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Trushenski J.,Southern Illinois University Carbondale | Woitel F.,Southern Illinois University Carbondale | Schwarz M.,Virginia Polytechnic Institute and State University | Yamamoto F.,International Initiative for Sustainable and Biosecure Aquafarming
North American Journal of Aquaculture | Year: 2013

The high cost and limited availability of fish oil makes plant-derived lipids attractive for aquafeed manufacturing, but replacing fish oil with these lipids can result in long-chain polyunsaturated fatty acid (LC-PUFA) deficiencies. Fatty acid metabolism, specifically the efficiency of LC-PUFA utilization, may be influenced by the dietary saturated fatty acid (SFA) content versus that of C18 polyunsaturated fatty acids (PUFAs). We assessed the growth and tissue composition of Cobia Rachycentron canadum (55.3 ± 0.2 g initial weight [mean ± SE]; 10 fish/tank, 3 tanks/diet) fed diets (~49% protein, ~10% lipid) containing fish oil; 22:6(n-3)-amended standard, partially hydrogenated, or fully hydrogenated soybean oil; and these same soybean oils supplemented with soybean lecithin for 8 weeks. Although survival (range = 97-100%), final weight (160-189 g), and feed conversion ratio (1.40-1.52) were unaffected by diet, differences were observed in weight gain (185-241%), specific growth rate (1.87-2.19% body weight/d), and feed intake (2.94-3.44% body weight/d). Significant effects of soybean oil type on final weight, weight gain, feed conversion ratio, specific growth rate, and feed intake were noted, with standard soybean oil generally outperforming the other soybean lipids when oil types were pooled across phospholipid supplementation treatments, whereas phospholipid supplementation had no significant effect on any of the performance measures. Differences in dietary fatty acid profile yielded differences in tissue composition. Feeding standard soybean oil resulted in the most greatly modified profiles, whereas the profiles of fish fed fully hydrogenated, completely saturated soybean oil were most similar to those of the fish oil-fed fish. The magnitude of profile change was greatest in the liver and fillet tissues and smallest in the eye and brain tissues. Although further research is necessary to demonstrate whether SFA-rich lipids can effectively reduce the LC-PUFA requirements of Cobia, it is clear that SFA-rich oils offer a strategic advantage in minimizing the effects of fish oil replacement on tissue fatty acid profile. © American Fisheries Society 2013. Source


Trushenski J.,Southern Illinois University Carbondale | Schwarz M.,Virginia Polytechnic Institute and State University | Takeuchi R.,International Initiative for Sustainable and Biosecure Aquafarming | Delbos B.,Virginia Polytechnic Institute and State University | Sampaio L.A.,Grande Rio University
Aquaculture | Year: 2010

Prevention is the most viable disease management strategy in aquaculture, and prevention is primarily driven by strategies to avoid or minimize the effects of stress. Unfortunately, there is little information available regarding the stress physiology of emerging aquaculture species or appropriate experimental stressing protocols for these fishes, and thus very little context in which to evaluate mitigation strategies. Accordingly, the stress response of cobia was evaluated following exposure to 2 experimental stressors: low water and air exposure. Juveniles were exposed to air for 1. min (AIR EXPOSURE), held for 15. min in water lowered to the fish's lateral midline (LOW WATER), or unchallenged (CONTROL) prior to the collection of blood samples at 0 (pre-challenge), 0.5, 1, 2, 6, 12, 24, 48, and 72. h post-challenge. Both stressors elicited classical haematological changes indicative of the generalized stress response, however, the magnitude of the response was consistently greater in the AIR EXPOSURE group. Plasma cortisol, glucose, and lactate concentrations increased rapidly in the AIR EXPOSURE and LOW WATER groups, peaking within 1. h of challenge. Cortisol returned to basal levels rapidly, whereas glucose and lactate remained elevated for a longer period of time. Regardless of the stressor used, fish recovered within 12. h of the challenge. The primary and secondary responses of juvenile cobia challenged with low water and air exposure appear to respond in a similar fashion to other species exposed to these experimental stressors. Both low water and air exposure are suitable experimental stressors for use in cobia based on their ability to induce a classical stress response and ease of implementation. © 2010. Source


Trushenski J.,Southern Illinois University Carbondale | Schwarz M.,Virginia Polytechnic Institute and State University | Lewis H.,Southern Illinois University Carbondale | Laporte J.,Southern Illinois University Carbondale | And 3 more authors.
Aquaculture Nutrition | Year: 2011

