The majority of solids in intensive culture systems are from uneaten feed and fecal solids. The settling velocity of feeds and fecal solids is needed for the design of settling basins and modeling of the impacts of netpens. The UFT column developed in Germany in the 1980s has become the dominant column type for wastewater settling testing. The primary advantage of this column compared to conventional columns is the preconcentration of the settleable solids, elimination of problems with time zero estimates, and reduced sampling requirements. The conventional settling velocity analysis presented in standard references, while theoretically correct, and is virtually impossible to apply to actual fecal waste because of uncertainty in numbers, mass, shape, density, and drag characteristics. In addition, this analysis is unneeded, as the removal efficiency is measured directly in the settling column tests. Because the UFT column uses only the settleable solid portion of the total suspended solids, the settling results will depend on the preconcentration process. If this process misses a significant portion of the settleable solids, the resulting settling tests will overestimate the removal efficiency. If the ratio of non-settleable solids/total suspended solids is known, the resulting removal efficiency can be presented in terms of either settleable solids or total suspended solids. Additional research is needed to develop standardized protocols for the collection of solids and handling prior to analysis.

Alternative feeds are critical for the sustainable expansion of the marine finfish aquaculture industry. The industry uses wild-caught forage fish as a primary ingredient in farmed fish feeds. Alternative ingredients are needed to safeguard fisheries' sustainability and future aquaculture development. While there have been successes in alternative feeds, it is necessary to improve the existing options and identify alternative ingredients with higher concentrations of omega-3 polyunsaturated fatty acids (PUFAs). This study was designed to test a microalga, Schizochytrium sp., as a feed ingredient for sablefish (Anoplopoma fimbria) using six test diets. There were two fish-ingredient control diets: +FM+FO, which contained both fishmeal and fish oil, and -FM+FO, which contained fish oil, but no fishmeal. The remaining four diets contained alternative lipids and were completely fish-free. FF Flax contained flax oil as the only lipid source replacing fish oil. FF LowSc, FF ModSc, and FF HighSc contained a low, moderate, and high level of Schizochytrium sp. to replace fish oil, with flax oil content decreasing as the microalga increased. After a 20-week trial, sablefish growth differed across the feed treatments, with fish fed the high microalga-inclusion diet (FF HighSc) performing similarly to fish fed the fish-ingredient controls. Fulton's K condition factor, dry feed intake (DFI), and lipid productive value (LPV) were also influenced by treatment. For the four fish-free diets, specific growth rate increased with increasing inclusion of Schizochytrium sp. in the feed. Fillet fatty acid profiles were similarly influenced by diet treatment, generally reflecting the fatty acid profiles of the feed. Total fillet PUFAs were higher in sablefish from the fish-free treatments than the control treatments, with DHA increasing with increasing inclusion of dietary Schizochytrium. In contrast, EPA was higher in fillets from both fish-ingredient control treatments compared to fillets from the fish-free treatments, yet EPA remained higher than expected in sablefish fed the fish-free diets. Histologic evaluation of sablefish distal intestine and liver demonstrated that the microalga-inclusion diets were well tolerated and did not cause histomorphological changes in the tissues. These results suggest Schizochytrium sp. can increase PUFA concentrations in fish fillets without compromising fish health and growth, making it a viable ingredient for alternative sablefish feeds.

Sablefish (Anoplopoma fimbria) is a Pacific marine species that adapts well to aquaculture, grows extremely fast, and command a high market price. Because of environmental and regulatory concerns, increased production of this species is likely to occur in land-based systems. Little is known about the waste production characteristics of sablefish, information that will have a critical impact on the design of aeration, solid removal, and biofilter design for this species. It was found that the concentration of total suspended solids (TSS) in the effluent was extremely low and the mean TSS ranged from 0.9 to 1.7 mg/L. Compared to other important culture fish, sablefish produce significantly less fecal solids (5.2-7.9 % based on feed inputs) and less of their solids settled out (57.3-65.8 % of total suspended solids). TSS production following feeding of a special feed for reuse systems was significantly higher (51.9 %) compared to fish fed a conventional diet. The reduced production of TSS by sablefish is due to higher apparent digestibility coefficients and possible production of wastes that are not retained on the standard filter used for TSS analysis. Additional rinsing of the filters to remove salt and the use of large sampling volumes can significantly improve the accuracy of TSS analysis for marine culture species.

