly developmental patterns from fresh and preserved gonadal biopsies and genetic parentage analysis. In addition, an instance of the "pace-setting" response may have occurred, whereby salmon gonadotropin-releasing hormone analog-implanted females stimulated unimplanted females to spawn. The world's first controlled spawning of a bonefish species was demonstrated, showing that bonefish can be spawned in the laboratory without the deepwater habitats that they use in the wild. Hormones induced females to volitionally spawn with males in a tank, producing viable larvae.
Objective Salmon populations have been declining over the past several decades, and recent studies have found that hatchery-reared fish are returning to spawn as adults at a smaller size and at younger ages. Because of these declines and shifts in size and age at maturation, some spring Chinook Salmon Oncorhynchus tshawytscha hatcheries are struggling to reach their programmatic goals. This is compelling hatchery managers to rethink current rearing protocols. The goal of this investigation was to assess and compare the physiology and performance of fish reared under the standard protocol to those of fish reared under an alternative strategy.Methods A comparative study of juvenile spring Chinook Salmon was conducted at the Round Butte Hatchery/Pelton Ladder facility near Madras, Oregon, across five brood years. The standard rearing practice was compared to an alternative protocol, and we applied a unique experimental design whereby fish density (biomass per unit water volume) between the treatments was similar but the size of the individual fish and the number of fish per rearing vessel varied. The different rearing regimes yielded two treatments: (1) Big-Low: fish reared to a larger body size, with fewer fish per raceway (standard protocol) and (2) Small-High: fish reared to a smaller body size, with more individual fish per raceway (alternative protocol). Fish were evaluated for various prerelease (size, energetics, smolt development, and early male maturation) and postrelease (smolt out-migration travel time, adult returns to Bonneville Dam, and age at return) metrics.Results Prior to release, significant physiological differences between the Big-Low and Small-High treatments were observed for some smolt quality indicators (size, condition factor, and percent solid) but not all indicators (gill Na+, K+-ATPase). Despite these differences, the Small-High treatment did not appear to be physiologically compromised by being reared to a smaller body size with twice the number of fish. Postrelease travel time downstream to Bonneville Dam was faster for the Big-Low treatment. Proportionately, the standard production (Big-Low) treatment produced significantly more younger (age-2 and age-3) adult males, but returns were not significantly different for age-4 males and females compared to the alternative (Small-High) protocol. After adjusting for numbers of fish released, returns for all age-classes were higher in the Small-High treatment, suggesting that fish production goals could potentially be reached by rearing more small fish.Conclusions In this comparative hatchery-scale experiment, fish from the alternative rearing strategy generally outperformed fish from the standard hatchery practice. Given the unpredictability and influence of a variety of postrelease variables on survival, hatcheries may want to consider the trade-offs between altering fish size and/or fish abundance within the constraints of density (total biomass) limits for rearing vessels (tanks, raceways, etc.). This study highlights the benefits of periodically examining standard rearing practices to ensure that they are meeting desired hatchery performance goals and objectives. A hatchery-scale experiment was conducted to compare standard rearing practices to an alternative protocol. The alternative method of rearing larger numbers of small fish appears to improve hatchery production by yielding an increase in the number of fish returning as well as a more diverse adult age structure.
