Christopher C. Kohler

Health and Condition in Fish: The Influence of Lipids on Membrane Competency and Immune Response

Traditionally fisheries biologists have used various metrics to indicate the condition and, by implication, health of fish. These indices are usually based on relationships between length and weight (Anderson and Neumann 1996). Although such metrics can, under some circumstances, provide a quick estimate of a fish’s condition, their ability to shed light on the underlying cause-and-effect relationship(s) governing a fish’s health and nutritional status are limited. Biochemical measures (e.g. lipids including fatty acids (FA) and sterols, proteins and their constituent amino acids, and trace elements) offer complimentary measures to assess, in a more specific way, the condition and underlying health of fish. Fatty acids and other lipids affect the health of fish in many ways; including, but not limited to, their effects on growth, reproduction, behavior, vision, osmoregularity, membrane fluidity (thermal adaptation), and immune response. In this review, we focus on the latter two roles that lipids play in mediating the health and condition of fish.

Mass-Marking Otoliths of Larval and Juvenile Walleyes by Immersion in Oxytetracycline, Calcein, or Calcein Blue

Abstract Immersion of larval and juvenile walleyes Stizostedion vitreum for 6 h in a 500-mg/L solution of oxytetracycline hydrochloride or Calcein resulted in fluorescent marks on 100% of the otoliths. Few marked fish (≤27.0%) were found after immersion in Calcein blue, Immersion of larvae at 15°C resulted in significantly higher mortality (57.7%) than at 10°C (20.9%). Mortality at 10°C was lowest for larvae immersed in oxytetracycline (9.0%) and greatest for those immersed in Calcein (41.6%). Juvenile mortality (1.3–32.7%) was correlated with high pond water temperatures during June (26.1°C) and August (32.2°C). All of the juveniles survived when immersed in any of the three chemicals in cases where pond water temperatures were less than 20°C at the time of collection.

Challenges and Opportunities in Finfish Nutrition

Abstract Much of the criticism leveled at aquaculture (e.g., dependency on animal-derived feedstuffs, nutrient-laden effluent discharges, and increased organic contamination in edible products) can be traced to the feeds in use. Accordingly, finfish nutritionists are being challenged to formulate feeds that not only meet the nutritional requirements of livestock but also minimize production costs, limit environmental impacts, and enhance product quality. These challenges not only add considerable complexity to finfish nutrition but also afford opportunities to avoid some of the mistakes made by other industries in the past. From a review of the current status of finfish nutrition with respect to major nutrient classes, we comment on future opportunities and promising avenues of research. Alternative protein sources, specifically those derived from marine bycatch, plants, and microbes, are discussed, as well as methods to facilitate their implementation in finfish feeds. Dietary lipid, its role in fish bio...

Modification of Fillet Composition and Evidence of Differential Fatty Acid Turnover in Sunshine Bass Morone chrysops × M. saxatilis Following Change in Dietary Lipid Source

Marine oil-based finishing diets have been used to restore fillet FA profile in several “medium-fat” fleshed aquaculture species, and a simple dilution model describing FA turnover has been established to predict and tailor final fillet composition. We evaluated finishing diet efficacy and suitability of the dilution model to describe patterns of FA change in a lean-fleshed model, sunshine bass. Two practical diet (45% crude protein, 15% crude lipid) were formulated, respectively containing corn oil (CO) or menhaden oil (MO) as the primary lipid sources. Sunshine bass (age 1 [⊃ 14 mo], 347 ±8.6 g, mean individual weight ±SEM) were stocked in a recirculating system and fed the diets according to different feeding regimens during the final 28 wk of the production cycle. Control groups were fed the CO or the MO feeds exclusively; whereas, the remaining treatment groups were transitioned from the CO diet to the MO diet at 4−, 8−, or 12-wk intervals. Upon completion of the feeding trial, fish were harvested, and production performance and fillet composition were assessed. Replacing MO with CO as the primary lipid source in sunshine bass diets yielded fillets with distinctly different FA profiles; however, finishing with a MO-based diet offered significant compensation for CO-associated reductions in fillet long-chain highly unsaturated FA (LC-HUFA). Although complete restoration was not observed, we achieved significant augmentation of endogenous n−3 FA within 4 wk of feeding the MO diet, and observed a significant increase in LC-HUFA and a beneficial shift in n−3∶n−6 FA ratio after 8 weeks. Simple dilution accurately predicted tissue composition for most FA; however, deviations from the model were noted, suggesting selective retention of n−3, PUFA, and LC-HUFA and preferential catabolism of saturates. We conclude marine oil-based finishing diets can rapidly augment beneficial FA levels in sunshine bass fillets; however, simple dilution models do not fully describe selective FA metabolism observed for this lean-fleshed fish.

Vitamin E requirements of the blue tilapia, Oreochromis aureus (Steindachner), in relation to dietary lipid level

Abstract The vitamin E requirement of the blue tilapia, Oreochromis aureus (Steindachner), was evaluated in semipurified diets containing two lipid levels (3% and 6% corn oil) and five levels (0, 10, 20, 40, and 80 mg/kg) of dl-α-tocopheryl acetate. Vitamin E-deficient fish exhibited significantly lower weight gains and feed conversion efficiencies compared to the other fish. In addition, the following vitamin E deficiency signs were observed; skin and fin hemorrhages, anorexia, impaired erythropoiesis, muscle degeneration, ceroid depositions in liver and spleen, and lack of skin color. The vitamin E requirement of the blue tilapia was estimated at 10 mg dl-α-tocopheryl acetate/kg of diet at 3% dietary lipid and at 25 mg/kg of diet at 6% dietary lipid when diets contained 120 mg/kg BHA. It is recommended that vitamin E requirements be expressed as a function of dietary lipid level; 3–4 mg α-tocopheryl acetate per percent corn oil per kg of diet for the blue tilapia.

