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.

Aquaculture feeds with optimum digestible starch levels can provide benefits but only through the continued identification and characterization of the available nutrient content of novel or lesser utilized starch sources for a larger variety of aquatic species. To address this literature gap, in vivo digestibility trials were conducted in rainbow trout and hybrid striped bass to determine the available nutrient content of commercially sourced U.S. grain sorghum hybrids. Based on digestibility data, a regression design was employed to test the replacement of wheat flour with U.S. grain sorghum in practical-type diets for rainbow trout and hybrid striped bass at four inclusion levels (0%, 5%, 10%, and 20%). All diets were formulated to contain 40% digestible protein and 18% crude lipid, and balanced to available lysine, methionine, threonine, and phosphorus to targets of 3.82, 1.30, 2.14, and 0.6, respectively, prior to cooking extrusion. For the growth trials, 10 rainbow trout (59.1 +/- 0.07 g, initial weight) or 10 hybrid striped bass (27.1 +/- 0.1 g) were randomly stocked into triplicate replicate tanks per diet (300 or 500 L, respectively) and fed for eight or nine weeks, respectively to assess effects on growth performance. No significant negative effects of U.S. grain sorghum inclusion on hybrid striped bass final fish weight, growth rate expressed as a percent increase, feed conversion ratio, feed intake, body condition indices, or whole-body proximate composition were observed. The effects of 20% red grain sorghum inclusion on rainbow trout final fish weight were explained by the linear model: . The reduced growth observed in rainbow trout at the 20% inclusion level underscores the need for additional research to examine the potential beneficial effects of further sorghum processing and optimize feed extrusion parameters when U.S. grain sorghum is used in place of wheat flour.

Abstract Lumpfish (Cyclopterus lumpus) are raised as cleaner fish for controlling sea lice. Intensive rearing is complicated by fin nipping that occurs between juvenile conspecifics. Lumpfish density‐dependent interactions are not well understood; therefore, the effects of rearing density for different fish size classes warranted evaluation. Two size classes (2‐ and 13‐g) of juvenile lumpfish were stocked at four different rearing densities (40, 60, 70, and 90 g/L) with growth, survival, and fish aggression assessed over 8 weeks. Mean weight gain and specific growth rates ranged from 170% to 307% and 1.77% to 2.50%, respectively, depending on density treatments, for the 2‐g fish, and from 286% to 471% and 2.42% to 3.10% for the 13‐g fish. Growth was negatively correlated with density, with faster growth linked to lower densities. No mortality occurred in any treatment and significant fish aggression only occurred among the larger lumpfish in the higher rearing densities. Based on these findings, growth of 2‐g lumpfish can be increased if reared at 40 g/L or slowed at 70 g/L without impacting aggression. For grow out of 13‐g fish to ~70 g with minimal aggression, a 40 g/L rearing density is recommended for faster growth and 60 g/L for slower growth.

A requisite to improving the taste and odor attributes of farmed fish is the availability of accurate and practical analytical methods to quantify 2-methylisoborneol (MIB) and geosmin (GSM). Solid-phase microextraction (SPME) enables reliable measurement of nanogram per liter quantities of MIB and GSM in water. In contrast, direct headspace (HS)-SPME of biological matrices with variable proximate compositions can increase bias and uncertainty in off-flavor determinations. Analytical recovery plays a crucial role in the accurate determination of MIB and GSM in fish, and this study investigates strategies to maximize and account for this recovery factor. MIB and GSM values in off-flavor catfish and trout were measured using direct HS-SPME and distillation as sample preparation techniques. Trout samples prepared by distillation yielded 10-fold higher GSM recoveries than those from direct HS-SPME (31% versus 3%). A stable isotope dilution method (SIDM) was implemented by routinely spiking samples with known quantities of deuterium-labeled MIB and GSM, allowing for the correction of sample-to-sample recovery deviations. SIDM-determined GSM values generated recoveries of 106 and 95% for direct HS-SPME and distilled trout, respectively. Aspects of the strategies and techniques presented can be incorporated into existing analytical methods to improve the accuracy and sample throughput. Particularly, routine inclusion of SIDM in the evaluation of MIB and GSM can facilitate identification of reliable practices to control off-flavors in aquaculture.