Objective To evaluate compound protein sources (CPSs) as a sustainable alternative to fish meal in diets for juvenile Japanese Seabass Lateolabrax japonicus, assessing impacts on growth performance and body composition. Methods A dietary CPS was formulated by blending soybean meal, meat and bone meal, peanut meal, and rapeseed meal (4:3:2:1 ratio), supplemented with crystalline L-methionine (0.77%), L-lysine (0.95%), and L-isoleucine (0.44%). Six isoenergetic diets with graded fish meal replacement (0, 13, 26, 39, 52, 65%) were prepared. Juvenile Japanese Seabass (n = 180 per group, initial weight 6.26 +/- 0.10 g) were reared in triplicate sea cages per diet and fed for 8 weeks. After 24-h fasting, fish were bulk-weighed per cage. Subsequently, 20 fish per replicate were euthanized with MS-222 (100 mg/L) and stored at -20 degrees C for whole-body composition analysis. Results The findings demonstrated that the replacement levels of 39, 52, and 65% were considerably lower than those of the other three groups (P < 0.05) in terms of weight gain, specific growth rate, and feed efficiency. Dietary CPS supplementation resulted in a decrease in whole-body crude protein and crude lipid and gross energy contents. The dietary CPS level had a substantial impact on whole-body lysine and methionine levels (P < 0.05), while other essential amino acid contents did not differ significantly. Conclusions A dietary CPS effectively replaces up to 26% of dietary fish meal without compromising production metrics, providing a viable strategy to enhance aquaculture sustainability.
Objective The marsh rams-horn Planorbella trivolvis and the ghost rams-horn Biomphalaria havanensis are intermediate hosts of the trematode Bolbophorus damnificus, which causes economic losses in the commercial catfish industry. Snail activity, survival, and egg laying and hatching are temperature dependent; thus, the timing of copper sulfate treatments can also influence efficacy of snail control. This study was conducted to determine the effects temperature on the survival, growth, and reproduction of these snails to improve the timing of copper sulfate treatments. Methods Four laboratory-reared adult snails were placed into each of 20 200-mL glass containers. Ten containers had adult marsh rams-horn and 10 containers had adult ghost rams-horn. Five containers of each species were maintained at 21 degrees C throughout the study. The other five containers of each species began at 21 degrees C, decreased to 5 degrees C, then increased to 51 degrees C (at 5 degrees C/week). Growth, mortality, and reproduction were monitored weekly. Results The risk of snail mortality was significantly higher when the treatment group was in the 31-51 degrees C range. Decreasing temperatures slowed growth, and increasing temperatures increased the growth of ghost rams-horn. Growth was stagnant for marsh rams-horn at all temperatures. Temperature had a significant effect on the spawning rate of both snail species. Decreasing temperatures slowed spawning, and increasing temperatures increased spawning to a peak at 31 degrees C (6.9 spawns/week) for ghost rams-horn and 21 degrees C (4.2 spawns/week) for marsh rams-horn. Spawning then decreased at temperatures that were above the respective peak temperatures. Conclusions Reactively responding to ponds that are infected with B. damnificus by treating snails in the summer with a uniform application of copper sulfate is risky because of the algicidal properties of copper and increased toxicity with increased temperatures. Based on the snail reproduction data from this study, peak reproduction occurs in the temperature range of 21-31 degrees C. Although treating all ponds proactively with copper may be financially prohibitive, it may be beneficial to proactively treat ponds with a history of trematode infections with multiple low doses of copper in the spring, thus targeting snails and eggs before populations have a chance to increase drastically.
Objectives Larval fish of many species lack fully developed digestive systems at the start of feeding and thus require diets that accommodate their limited digestive capacity. Larval culture of Walleye Sander vitreus is often characterized by low survival and variable growth performance, and diets tailored for their specific requirements are not available. This study assessed the use of protein hydrolysates derived from muscle tissue of nonnative carp species (Hypophthalmichthys spp.) generated using digestive enzymes from adult Walleye.Methods Two feeding trials tested the relative performance of hydrolyzed and intact carp-derived proteins as first-feed diets (from first exogenous feeding at 4 d posthatch to 34 d posthatch) and as weaning diets (transitioning from live brine shrimp Artemia spp. nauplii at 22-44 d posthatch). Survival, growth performance, feed acceptance, swim bladder inflation, and deformity rate were monitored and compared amongst treatments.Results In the first-feeding trial, Walleye fed the hydrolysate diet had significantly improved growth performance relative to those fed the intact protein diet, but survival did not differ significantly among treatments. In the weaning trial, growth performance and survival did not differ between hydrolyzed and intact diets, but both diets supported better growth than feeds with marine-derived hydrolyzed proteins. The best growth performance in both trials was achieved with a currently available commercial starter diet.Conclusions The improved growth performance of the hydrolyzed diet in the first-feeding trial highlights the importance of providing diets suitable for the limited gut capacity of Walleye larvae in early development (prior to 22 d posthatch). Given the lack of differences in growth performance during the weaning trials, digestive capacity requirements appear less important in later larval development. Although proteins derived from nonnative carp hydrolyzed using same-species digestive enzymes show promise in Walleye larval culture diets, further refinement is needed to match the performance of currently available commercial diets. This study also presents a novel approach utilizing muscle from nonnative species and byproducts from processing plants in the form of fish digestive tracts. This study tested the use of proteins from invasive carp that were broken down using adult Walleye enzymes in early-rearing Walleye diets. These hydrolyzed diets improved growth performance compared to nonhydrolyzed diets when used in first feeding but did not markedly improve growth or survival when used as weaning diets.