Sablefish, Anoplopoma fimbria (also called black cod), is a long-lived marine species with wide distribution extending from Baja California to Alaska, the Bering Sea, and through to the eastern coast of Japan. The landed weight of sablefish in the U.S. commercial fisheries is not large compared with other species; however, the exceptional value of sablefish has ranked it high compared with other species such as pollock, sockeye salmon, and Pacific cod. Sablefish are high in omega-3 fatty acids and have white firm flesh with superior quality and taste. Current population levels are lower relative to historic ones and harvests have decreased within the last decade. The exceptional value of sablefish and decreases in wild populations have stimulated the development of methods to commercially aquaculture this species. Over the last 20 years, significant progress has been made in addressing the production of sablefish, and while there is still research that needs to be completed, sablefish have been commercially aquacultured by a small number of Canadian companies. In the Pacific Northwest, it is relatively easy to collect sablefish broodstocks from the wild and to transition them to land-based rearing facilities. However, they must be maintained at cold temperatures to successfully reproduce. Captive broodstocks for genetic selection are not commercially available, though producers have begun their own development. Incubation conditions for yolk-sac larvae have been developed and currently require long incubation periods at low temperatures, elevated salinity, and light exclusion. Although incubation times are long, they do not require very much attention during this phase. Exogenously feeding larvae currently require a regimen of rotifers and Artemia prior to dry feed habituation. However, tank characteristics, water turbidity, temperature, and illumination, as well as live feed enrichments have been studied. With the research that has been accomplished so far, survival rates of 10-40% have been routinely obtained at the larval stage. Despite a scarcity of species-specific nutritional studies, researchers have shown that sablefish can be successfully cultured from the juvenile to the adult stage on commercial salmon feeds. Off-the-shelf salmon feeds have been used successfully in net-pen grow-out trials and are used by commercial producers. In addition, sablefish have proven to be a good cold-water marine model for alternative feeds research. Still, research is needed to optimize nutritional requirements for all life stages of sablefish, develop practical feeds with these nutrient profiles, optimize feeding schedules, and produce life-stage specific diets since the growth of sablefish differs according to size-most likely reflective of their complex life history. Sexually dimorphic growth in sablefish occurs during the typical grow-out period, affecting time to harvest, the proportion of undersized (male) fish, and thus overall economic return to the producer. Production of all-female monosex offspring at semi-commercial scale using F-1 progeny of neomales (XX males) generated through dietary treatment with 17 alpha-methyltestosterone is now possible. Results of long-term feeding trials suggest that time to harvest at 2.5 kg from stocking at 75 g may be reduced by almost 3 months when monosex stocks are used. Econometric models reveal that internal rates of return are 11-15% higher for monosex relative to mix-sex stocks over a 10-year period under typical cage culture conditions. Sablefish are susceptible to diseases (furunculosis and vibriosis) brought on by atypical Aeromonas salmonicida and Vibrio anguillarum. Vaccination of sablefish using commercial vaccines to A. salmonicida (typical and atypical) has demonstrated that fish can be protected against a subsequent challenge by A. salmonicida, but this has only been effective by injection of the vaccine (not immersion) and how long the protection lasts has not been studied. More research is required to develop more effective vaccines, methods for vaccine delivery, and to understand conditions (ontogenetic and environmental) that may promote or enhance pathogenesis.

As diets fed to juvenile steelhead (progeny of anadromous rainbow trout, Oncorhynchus mykiss) reared in conservation hatcheries contain relatively high levels of protein and lipid supplied primarily by fish meal and fish oil, a 12-week feeding trial was conducted to evaluate alternative ingredients for this species. Using a factorial design, Spirulina meal and a plant oil mixture were evaluated as partial or complete replacements of dietary fish meal and fish oil, respectively. Thus, two diets containing 0 or 50% substitution of Spirulina for fish meal were extruded and top-coated with fish oil or a 63:37 mixture of canola and flaxseed oils. Each of the four dietary treatments was fed to quadruplicate groups of 100 steelhead initially weighing 12.4 g/fish. Steelhead growth rate and feed efficiency were not significantly affected by partial replacement of dietary fish meal with Spirulina, but growth responses were significantly reduced by replacement of dietary fish oil with plant oil. Lipid and protein apparent digestibility coefficients (ADC) were significantly higher in steelhead fed the fish meal diets compared with fish fed the Spirulina diets and significantly higher in steelhead fed the plant oil diets compared with fish fed the fish oil diets. Whole body fatty acid profiles generally reflected those of the diets such that percentages of 18:2n-6 were significantly higher and n-3 polyunsaturated fatty acids (PUFA), including 20:5n-3 and 22:6n-3, were significantly lower in fish fed the Spirulina and plant oil diets compared with those fed the fish meal and fish oil diets. Plasma total cholesterol concentration was significantly reduced in fish fed the Spirulina diets and in fish fed the plant oils diets. Growth results suggest Spirulina is a suitable replacement for 50% of dietary fish meal for steelhead whereas a mixture of canola and flaxseed oil is not suitable as a complete replacement for fish oil in diets for this species.