Geosmin is a primary source of muddy/earthy 'off-flavors' in farmed fish, which may render their organoleptic quality unacceptable to consumers. Model systems of geosmin uptake typically comprise exposure to waterborne geosmin that is absorbed via the gills. The present research demonstrates dietary exposure as an alternative route of geosmin uptake in Rainbow Trout (Oncorhynchus mykiss) fillets. Trout (average initial weight of 355 g) were stocked in quadruplicate compartmentalized raceways (N = 4 compartments per treatment, n = 50 fish per compartment) supplied with first-use, flow-through water (4.5 complete turnovers per hour). Fish were fed diets containing 0 (control dose), 0.005 (low dose), 0.05 (medium dose), or 0.5 (high dose) mg geosmin/kg feed at 1% body weight/day for four weeks. Fillets (12 fillets/diet/week plus 12 pre-trial fillet samples) and weekly feed and water samples were analyzed via GC-MS to determine geosmin concentrations. Feeding behavior was docu-mented daily according to a four-point scale. ANOVA with post-hoc Tukey tests and polynomial contrast, regression, correlation, and chi-squared statistical analyses were applied to data (alpha = 0.05 significance level). Palatability of feed did not hinder consumption of the geosmin-spiked feeds: although fish responded positively to all feeds, the most aggressive feeding behavior was observed among those fed medium and high dose feed. Geosmin was effectively imparted into fillets after one week, and no significant temporal effect was found after four weeks. Mean geosmin concentrations significantly increased in fillets from low (mean of 26 ng/kg geosmin) to medium (202 ng/kg) to high (441 ng/kg) dose feed groups during the trial. Polynomial contrasts and regression modeling validated this significant positive effect of dose on geosmin uptake, with an estimated 166 ng/kg rise in fillet-geosmin for every log10 increase in feed concentration. Waterborne geosmin levels immedi-ately post-feeding were conditionally independent of concentrations in feed and fillets, therefore dietary uptake was affirmed as the predominant mechanism of absorption in the present experimental system. Based on these findings, geosmin-spiked feeds may be used to induce predictable, repeatable levels of this off-flavor compound in fillets and serve as a model system for further investigation of sensory quality and off-flavor mitigation strategies for farm-raised fish.

While there is a growing need to increase farm fish production to meet food security needs of a growing population, humane slaughter treatments are not well understood. Use of sedative agents prior to slaughter can facilitate a more rapid and humane slaughter process. The present study was undertaken to evaluate the effects of implementing preslaughter electrosedation on the quality and consumer acceptance of farmed rainbow trout. A consumer sensory panel (n = 65) was conducted comparing rainbow trout slaughtered according to two methods: (1) immersion in an ice-water slurry (Control) or (2) immersion in an ice-water slurry immediately preceded by electrosedation (Electrosedation). Results from a sensory triangle test determined that there was no significant difference between the two fish harvested by different methods. These results suggest that electrosedation does not impact the sensory quality of farmed rainbow trout. This demonstrates that preslaughter electrosedation effectively aligns interests regarding animal welfare, efficiency, and product quality in the production of farm rainbow trout. This is an important finding as the results could provide insights for treating fish humanely without sacrificing the quality while meeting the demands of a highly regulated industry.