Objective: The Striped Bass Morone saxatilis is an emerging cultivar in the United States due in large part to its rapid growth rate and the ability to be reared in salinities ranging from freshwater to full-strength seawater. The successful culture of this species has been advanced by successive generations of selective breeding and domestication that have improved growth characteristics by around 8% per generation. Previous studies have shown that implementing reduced feeding protocols in aquaculture can have minimal impact on growth performance while potentially improving feed efficiency. Therefore, we evaluated the growth of fifth-generation, selectively bred pure-strain Striped Bass and determined whether reduced-frequency feeding might improve production efficiency of fish in recirculating aquaculture systems (RASs). Methods: We evaluated the production characteristics of F-5-generation domesticated Striped Bass that were cyclically fed either 3 d/week or 5 d/week in an RAS. Striped Bass fingerlings were stocked (n = 30 fish/tank) at an average body weight (BW) of 60 g and were fed a commercial diet to satiation once per feeding day. Sampling occurred at the beginning of the study (0 d poststocking [dps]) and then every 2-3 months (i.e., at 58, 113, 179, 262, and 351 dps). Results: We found that F-5-generation domesticated Striped Bass grew to market size (1.3 kg) in 11-12 months (18 months posthatch) when fed 5 d/week in an RAS. Within 179 dps, the mean BW of fish fed 5 d/week was significantly greater than that of fish fed 3 d/week, and this divergence in size persisted throughout the course of the study. Fish that were fed 3 d/week achieved a final BW (1.1 kg) that was 16% lower than the BW of fish fed 5 d/week, and they consumed 18% less feed overall. Although the specific growth rates of fish on the reduced-frequency feeding regime were lower initially, by 179 dps their growth had reached rates similar to those of fish fed 5 d/week. The final feed conversion ratio (FCR) was not significantly different between feeding regimes. However, the FCR changed with age: It was initially higher in smaller fish fed 3 d/week, whereas by the end of the study, the FCR had subsequently declined to a level at or below the FCR of fish fed 5 d/week. The shift in FCR occurred at a BW of around 785 g. Conclusions: Collectively, the results suggest that a shift to reduced-frequency feeding in larger fish (similar to 785 g) may have the potential to reduce feed and labor costs while minimizing impacts on growth and improving overall production efficiency of domesticated Striped Bass grown in RASs. This study demonstrates that F-5-generation, selectively bred Striped Bass can be grown rapidly (<12 months) in an RAS from 60 g to 1.3 kg, a size exceeding that of most domestically produced fish in the United States, which could allow for expansion of aquaculture to the high-value fillet market.