Turkish Towel Chondracanthus exasperates and taurine were added to alternative plant-based feeds for juvenile sablefish Anoplopoma fimbria to evaluate the effect of these ingredients, alone or combined, on fish growth, feed intake and efficiency, whole body nutrient composition, and liver histomorphology. Fish growth was significantly increased with the addition of taurine, and to a lesser extent, Turkish Towel to the experimental feeds. Feed efficiency and protein retention were significantly improved with the addition of taurine, but were unaffected by Turkish Towel addition. As expected, whole body taurine content was significantly affected by taurine addition. Increases in whole body lipid were observed with both taurine and Turkish Towel addition, with a significant interaction between the two factors. Liver histomorphology was generally normal; however, histopathologic changes were observed in some fish at the end of the experiment. The occurrence of hepatocellular nuclear pleomorphism and clear cell foci was less among fish that had received the Turkish Towel feeds. The addition of taurine had no effect on the number of fish with a histopathologic change. Overall, results from this study reaffirm taurine supplementation is beneficial to sablefish receiving plant-based feeds and indicate Turkish Towel may be a promising feed ingredient for this species.

To quantify the efficacy and cost of different soya protein ingredients, heated soya beans (HSB) and underprocessed (SB) full-fat soya beans (FFSB), soya protein concentrate (SPC) and trim waste from Pacific whiting (Merluccius productus) were incorporated into feeds for the cold water marine sablefish (Anoplopoma fimbria). Feed ingredients for this study were processed using an experimental heated ball mill with demonstrated potential as an affordable process for rural or small-scale feed production. The three feed treatments were formulated with equal amounts of soya protein and Pacific whiting process trim. The three feed treatments contained 46% protein and 18% lipid as dry matter. Three 480-L tanks of 10 fish were used to evaluate each of the three feed treatments. Fish were fed to satiation every 2 days for 8 weeks. Weight gain of the treatment groups ranged between 56% and 105% over the course of the study. Fish growth was significantly better among fish receiving the feeds containing HSB and SPC than a feed containing SB. At the conclusion of the study, histomorphologic evaluations of the distal intestines of final fish were conducted. Varying levels of inflammation were measured for all three treatments. Fisher's exact test showed a significant reduction in mononuclear cell infiltration among fish fed heat-treated full-fat soya beans vs those receiving underprocessed full-fat soya beans. Fish receiving HSB feed had significantly lower intestinal inflammation than SB fish. Based on our results, cost savings of $ 0.253/kg were calculated for the HSB feed over the SPC feed.

Turkish towel (Chondracanthus exasperatus), Pacific dulse (Palmaria mollis, also known as Red ribbon seaweed), and sea lettuce (Ulva spp.) were cultivated in a land-based intensive culture system at the Manchester Research Station, USA from August 2013 to September 2014. Macroalgae were grown in tumble-aerated tanks, harvested bimonthly for seasonal growth calculations, and analyzed for protein, lipid, ash, and amino acid content. Growth rate of all three species exhibited a similar pattern, with the highest specific growth rates occurring during the summer months (Turkish towel: 7.8%, Pacific dulse: 8.2%, and sea lettuce: 6.2%). Growth of all three species was lowest around winter solstice; with negative growth only observed in sea lettuce. On a dry weight basis significant differences in protein content existed between the three species with highest values for sea lettuce (29.5 +/- 1.4%). Lipid content varied between species (0.95-2.78%) with significantly higher lipid observed in sea lettuce (0.58-4.82%). No significant differences were detected on a seasonal basis among each species. Essential amino acids accounted for 43 +/- 0.9 to 47 +/- 1.2% of total amino acids with Turkish towel having the highest value. Turkish towel had a significantly higher taurine level (0.82 +/- 0.27) than the other macroalgae. The levels of persistent organic pollutants and heavy metals were low. The estimated annual product of the three species ranged from 50-to 70-mt dry weight ha(-1) y(-1), significantly higher than conventional crops. Land-based culture of these species can produce year-round harvest, consistent product quality, and low contaminant levels.