Infectious hematopoietic necrosis (IHN) is a significant viral disease affecting salmonids, whereas Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD), remains one of the most significant bacterial pathogens of salmonids. We explored maternal immunity in the context of IHN and BCWD management in rainbow trout (Oncorhynchus mykiss) aquaculture. Two experimental trials were conducted where different groups of female broodstock were immunized prior to spawning with an IHNV DNA vaccine or a live attenuated F. psychrophilum (Fp B.17-ILM) vaccine alone, or in combination. Progeny were challenged with either a low or high dose of IHNV at 13 days post hatch (dph) and 32 dph or challenged with F. psychrophilum at 13 dph. Mortality following a low-dose IHNV challenge at 13 dph was significantly lower in progeny from vaccinated broodstock vs. unvaccinated broodstock, but no significant differences were observed at 32 dph. Mortality due to BCWD was also significantly reduced in 13 dph fry that originated from broodstock immunized with the Fp B.17-ILM vaccine. After vaccination broodstock developed specific or neutralizing antibodies respectively to F. psychrophilum and IHNV; however, antibody titers in eggs and fry were undetectable. In the eggs and fry mRNA transcripts of the complement components C3 and C5 were detected at much higher levels in progeny from vaccinated broodstock and showed a significantly increased and rapid response post-challenge compared with unvaccinated broodstock. After challenges pro-inflammatory cytokine expression was immediately and considerably elevated in the fry from vaccinated broodstock vs. unvaccinated broodstock, whereas adaptive immune genes were elevated to a lesser degree. Results suggest that maternal transfer of innate and adaptive factors at the transcript level occurred because development of lymphomyeloid organs is not complete in such young fry. In addition to documenting maternally derived immunity in teleosts, this study demonstrates that broodstock vaccination can confer some degree of protection to progeny against viral and bacterial pathogens.

The aims of this review are to describe the role of 'blue-food production' (animals, plants and algae harvested from freshwater and marine environments) within a circular bioeconomy, discuss how such a framework can help the sustainability and resilience of aquaculture and to summarise key examples of novel nutrient sources that are emerging in the field of fed-aquaculture species. Aquaculture now provides >50% of the global seafood supply, a share that is expected to increase to at least 60% within the next decade. Aquaculture is an important tool for reducing resource consumption in global protein production and increasing resilience to climate change and other global disruptions (i.e. pandemics, geo-political instability). Importantly, blue foods also provide essential nutrition for a growing human population. Blue foods are helping to help the global goal of 'zero hunger' (United Nation's Sustainable Development Goal 2) while reducing the dependency on finite natural resources but further refinement and new solutions are needed to make the industry more 'circular' and sustainable, particularly with respect to sourcing raw materials for aquafeeds. This review describes the feed resources that are available or may be created within a circular bioeconomy framework, their role within the framework and in aquaculture and ultimately, how these resources contribute to de-risking and establishing a resilient aquaculture production chain.

The world population is increasing, and our current agricultural practices are not sustainable enough to address the concerns. Alternative proteins including plant-based proteins would provide a more sustainable source of food and feed ingredients. Among food systems, the aquaculture industry is rapidly growing, while still depending on marine sources as a main source of protein. Thus, using alternative plant-based proteins as a source for developing aquafeed would make this industry more viable. Sorghum is a valuable grain with high protein contents, proper mineral and fatty acids balance, and is available all around the world. However, sorghum has not been used widely for aquafeed development. In this review article, we cover sorghum production, composition, sorghum as a protein source for aquafeed development, and bioprocessing methods for enhancing the quality of sorghum.

A study involving duplicate experimental trials was conducted to determine whether differences in embryonic metabolic rate were associated with differences in growth performance, thermal tolerance, and expression of antimicrobial peptides (AMPs) in Rainbow Trout Oncorhynchus mykiss. Fertilized eggs were screened using a quantitative resazurin-based assay to identify those in the top and bottom 18% of observed metabolic rates for subsequent evaluation. After hatch and 14 (trial 1) or 10 (trial 2) weeks of rearing, no differences in survival (trial 1 = 93-95%; trial 2 = 96-97%), weight gain (trial 1 = 10,315-10,889%; trial 2 = 2,218-2,225%), specific growth rate (trial 1 = 4.74-4.79% body weight/d; trial 2 = 4.55-4.56% body weight/d), feed conversion ratio (trial 1 = 1.06; trial 2 = 0.85-0.86), feed intake (trial 1 = 10.89-11.23% body weight/d; trial 2 = 5.71-5.75% body weight/d), or critical thermal maxima (trial 1 = 26.8-27.0 degrees C; trial 2 = 28.3-28.5 degrees C) were observed between fish with high versus low embryonic metabolic rates. Beta defensins omDB-1, omDB-3, and omDB-4 were up-regulated in thermally challenged low-metabolic-rate fish, whereas these AMPs were down-regulated in high-metabolic-rate fish. Our results indicate that embryonic metabolic rate is not a useful metric for predicting juvenile survival, growth performance, or thermal tolerance of domesticated Rainbow Trout, though there may be a relationship between metabolic rate and AMP expression.