Objective Crappie Pomoxis spp., belonging to the family Centrarchidae, are among the most sought-after sport fish species in the United States. Crappie spawn during early spring in response to increasing photoperiod and water temperature, meaning that hatchery operators have limited time to capture and spawn broodstock. The ability to hold crappie for an extended time under prespawn conditions would allow for flexibility in scheduling spawning activities; however, the effects of prolonged holding on spawning efficiency and egg quality are not well understood.Methods Two studies were conducted to determine the effects of holding time under extended prespawn conditions (temperature = 13-15 degrees C) on the spawning efficiency of prespawn White Crappie P. annularis. Crappie were held in 5,000-L recirculating aquaculture systems for 6 and 8 weeks in year 1 (2023) and for 4 and 8 weeks in year 2 (2024), with 8 weeks chosen to coincide with the maximum duration of hatchery stocking practices. After holding in the 5,000-L tanks, broodstock were moved to smaller (450-L) tanks, where they were held for 2 weeks before spawning was induced by epaxial intramuscular injections of gonadotropin-releasing hormone analog (a 10% priming dose and then a 90% resolving dose 24 h later). Fish were strip-spawned upon ovulation.Results In year 1, 49% of females in the 6-week group ovulated, with a 54% fertilization rate; 47% of females in the 8-week group ovulated, with a significantly lower 12% fertilization rate. In year 2, 81% of females in the 4-week group ovulated, with a 52% fertilization rate; 93% of females in the 8-week group ovulated, with an 11% fertilization rate.Conclusions This study provides new insights into the extended holding potential and associated limitations for White Crappie spawning. Since key reproductive metrics, such as fecundity, remained stable over time, wild White Crappie broodstock can be maintained under prespawning conditions in recirculating aquaculture systems for up to 8 weeks. However, to maximize egg fertilization rates, the holding duration should be limited to 6 weeks. Fish hatcheries need flexibility when spawning fish. This study shows that crappie can be held in tanks before spawning, but keeping them too long (i.e., 8 weeks) reduces egg fertilization. These results help hatcheries to produce more and healthier fish.
Objective The objective of this study was to compare the zooplankton feeding habits of Channel Catfish Ictalurus punctatus and hybrid catfish (male Blue Catfish I. furcatus & times; female Channel Catfish).Methods This study used mesh cages to evaluate the zooplankton preferences and fish growth characteristics in situ. Three small, experimental ponds were prepared and fertilized based on typical industry practices. Two cages were deployed into each pond and stocked with 500 individual Channel Catfish or hybrid catfish fry. Twenty fish from each cage were sampled weekly for 9 weeks. At each sampling, the zooplankton community of the pond was sampled using a Wisconsin-style net and compared with that collected from the stomachs of the fish fry. Before dissection, the fish were measured for total length and gape length and weighed to follow relevant growth variables.Results The results indicated no significant differences in body characteristics based on fish species. However, the prey communities varied significantly. Cladocerans composed 44.3% of the pond zooplankton community but 52.0% of Channel Catfish diets; however, only 19.2% of hybrid catfish diets were attributed to cladocerans. Meanwhile, ostracods represented only 6.9% of the pond community but contributed 34.3% to the diet of hybrid catfish fry. Both fish species selected for smaller cladocerans from the true availability. This size bias was particularly evident in Moina, the most abundantly consumed cladoceran, where Channel Catfish and hybrid catfish selected for smaller individuals (471.1 +/- 12.3 & micro;m and 463.7 +/- 12.7 & micro;m, respectively) than the average size available in the pond (617.4 +/- 26.3 & micro;m).Conclusions Although hybrid catfish are credited with higher growth rates over the course of the entire food fish production cycle, the increase does not appear to be realized during the earliest stages of life, as total length and weight were similar between the two species in the present study. The increased prevalence of ostracods and lack of cladocerans in the diets of hybrid catfish fry may also hint at differences in their vertical distribution within the water column, relative to Channel Catfish fry. This study highlights the importance of providing the preferred prey groups and size-classes in supplementing manufactured feeds with zooplankton to maximize catfish production performance. Both Channel Catfish and hybrid catfish fry readily consume zooplankton. Channel Catfish consumed more cladocerans than hybrid catfish did; hybrid catfish consumed more ostracods than Channel Catfish did. These differences may indicate differences between the two species in their vertical distribution within the water column.