Female coho salmon, Oncorhynchus kisutch, were fed one of two experimental feeds containing lipids with markedly different stable 13C isotope signatures during the late cortical alveolus, lipid droplet, and vitellogenesis stages of secondary oocyte growth. Ovarian and muscle lipids fatty acid concentrations were significantly affected by treatment during all three stages of development. Stable 13C isotope analyses confirmed that dietary lipids were incorporated into both ovarian and muscle lipids during all three stages and revealed that ovarian lipids were more affected than muscle lipids during vitellogenesis. Arachidonic acid (ARA) was incorporated into ovarian lipids at the highest rate of all fatty acids examined with the greatest uptake observed during the cortical alveolus and lipid droplet stages of development. Docosahexaenoic acid (DHA) was incorporated into ovarian lipids at the next highest rate with the greatest uptake observed during the lipid droplet stage of development. The presence of an ovary specific, fatty acid transfer mechanism is proposed. Results from this study demonstrate the ability to greatly alter the fatty acid composition of ovarian lipids through a dietary change during secondary oocyte growth and may be of great interest to producers of farmed salmon and salmon broodstock programs.

A 3-month feeding trial with tongue sole Cynoglossus semilaevis broodstock was conducted before and during the spawning season to investigate the effects of dietary arachidonic acid (ARA) on the production of sex steroid hormones and gonadal gene expression of key proteins in steroidogenesis. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation (C, 0.58% ARA of total fatty acids (TFA)) and two diets with low (5.14% of TFA, ARA-L) or high ARA (15.44% of TFA, ARA-H) supplementation. The diets were randomly assigned to 9 tanks of 3-year-old tongue sole (10 females and 15 males in each tank). Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. At the end of the feeding trial, tissue samples from mature females (MF, with spontaneous ovulation), immature females (IMF, early vitellogenesis), and mature males (MM, expressing milt) were collected to assay the production of sex steroid hormones, gonadal gene expression of sex steroid-synthesizing proteins, as well as the fatty acid profiles of gonad, liver and muscle lipids. Results showed that ARA supplementation significantly reduced the estradiol production in females, but stimulated the testosterone production in males. ARA supplementation significantly reduced the mRNA expression of aromatase in ovaries but significantly increased the gene expression of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in testes. In mature ovaries, diet ARA-L significantly reduced the gene expression of follicle stimulating hormone receptor (FSHR), 3 beta-EISD, and 17 beta-HSD; however, in immature ovaries, it significantly increased the gene expression of FSHR, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450ssc), 3 beta-HSD, and 17 beta-HSD. In all gonads, 17 alpha-hydroxylase (P450c17) responded to dietary ARA differently from other sex steroid-synthesizing proteins. ARA was preferentially accumulated in tongue sole gonad lipids. ARA concentrations were highest in gonad, liver and muscle lipids of MM fish and lowest in MF fish. Compared to female tongue sole, males had higher DHA concentrations in gonad lipids, but lower concentrations in liver lipids. In conclusion, results suggest dietary ARA regulates sex steroid hormone synthesis in tongue sole broodstock, and accumulates in gonad lipids, depending on both fish gender and maturation stage. Dietary ARA supplementation appears more important for male fish than for female fish, and more important for immature females than for mature females.Statement of relevance: This study is beneficial to the broodstock diet formulation. (C) 2016 Elsevier B.V. All rights reserved.