As a marine carnivore exhibiting exceptionally high growth rates, cobia are considered a species for which fish oil (FO) replacement may be difficult. However, partial, if not complete, FO replacement is necessary to ensure sustainability. We evaluated the effects of graded substitution of dietary FO with soybean oil (SO) in cobia culture. Feeds contained FO (100% FO), SO (0% FO) or blends of the two (67% FO, 33% FO) as the supplemental lipid source. Production performance was largely unaffected by partial replacement of FO with SO: feed intake and final weight were reduced only in the 0% FO dietary treatment. Fillet total lipid fatty acid (FA) composition differed among the dietary treatments, closely approximating dietary FA profile. As increasing amounts of FO were replaced, SO-associated FA became enriched within the fillet lipid at the expense of FO-associated FA. Fillet lipid classes were associated with a particular FA signature, regardless of dietary FA profile. SO can replace a substantial amount of dietary FO; however, juvenile cobia appear to exhibit a nominal requirement for intact long-chain polyunsaturated FA. Therefore, aggressive FO replacement may result in essential fatty acid deficiencies unless the feeds can be amended with alternative sources of these essential nutrients. © 2010 Blackwell Publishing Ltd. Source


Rodrigues R.V.,Grande Rio University | Schwarz M.H.,Virginia Polytechnic Institute and State University | Delbos B.C.,Virginia Polytechnic Institute and State University | Carvalho E.L.,International Initiative for Sustainable and Biosecure Aquafarming | And 2 more authors.
Aquaculture | Year: 2011

Cobia Rachycentron canadum is a fast growing fish with world-wide potential for aquaculture, and has been considered for rearing in recirculating aquaculture systems (RAS). Nitrate is considered the least toxic nitrogenous product in the ammonia nitrification process, but as it may accumulate in RAS, toxic levels can be reached. The objective of this study was to evaluate the acute toxicity and the histopathological effects of nitrate on juvenile cobia. Juveniles (6.87±0.36g; 11.8±0.19cm) were acutely exposed to six concentrations of nitrate (500-3000ppm NO 3 --N) plus a control during 96h. At the end of this period of exposure, juvenile cobia were sampled for histopathological evaluation. The estimated LC 50 of nitrate to juvenile cobia was equal to 2407 and 1829mg/L NO 3 --N at 24 and 96h, respectively. Cobia exposed to sub-lethal nitrate concentrations showed histopathologic alterations in the gills, esophagus and brain. The gills revealed epithelial hyperplasia with complete lamellar fusion, telangiectasia, and lamellar shorting induced by necrosis, and the esophagus presented hyperplasia of epithelium and mucus cells. In the brain, glial cells proliferation, satellitosis (microglial cells surrounding neurons with swollen and prenecrotic neurons), and Virchow-Robin spaces (enlarged perivascular spaces, EPVS) were observed. The results of the present study indicate that juvenile cobia have a high tolerance to acute exposure of nitrate. However, assorted histopathological responses were observed for cobia at sub-lethal nitrate concentrations. Therefore, further studies are needed to estimate safe chronic nitrate levels for juvenile cobia culture. © 2011 Elsevier B.V. Source


Trushenski J.,Southern Illinois University Carbondale | Schwarz M.,Virginia Polytechnic Institute and State University | Bergman A.,Southern Illinois University Carbondale | Rombenso A.,International Initiative for Sustainable and Biosecure Aquafarming | Delbos B.,Virginia Polytechnic Institute and State University
Aquaculture | Year: 2012

Cobia may require both eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids to meet dietary n -3 long-chain polyunsaturated fatty acid (LC-PUFA) demand. Growth performance is reduced when LC-PUFA-rich fish oil is replaced with soybean oil, a LC-PUFA deficient lipid, in cobia diets, but individual requirements for EPA and DHA have not been quantitatively determined. We assessed the growth performance and tissue fatty acid composition of juvenile cobia fed a fish oil-based positive control diet (FISH), a soy oil-based negative control diet (SOY), or experimental diets based on soy oil supplemented with EPA, DHA, or both at 50% or 100% of the concentrations typically observed in fish oil: (SOY. +. 50% EPA, SOY. +. 100% EPA, SOY. +. 50% DHA, SOY. +. 100% DHA, SOY. +. 50% BOTH, SOY +. 100% BOTH). Growth performance of fish fed the SOY was impaired relative to those fed the FISH diet. Supplementing the soybean oil-based diet with DHA, alone or in combination with EPA, restored performance. EPA supplementation had no effect on growth performance. Fatty acid composition of cobia fillet, liver, brain, and eye tissues was significantly affected by diet, but tissue profile change among fish fed any of the soy oil-based diets was less overt in the brain compared to the periphery. Diets supplemented with DHA and/or EPA resulted in increased tissue levels of these fatty acids, however, the maximal levels were observed in the FISH treatment. Our data suggest the dietary n -3 LC-PUFA requirement of juvenile cobia can be largely satisfied by DHA, and that EPA, if required, is required only in trace amounts. Soybean oil supplemented with DHA is an effective alternative to fish oil in juvenile cobia diets. © 2011 Elsevier B.V. Source

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