Influence of Dietary Replacement of Menhaden Oil with Canola Oil on Fatty Acid Composition of Sunshine Bass

Abstract The replacement of menhaden Brevoortia spp. oil with graded levels of canola oil in diets fed for 20 weeks to sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) significantly impacted the fatty acid composition of fillets and livers. As the amount of canola oil increased from 0% to 100% of the oil in the diet, the amount of 18:1(n-9) and 18: 2(n-6) fatty acids in fillets increased linearly, whereas the amounts of 20:5(n-3), 22:6(n-3), long-chain n-3 highly unsaturated fatty acids (HUFAs), and total long-chain HUFAs in the fillets decreased linearly. Total long-chain n-3 HUFA levels did not differ significantly between fillets from fish fed a diet with 50% canola oil and those from fish fed 100% menhaden oil. The experimental diets also significantly altered the fatty acid compositions of the livers, though fatty acid levels were highly variable within and among treatments and differences usually were not as pronounced as differences in fillets. We observed no signi...

Habituation to Captivity and Controlled Spawning of White Bass

Abstract We successfully spawned white bass Morone chrysops that had been habituated to captivity in indoor tanks for over 1 year and whose cycles were entrained by simulated temperature and light regimes. In summer (1990) 300 white bass (300–600 g) of an approximately even sex ratio were distributed into three 10,000-L water-recycle systems. One system was maintained under an ambient photoperiod and temperature regime, one was maintained under a regime that simulated a 9-month (compressed) annual cycle of changing photoperiod and temperature, and one was held at a temperature range at or above spawning temperature (15–25°C) and constant photoperiod (14 h light: 10 h darkness). By human chorionic gonadotropin (hCG) injections (1,100 IU/kg for female fish; 275 IU/kg for males), we induced the compressed-cycle fish to spawn in March 1991 and the ambient-cycle and constant-cycle fish to spawn in May 1991. Constant-cycle fish injected with hCG in March 1991 failed to spawn. Male white bass continuously held a...

Fatty Acid Profile of Sunshine Bass: II. Profile Change Differs Among Fillet Lipid Classes

Fatty acid (FA) profile of fish tissue mirrors dietary FA profile and changes in a time-dependent manner following a change in dietary FA composition. To determine whether FA profile change varies among lipid classes, we evaluated the FA composition of fillet cholesteryl esters (CE), phospholipids (PL), and triacylglycerols (TAG) of sunshine bass (SB, Morone chrysops × M. saxatilis) raised on feeds containing fish oil or 50:50 blend of fish oil and coconut, grapeseed, linseed, or poultry oil, with or without implementation of a finishing period (100% FO feed) prior to harvest. Each lipid class was associated with a generalized FA signature, irrespective of nutritional history: fillet PL was comprised largely of saturated FA (SFA), long-chain polyunsaturated FA (LC-PUFA), and total n-3 FA; fillet TAG was higher in MC-PUFA and total n-6 FA; and fillet CE was highest in monounsaturated FA (MUFA). Neutral lipids reflected dietary composition in a near-direct fashion; conversely, PL showed evidence of selectivity for MC- and LC-PUFA. Shorter-chain SFA were not strongly reflected within any lipid fraction, even when dietary availability was high, suggesting catabolism of these FA. FA metabolism in SB is apparently characterized by a division between saturated and unsaturated FA, whereby LC-PUFA are preferentially incorporated into tissues and SFA are preferentially oxidized for energy production. We demonstrated provision of SFA in grow-out feeds for SB, instead MC-PUFA which compete for tissue deposition, meets energy demands and allows for maximum inclusion of LC-PUFA within fillet lipids.

Cold Tolerance and Fatty Acid Composition of Striped Bass, White Bass, and Their Hybrids

Abstract Cold tolerance of striped bass Morone saxatilis, white bass M. chrysops, palmetto bass (female striped bass × male white bass), and sunshine bass (female white bass × male striped bass) were compared under controlled laboratory conditions. Two groups of each taxon were acclimated at 20°C in a recirculating-water system housed in an environmental chamber and were fed either a natural or prepared diet for 84 d. The fatty acid composition of the natural diet was 13% more unsaturated than that of the prepared diet. Fish fed the natural diet subsequently had unsaturated: Saturated fatty acid ratios 10-25% higher than fish fed the prepared diet. After being subjected to identical simulated cold fronts (10°C drop in surface water temperature, as if the fish were confined in cages or pens), all groups of fish fed the prepared diet suffered high mortality (50-90%) whereas there was zero mortality among the groups receiving the natural diet. White bass and sunshine bass fed the prepared diet had higher sur...

Influence of Grow-Out Feed Fatty Acid Composition on Finishing Success in Nile Tilapia

Abstract The fatty acid (FA) composition of cultured finfish can be tailored by transitioning fish reared on alternative lipid-based, low long-chain polyunsaturated FA (LC-PUFA) content grow-out feeds to high LC-PUFA finishing feeds based on fish oil (FO) before harvest. To determine whether the FA composition of the grow-out feed influences finishing success in Nile tilapia Oreochromis niloticus, coconut (CO), grapeseed (GO), linseed (LO), and poultry (PO) oils were evaluated in grow-out feeds with respect to production performance and responsiveness to finishing. The production performance of Nile tilapia was unaffected by application of the various feeding regimes, indicating that this species can effectively utilize CO, GO, LO, PO, and FO in aquafeeds. Implementation of the alternative lipid sources was associated with altered fillet FA composition. Although the differences were not significant in all cases, the levels of FO-associated FAs (e.g., 20:5[n-3] and 22:6[n-3]) were elevated among finished g...