A feeding trial was conducted to investigate the use of alternative fish feeds produced from fish-trim waste in high plant protein diets for juvenile sable-fish (Anopoploma fimbria). Fish meal in the control diet (CD) was replaced in the experimental diets by low molecular weight hydrolysate (LMWH) protein derived from Pacific whiting (Merluccius productus) processing waste, or by Atlantic salmon (Salmo salar) processing trim (ST), which was incorporated into the feed with an experimental heated ball mill. The feeding trial was conducted in an indoor recirculating seawater system and each feed was randomly assigned to triplicate groups of 50 fish (average initial body weight of 57.5 g). The results showed that compared to the control diet, the diets containing LMWH or ST significantly increased feed consumption and fish weight gain. The ST group showed a significantly higher weight gain than the LMWH group. The ST feed, but not the LMWH feed, had a significantly lower feed conversion ratio than the CD feed. The ST feed increased lipid retention efficiency and lipid content in whole body tissue. These results demonstrate that salmon fish trim waste and enzyme hydrolyzed whiting trim in high plant protein diets can increase the performance in sablefish.

Sablefish (Anuplupumu fimbriu) is a highly desired seafood product, which encourages development of sustainable aquaculture methods for this marine fish. Conventional marine fish-based feeds provide essential nutrients including long chain tatty acids for piscivorous species such as sablefish. Alternative terrestrial ingredients could reduce fishing pressures on pelagic species that are the source of fish meal and fish oil, and improve source sustainability. Using juvenile sablefish, we compared the effects of a standard fish-based diet to two diets that contained primarily terrestrial plant ingredients with flaxseed or corn oil replacing the added fish oil. After an 8-week trial feeding period, there were striking differences attributable to diet. Fish receiving the alternative feeds had lower weight gain and shorter length than fish receiving the fish-based feed, suggesting sablefish obtained lower nutrients from the alternative feeds. Among the histological differences, the intestinal mucosa was significantly less vacuolated and the frequency of intestinal mucous cells was reduced in alternative feed fish. The most dramatic lesions were observed in the liver, where severe bile duct hyperplasia (53%, flaxseed oil diet; 33%, corn oil diet), and hepatocellular lesions (nuclear pleomorphism/megalocytosis, regeneration, hypertrophy, clear cell foci) occurred in only alternative feed fish. The hepatic and biliary lesions indicate the alternative diets may be deficient or possibly harmful to sablefish. The bacterial community structures from corn oil fish showed much less diversity than those for the other diets, and the microbiome structures from the three diets were distinctly different from each other. The intestinal microbiome for the fish-based diet included the largest number of families (68), and these fish also had the largest number of unique bacterial families (11) compared to those for corn oil (two) or flaxseed oil (one) fish. Regardless of diet, the stomach and intestinal microbiomes differed significantly from each other, and the feed microbiome differed from all gastrointestinal communities, suggesting that feed is not a significant source of gut bacterial diversity. Similar to other teleosts, the sablefish gastrointestinal microbiome is dominated by Bacteroidetes, Firmicutes, and Proteobacteiia. These results suggest that diet induced shifts in microbiome can occur relatively quickly in sablefish, but the shifts may not be sufficiently adaptive or cannot overcome nutrient deficiencies. This multidisciplinary study demonstrates the utility of histology and microbiology in characterizing dietary effects for novel aquaculture species.Statement of relevance: Physiological assessments such as gastrointestinal microbiomes and histopathology can provide a near-term evaluation of the nutritional adequacy of alternative feeds, such as plant-based lipid diets for marine carnivorous finfish. This is the first examination of the microbiome of sablefish, a marine species under development for sustainable aquaculture. Published by Elsevier B.V.

A feeding trial was conducted to investigate the use of alternative fish feeds produced from fish-trim waste in high plant protein diets for juvenile sablefish (Anopoploma fimbria). Fish meal in the control diet (CD) was replaced in the experimental diets by low molecular weight hydrolysate (LMWH) protein derived from Pacific whiting (Merluccius productus) processing waste, or by Atlantic salmon (Salmo salar) processing trim (ST), which was incorporated into the feed with an experimental heated ball mill. The feeding trial was conducted in an indoor recirculating seawater system and each feed was randomly assigned to triplicate groups of 50 fish (average initial body weight of 57.5 g). The results showed that compared to the control diet, the diets containing LMWH or ST significantly increased feed consumption and fish weight gain. The ST group showed a significantly higher weight gain than the LMWH group. The ST feed, but not the LMWH feed, had a significantly lower feed conversion ratio than the CD feed. The ST feed increased lipid retention efficiency and lipid content in whole body tissue. These results demonstrate that salmon fish trim waste and enzyme hydrolyzed whiting trim in high plant protein diets can increase the performance in sablefish. The IJA appears exclusively as a peer-reviewed on-line open-access journal at http://www.siamb.org.il. To read papers free of charge, please register online at registration form. Sale of IJA papers is strictly forbidden. Sale of IJA papers is strictly forbidden.