Understanding fatty acid requirements in multiple taxa is necessary to determine the degree to which dietary fish oil can be reduced or replaced with less costly, more abundant lipid sources. The polyunsaturated fatty acid (PUFA) requirements of hybrid Striped Bass (White Bass Morone chrysops x Striped Bass M. saxatilis) are currently reported as 0.5-1.0% eicosapentaenoic acid (20:5n-3) and/or docosahexaenoic acid (22:6n-3). This requirement does not account for n-3 PUFA essentiality on an individual fatty acid basis and does not address possible requirements for n-6 PUFAs (i.e., linoleic acid [18:2n-6] or arachidonic acid [20:4n-6]). Accordingly, hybrid Striped Bass were fed diets containing selected individual n-3 and n-6 C-18 PUFAs, n-3 and n-6 long-chain (LC) PUFAs, or combinations thereof to determine the essentiality or expendability of these nutrients. These experimental feeds were compared to feeds containing only saturated fatty acids (negative control) or menhaden fish oil (positive control). Growth performance and ratios of 22:5n-6 : 22:6n-3 observed in tissue fatty acid profiles suggested that dietary provision of 22:6n-3 was adequate to satisfy physiological demand for LC-PUFAs. However, reductions in feed conversion ratio and numeric improvements in growth suggest that dietary provision of 20:4n-6 is also important. Results of this study indicate that provision of C-18 PUFAs alone is insufficient to avoid essential fatty acid deficiency and to support optimal growth of this fish. To ensure that essential fatty acid requirements are met and performance is optimized, diets for hybrid Striped Bass should be formulated to contain 22:6n-3 and 20:4n-6, if not a full complement of n-3 and n-6 LC-PUFAs.

Invasive bigheaded carps, genus Hypophthalmichthys, are spreading throughout the Mississippi River basin. To explore the efficacy of a consumer-based market (i.e., invasivorism) to manage them, we developed a conceptual model and evaluated three harvest approaches-direct contracted removal, volume-based incentives ("fisher-side" control), and set-quota harvest ("market-side" control). We quantified the efficacy of these approaches and potential population impact in the Illinois River. Contracted removal was effective for suppressing small populations at the edge of the range but cannot support a market. "Fisher-side" removals totaled 225,372 kg in one year. However, participation was low, perhaps due to reporting requirements for fishers. The "market-side", set-quota approach removed >1.3 million kg of bigheaded carp in less than 6 months. Larger, older fish were disproportionately harvested, which may hinder the ability to suppress population growth. Total density declined in one river reach, and harvest may reduce upstream movement toward the invasion fronts. With sufficient market demand, harvest may control bigheaded carp. However, lack of processing infrastructure and supply chain bottlenecks could constrain harvest, particularly at low commodity prices. Given the geographical scale of this invasion and complicated harvest logistics, concerns about economic dependence on invasivorism that encourage stock enhancement are likely unmerited.

Rearing density is recognized as a critical consideration in fish husbandry: whereas higher densities may increase productivity and reduce production costs, they also represent a potential source of chronic stress and may negatively affect growth performance and product quality. Accordingly, we investigated the effects of rearing density on growth, physiological responses, and flesh quality of cobia (Rachycentron canadum). Fish (46.32 +/- 0.22 g, mean +/- SEM) were reared for 42 days in a low salinity (17.6 g/L) recirculation system according to treatments designated as low density (5 fish/tank, 3.30 +/- 0.02 kg/m(3)), medium density (10 fish/tank, 6.67 +/- 0.03 kg/m(3)), or high density (20 fish/tank, 13.15 +/- 0.16 kg/m(3)). Weight gain and specific growth rate were significantly higher among fish reared at low density; however, feed intake, feed conversion ratio, hepatosomatic index, condition factor, and dress-out were equivalent among treatments. Plasma cortisol, lactate, and osmolality levels were not affected by rearing density, and values were within basal ranges reported for juvenile cobia. Fillet drip-loss did not vary among treatments, but rigor mortis developed more rapidly among fish reared at high density. Rearing juvenile cobia at high densities may reduce growth performance and may influence the timing of rigor development.