Objective Functional feed ingredients are dietary compounds that confer benefits beyond their nutritional value. Although they may contain some macro- and/or micronutrients, functional feed ingredients are intended to improve the health or well-being of farmed animals, particularly those that experience reduced environmental quality, increased infection pressure, or other challenging rearing conditions. The objective of this research was to determine whether dietary supplementation with a functional feed ingredient, ONE CURRENT, altered the performance and resilience of Rainbow Trout that were intensively reared in optimal or suboptimal conditions.Methods Juvenile Rainbow Trout Oncorhynchus mykiss (average initial weight = 36.6 +/- 0.7 g) were fed a commercially manufactured feed with (0.05%) or without (0.00%) supplementation of ONE CURRENT and reared for 8 weeks in first-use water in a serial reuse rearing system (phase 1) followed by an additional 8 weeks of rearing in third-use water (phase 2).Results Growth performance did not vary significantly during either phase of the trial, and weight gain, feed conversion ratio, specific growth rate, feed intake, and organosomatic indices were within expected ranges for juvenile Rainbow Trout reared under optimal or suboptimal conditions. Both feeds were readily accepted, and feeding behavior was aggressive throughout phase 1. Feeding was expectedly less active during phase 2, but the fish that received the ONE CURRENT-supplemented feed exhibited a significantly more robust feeding response during rearing in suboptimal conditions. Survival during phase 1 was nearly 100% in both groups (only a single mortality occurred), but mortality attributed to reduced environmental quality and gill hyperplasia steadily increased throughout phase 2. However, among fish that consumed the ONE CURRENT-supplemented feed, the onset was delayed and cumulative mortality was significantly lower (31% vs. 43%).Conclusions Dietary supplementation with ONE CURRENT had no adverse effects on the growth performance of juvenile Rainbow Trout under both optimal and suboptimal rearing conditions and may assist in maintaining performance and survival under challenging rearing conditions. Functional feed ingredients may improve the health and well-being of farmed fish. ONE CURRENT did not benefit Rainbow Trout that were reared in optimal conditions, but the fish that ate the supplemented feed exhibited a stronger feeding response and reduced mortality when they were exposed to suboptimal rearing conditions.
Objective Antibiotic resistance is a persistent concern for the global aquaculture industry. Monitoring trends in key bacterial species can help to preserve antibiotic effectiveness and sustain treatment success.Methods At Mississippi State University's Aquatic Research and Diagnostic Laboratory (ARDL) in Stoneville, Mississippi, the susceptibility of bacterial pathogens to approved antibiotics is estimated by disk diffusion assays. Susceptibility records, documented as zone of inhibition (ZOI) diameters (mm), along with antibiotic feed directives from the period 2007-2024, were assessed to monitor changes in the in vitro susceptibility of Edwardsiella ictaluri (the causative agent of enteric septicemia of catfish) and patterns of medicated feed use in the region. Susceptibility to florfenicol (FFC), oxytetracycline (OTC), and sulfadimethoxine-ormetoprim 5:1 is assessed for all case submissions to ARDL. According to ARDL standards, which are based on client feedback, isolates are considered susceptible (responsive) when the ZOI measures 20 mm or greater.Results In total, 3,911 diagnostic records were included in this retrospective, with mean ZOI diameters (+/- SD) for susceptible isolates measuring 47.98 mm (+/- 7.42) for FFC, 36.54 mm (+/- 7.79) for OTC, and 35.53 mm (+/- 6.23) for sulfadimethoxine-ormetoprim. For FFC, ZOI diameters were distributed bimodally, showing a population divide and potential epidemiological cutoff value above ARDL's clinical breakpoint of 20 mm. A high percentage (16.18% [625/3,870]) of isolates were unresponsive (ZOI = 0 mm) to OTC, which correlated to smaller FFC ZOIs. Data revealed a period spanning approximately 9 years (2014-2022) during which the prevalence of case isolates with reduced susceptibility to at least one antibiotic was elevated. This trend aligns with increased directed antibiotic use starting in 2013. After initiation of an experimental E. ictaluri vaccine program in 2019, there were marked reductions in antibiotic use in the region, which correlated with a return to baseline levels of susceptibility observed at ARDL.Conclusions This study demonstrates the impact of antibiotic use on susceptibility trends, highlighting the complex selective influences underlying the dynamics and instability of antimicrobial resistance within these bacterial populations and illustrating the potential to effectively combat antimicrobial resistance in aquaculture systems through vaccination and judicious antibiotic use. Diagnostic records indicate that increases in antibiotic prescriptions and antibiotic usage in the catfish industry were followed by a period of reduced in vitro responsiveness to antibiotics by isolates of Edwardsiella ictaluri. This was later followed by increased responsiveness when antibiotic use was limited.