This study was conducted to investigate the effects of different taurine levels on the conjugated bile acid composition and growth of juvenile rockfish. Five taurine level diets were made by the supplementation of taurine (0%, 0.5%, 1.0%, 1.5% and 2.0%) to a basal diet. Fish meal washed with 70% ethanol to exclude taurine was used for the sole protein source. Feeding experiments were accomplished at 15°C using juvenile fish (initial BW: 13.5 g). Fish were fed the experimental diets for 4 months. At the end of experiments, fish were weighed and stored at −80°C for analysis of free amino acids and conjugated bile acids contents. The growth performance and feed efficiency of Korean rockfish were improved by taurine supplementation in the experimental diets. The taurine contents of the whole body increased with the increase in the taurine supplementation. The primary conjugated bile acids in gall bladder were taurocholic acid (83.5–165.6 mg mL−1) and taurochenodeoxycholic acid (6.3–20.0 mg mL−1). Total bile acids increased with increases in dietary taurine. Taurocholic acid content was more than 95% of the total conjugated bile acids. This indicates that taurine is the sole amino acid to make conjugated bile acid in Korean rockfish. Dietary taurine levels improved the conjugated bile acid composition in juvenile Korean rockfish.

Juvenile sablefish were fed a low taurine, basal feed with seven graded levels of supplemental taurine to determine taurine requirements for growth and feed efficiency. The basal feed was plant based, formulated primarily with soy and corn proteins with a minimal (9%) amount of fishmeal. The unsupplemented, basal feed contained 0.14% taurine. Experimental feeds were supplemented with 0, 0.25, 0.50, 1.0, 1.5, 3.0, and 6.0% taurine. Using the five parameter, saturated kinetic model (5 SKM), peak weight gain was predicted at 1.5% dietary taurine. Optimum weight gain, as defined as the region of the 5 SKM curve corresponding to at least 95% of peak, was predicted between 0.4% and 5.8% dietary taurine. Peak feed efficiency was predicted at 1.1% dietary taurine with optimum weight gain predicted between 0.4% and 4.2%. Whole body and muscle tissue protein and lipid content were not affected by taurine supplementation. Tissue taurine content increased asymptotically with increasing dietary taurine supplementation. Whole body tissue became saturated at 0.25±0.02% taurine, expressed on a wet weight basis. Muscle tissue became saturated at 0.34±0.02% taurine. Results from this study should increase the performance of alternative, plant based feeds formulated for sablefish and enable regulatory agencies better estimate the potential human exposure to taurine from the consumption of sablefish receiving these feeds.

Results of a past study on lean and siscowet lake trout (Salvelinus namaycush) reared under identical conditions from conception indicated that differences in growth and morphometry between these morphotypes have a genetic basis. Using these cultured lake trout, we found that siscowet lake trout had higher lipid levels and lower glycogen levels as compared with lean lake trout in skeletal muscle and liver. Lean lake trout also had higher circulating levels of lipids and glucose compared with siscowet lake trout. Analysis of F-1 progeny from crosses of the cultured morphotypes showed that progeny of crosses between siscowet females and siscowet males had higher lipid levels than all other crosses. The combined results indicate that the lake trout morphotypes differ substantially in the storage of energy, which may be related to their specific life histories. Siscowets store energy preferentially as lipid and appear to be more efficient in moving lipid from the blood into the muscle and liver. The lipid in siscowets may be adaptive for regulating buoyancy as well as an essential energy reserve for reproduction.

Copyright © 2014 The Korean Society of Phycology 227 http://e-algae.kr pISSN: 1226-2617 eISSN: 2093-0860 Nitrogen allocation of Gracilaria tikvahiae grown in urbanized estuaries of Long Island Sound and New York City, USA: a preliminary evaluation of ocean farmed Gracilaria for alternative fish feeds Ronald B. Johnson*, Jang K. Kim, Lisa C. Armbruster and Charles Yarish Resource Enhancement and Utilization Technologies Division, Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Blvd. E, Seattle, WA 98112, USA Department of Marine Sciences, University of Connecticut, One University Place, Stamford, CT 06901, USA Department of Ecology and Evolutionary Biology, University of Connecticut, One University Place, Stamford, CT 06901, USA