Defining nutritional fatty acid essentiality in fish nutrition is complex given the wide range of taxonomic (e.g., divergence among species subjected to different selective pressures), biological (e.g., trophic levels and environmental tolerances), and external (e.g., experimental conditions and differences in feed formulation and manufacturing) factors involved, all of which can influence absolute requirements. Fishes vary in their ability to meet the physiological demand for long-chain (LC) polyunsaturated fatty acids (PUFAs; i.e., 20:4[n-6], 20:5[n-3], and 22:6[n-3]) via elongation and desaturation of C-18 PUFA (i.e., 18:2[n-6] and 18:3[n-3]) precursors. Previous attempts to generalize dietary fatty acid requirements have been focused on thermal and salinity preferences, suggesting-in many cases inaccurately-that coldwater and/or marine fish exhibit dietary requirements for LC-PUFAs but warmwater and/or freshwater species do not. Here, we provide a review of the current literature on the subject of dietary fatty acid essentiality in fish and introduce the experiments that form the basis of this special section. In these experiments, we tested the nutritional essentiality of C-18 PUFAs versus LC-PUFAs in feeds for five finfish relevant to intensive aquaculture: Rainbow Trout Oncorhynchus mykiss, Channel Catfish Ictalurus punctatus, Nile Tilapia Oreochromis niloticus, Florida Pompano Trachinotus carolinus, and hybrid Striped Bass (White Bass Morone chrysops x Striped Bass M. saxatilis), hypothesizing that the nutritional essentiality of C-18 PUFAs versus LC-PUFAs would be determined by trophic level. The findings collectively suggest that trophic level is the most reliable predictor of C-18 PUFA versus LC-PUFA nutritional essentiality in fish.

We evaluated the growth performance and fatty acid composition of juvenile Florida Pompano Trachinotus carolinus that were fed diets containing different combinations of n-3 and n-6 polyunsaturated fatty acids (PUFAs) to assess the relative importance of C-18 PUFAs and long-chain (LC) PUFAs in meeting the essential fatty acid requirements of this species. Juvenile fish (mean +/- SD =47.4 +/- 0.6 g/fish) were fed diets containing different combinations of n-3 and n-6 PUFAs: a positive control containing menhaden fish oil, a negative control containing hydrogenated soybean oil, and experimental diets containing hydrogenated soybean oil amended with ethyl esters of 18:3(n-3); 18:3(n-3) and 18:2(n-6); 22:6(n-3); 22:6(n-3) and 20:4(n-6); or 20:5(n-3), 22:6(n-3), and 20:4(n-6). After 7 weeks, weight gain, feed conversion ratio, and specific growth rate were significantly greater among fish that were fed the positive control feed in comparison with those that received the negative control feed. The addition of n-3 and/or n-6 PUFAs to the negative control formulation did not significantly improve performance in any case, although numeric improvements observed for weight gain and feed conversion ratio appeared to suggest some advantage from providing a complement of both n-3 and n-6 LC-PUFAs in the diet. Fatty acid composition varied significantly between all tissues, generally reflecting dietary fatty acid profiles. Tissue fatty acid profiles suggest that Florida Pompano have some ability to elongate and desaturate fatty acids and may be able to survive on diets containing C-18 PUFAs, but they perform optimally when provided with LC-PUFAs directly.

The American Fisheries Society (AFS) was founded during the early days of North American fish propagation, when pioneering fish culturists first began to coax food and fishing opportunities from pails of eggs and wriggling fry. In the absence of effective regulations and the will to enforce measures to prevent overfishing and habitat loss, fisheries professionals looked to hatcheries to fully address the problem of fisheries in decline. In the intervening decades, it became clear that hatcheries were not a panacea, but could be an effective tool for both enhancement and recovery. Fish culture has been practiced in North America for well over 150 years. Thanks partly to AFS and its members, why and how we propagate fish has changed dramatically during that time. In this piece, we briefly recount the history of North American fish culture, how AFS has influenced our understanding and use of hatcheries and hatchery‐origin fish, and provide a glimpse of what transformations may yet await fish culturists.