Objective The Hogfish Lachnolaimus maximus is a species that is new to aquaculture. They are naturally found on the western side of the Atlantic ocean, mostly in tropical waters. Fishing pressure has led to population declines across most of their range in North America. The development and refinement of aquaculture protocols for early juvenile grow-out of Hogfish would lead to a better understanding of the feasibility of commercial production and stock enhancement.Methods Two dietetics experiments were conducted to evaluate the commercially available dry diets (brands: Otohime and Purina AquaMax) and associated feeding rates for juvenile Hogfish to determine a feeding regime for early grow-out of this new aquaculture species. The mean Hogfish starting weights for two grow-out experiments were 0.28 +/- 0.13 g (mean +/- standard deviation) and 1.31 +/- 0.88 g, respectively. The first experiment compared two commercially available diets that were fed at 6% body weight (BW)/d. A second experiment evaluated a single diet at feeding rates of 6% and 10% BW/d using the best performing diet from the first experiment.Results In the first experiment, significantly different values for final total length (4.41 +/- 0.92 cm vs. 4.05 +/- 0.77 cm [mean +/- standard deviation]) were observed between the diets. Weights increased from 0.28 +/- 0.13 g to 1.52 +/- 1.06 g versus 1.13 +/- 0.64 g but did not differ significantly between the diets. Survival between the fish that were fed with the two diets did not differ significantly at 68.5 +/- 12.1% versus 56.0 +/- 21.8%. In the second experiment, there were no significant differences in mean total length or weight and the fish grew from 1.31 +/- 0.88 g to 5.70 +/- 4.21 g. The survival rate of the fish that were fed 6% or 10% BW/d was identical (87.5%), indicating that a ration of 6% BW/d was sufficient.Conclusions Hogfish were able to be reared on commercially available diets from starting weights that were less than 0.5 g to final weights that were greater than 5 g, with survival rates that are promising for intensive production. This is the first published research evaluating feeding commercially available diets to early juvenile Hogfish. Juvenile hogfish were fed two similar diet types of two commercially available feed products to determine whether there would be any difference in growth. After one was determined to be the better feed option, that feed type was used at two feed rates. It was determined that the lower feed rate was just as good as the higher rate.
Objective The Delta Smelt Hypomesus transpacificus, an endangered species endemic to the San Francisco Estuary, faces a high risk of extinction due to habitat loss, water diversions, and changing environmental conditions. This study aimed to develop and validate the first sperm cryopreservation protocol for Delta Smelt as a tool to support conservation aquaculture, genetic banking, and reintroduction efforts.Methods Using captive fish maintained at University of California-Davis and Livingston Stone National Fish Hatchery, we conducted preliminary cryopreservation trials between 2020 and 2023. The finalized protocol employed 10% methanol as a cryoprotectant, a 1:15 sperm-to-extender dilution ratio, and a two-step freezing method using 0.25-mL French straws. Fertilization capacity was assessed in 2024 through two replicated trials comparing cryopreserved and fresh sperm. Fertilization success, expressed as eye-up rate, was statistically analyzed using a linear mixed-effects model.Results Fertilization rates varied across treatments, with cryopreserved sperm achieving eye-up rates ranging from 12% to 68% and fresh sperm from 17% to 76%. Despite variability in egg quality, cryopreserved sperm maintained an average relative eye-up rate of 83 +/- 7% compared with fresh controls, demonstrating consistent fertilization performance. Statistical analysis revealed no significant difference in fertilization success between treatments. Male and female fork lengths and their interaction also had no significant effect.Conclusions The cryopreservation protocol developed in this study effectively preserves Delta Smelt sperm fertilization capacity, demonstrating its reliability for conservation applications. This approach provides a foundational tool for genetic resource management and captive propagation of endangered estuarine fishes. A method was developed to freeze and store sperm from the endangered Delta Smelt. This approach is being used to preserve genetic material for future breeding and conservation, offering renewed hope for the recovery of this imperiled species.