Coho salmon Oncorhynchus kisutch are semelparous spawners with highly synchronized oocyte growth. Plasma was collected from maturing female fish and plasma lipids were quantified by lipoprotein class. Stable C-13 isotopes were employed to investigate the origins of plasma lipids. Plasma lipoproteins were partitioned into the very low density (VLDL), low density (LDL), high density (HDL) and very high density (VHDL) lipoprotein classes. Lipids from all lipoprotein classes increased between the lipid droplet and early vitellogenesis stages of oocyte growth and VHDL lipids continued to increase through mid vitellogenesis (P < 0.05). During vitellogenesis, total plasma lipid concentrations were similar to the sum of lipoprotein lipids (P = 0.51). Plasma vitellogenin determined by an ELISA method was very well correlated with VHDL lipid during vitellogenesis (R-2 = 0.91, n = 15). In general, the delta C-13 values of plasma lipids reflected that of feed (exogenous) and muscle (endogenous) lipids when feed and muscle delta C-13 values were similar, and were intermediate when differences existed between the two lipid sources. With one exception, the delta C-13 values of lipids from all lipoprotein classes within a plasma sample were similar. Results indicate that during sexual maturity, lipids from all plasma lipoprotein classes originate from a common pool of exogenous and endogenous lipids.

Female coho salmon Oncorhynchus kisutch were fed one of two broodstock diets during vitellogenesis to evaluate the contribution of dietary lipids to egg lipids and to assess any embryo or fry quality differences that were attributable to treatment. The diets contained lipids with different fatty acid profiles and carbon stable isotope signatures (delta C-13). Diets were formulated by top-dressing a low-fat salmon broodstock feed with either sardine oil (fish oil feed) or an algal oil-corn oil blend (algal oil feed). The added oils were balanced for total n-3 fatty acid content but contained markedly different levels of linoleic acid (LA), eicosapentaenoic acid, and docosahexaenoic acid (DHA). Analysis of delta C-13 revealed that dietary lipids were significantly incorporated into egg lipids during vitellogenesis and that polar and neutral lipid fractions were equally affected. Eggs of fish in the algal oil treatment group had significantly higher levels of DHA and significantly lower protein content than the eggs of fish in the fish oil treatment group. Embryo survival and fry survival and growth were similar between the two treatment groups. Eggs from the algal oil treatment additionally had higher levels of LA, and there was evidence of direct elongation of LA to eicosadienoic acid (20:2[n-6]) and bioconversion of LA to arachidonic acid by the fish. Results from this experiment demonstrate the feasibility of increasing the DHA content of egg lipids in cultured salmonids without a concomitant decrease in egg or fry quality. The proposed enrichment would allow for the production of a value-added, high-DHA product for the cured roe market without reducing the value of eggs that are destined for the hatchery market.

In Lake Superior there are three principal forms of lake trout (Salvelinus namaycush): lean, siscowet and humper. Wild lean and siscowet differ in the shape and relative size of the head, size of the fins, location and size of the eyes, caudal peduncle shape and lipid content of the musculature. To investigate the basis for these phenotypic differences, lean and siscowet lake trout, derived from gametes of wild populations in Lake Superior, were reared communally under identical environmental conditions for 2.5 years. Fish were analysed for growth, morphometry and lipid content, and differences in liver transcriptomics were investigated using Roche 454 GS-FLX pyrosequencing. The results demonstrate that key phenotypic differences between wild lean and siscowet lake trout such as condition factor, morphometry and lipid levels, persist in these two forms when reared in the laboratory under identical environmental conditions. This strongly suggests that these differences are genetic and not a result of environmental plasticity. Transcriptomic analysis involving the comparison of hepatic gene frequencies (RNA-seq) and expression (quantitative reverse transcription-polymerase chain reaction (qPCR)) between the two lake trout forms, indicated two primary gene groups that were differentially expressed; those involving lipid synthesis, metabolism and transport (acyl-CoA desaturase, acyl-CoA binding protein, peroxisome proliferator-activated receptor gamma, and apolipoproteins), and those involved with immunity (complement component C3, proteasome, FK506 binding protein 5 and C1q proteins). The results demonstrate that RNA-seq can be used to identify differentially expressed genes; however, some discrepancies between RNA-seq analysis and qPCR indicate that methods for deep sequencing may need to be refined and/or different RNA-seq platforms utilized.