Objective The Atlantic surfclam Spisula solidissima is a commercially valuable bivalve in the mid-Atlantic region of the United States. Although surfclam aquaculture is not yet widely practiced, it offers an opportunity to diversify surfclam products and expand production beyond traditional wild harvest methods. Although aquaculture farms are typically in protected coastal areas, farming surfclams in the open ocean offers the advantages of less competition for space, higher water quality, and natural habitat for the species. This study evaluates the feasibility of cultivating surfclams in federal waters offshore of New Jersey, USA.Methods Two experimental deployments were conducted in fall 2023 and spring 2024 of over 300,000 hatchery-reared seed-sized (15-mm shell length) surfclams. In cooperation with commercial partners, surfclams were deployed in large steel cages and contained within plastic mesh Hexcyls, often used on oyster longline farms. To determine the effects of stocking density on growth, surfclams were stocked at three densities ranging from 266 to 1,995 surfclams per Hexcyl in the fall and from 118 to 880 surfclams per Hexcyl in the spring.Results Growth rates (0.001-0.06 mm/day) that are comparable to those reported for wild populations in combination with high survival (approximate to 50% fall and 100% for fall and spring deployments, respectively) indicate that offshore aquaculture may be a viable method for commercial surfclam production, particularly for growing littleneck-sized surfclams (25-50-mm shell length).Conclusions Findings from this collaborative effort offer insight into the potential for offshore surfclam aquaculture using new grow-out areas with environmental conditions that are similar to those of the species' natural habitats. The possibility of farming Atlantic surfclams in the open ocean was investigated. Over 300,000 juvenile surfclams were deployed in specialized cages in federal waters in fall 2023 and spring 2024. High growth and survival rates suggest that this is a viable aquaculture method.
Objective This study aimed to determine the apparent digestibility coefficients for rendered animal protein ingredients fed to juvenile Ussuri Catfish Pseudobagrus ussuriensis.Methods Fourteen diets containing different feedstuffs were created by blending a control diet (70%) with each test ingredient (30%) and using 0.5% chromic oxide as an indicator.Results Results showed that protein peptide meal and white fish meal had higher gross energy, crude protein, and amino acid availability values, whereas horsemeat and bonemeal and pet-food-grade poultry by-product meal had lower dry matter, crude protein, and amino acid availability values. Enzymatically treated feather meal had relatively good apparent protein digestibility but led to a lower availability of lysine, histidine, methionine, and tryptophan.Conclusions White fish meal and protein peptide meal were optimal protein sources for Ussuri Catfish. Porcine blood plasma meal, porcine blood cell meal, feed-grade poultry by-product meal, poultry by-product meal from China, poultry by-product meal from America, whole-egg meal, and hydrolyzed chicken liver meal are potentially viable substitutes for fish meal. Enzymatically treated feather meal supplemented with amino acids could be a suitable protein source. Horsemeat and bonemeal and pet-food-grade poultry by-product meal were less favorable alternatives. Protein peptide meal and white fish meal were the optimal protein sources for Ussuri Catfish. Porcine blood plasma meal and hydrolyzed chicken liver meal showed potential as fish meal substitutes. Horsemeat and bonemeal and pet-food-grade poultry by-product meal were unsuitable as protein ingredients for this fish species.
