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 diets (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 [approximately 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.
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 significant differences in weight gain, feed conversion, or total lipid content among fish fed the different diets. Our results suggest that high levels of canola oil in growing diets of sunshine bass could be used for the majority of the production cycle, to be followed by a “finishing” diet that would elevate HUFA levels, thereby increasing the fillets' nutritional benefit to the human consumer.
Zooplankton utilization and their importance to channel catfish Ictalurus punctatus fry during pond culture is not well documented. Current fry stocking decisions are based on total zooplankton densities. We studied the feeding habits (zooplankton size and taxa selection) of channel catfish fry. Catfish fry just completing swim‐up were placed into glass aquaria or into cages in ponds and allowed to forage on natural zooplankton assemblages. The zooplankton sizes and taxa consumed by the fry were compared with the available sizes and taxa in the aquarium or pond environments. Rotifers and copepod nauplii were abundant in all environments but were never observed in the fry stomachs. Ostracods, adult copepods, and cladocerans were the only three taxa consumed. The data from both experiments indicated that ostracods were consumed in proportions equal to natural abundances, but in the field experiment larger ostracods were selected. Consumption of adult copepods and cladocerans depended on the relative proportions and sizes of each taxon present. Cladocerans, when available, appeared to be the preferred prey. When cladocerans were scarce, more copepods were eaten. We conclude that fry stocking decisions should focus on copepod, cladoceran, and ostracod densities and sizes rather than total zooplankton densities. Furthermore, the lengths of available zooplankton should be 450–700 μm for cladocerans, more than 650 μm for copepods, and more than 450 μm for ostracods.
We evaluated the dietary effects of graded levels of highly unsaturated fatty acids (HUFAs) fed to broodstock female white bass Morone chrysops on reproductive performance, egg hatchability, and larval survival of sunshine bass (female white bass × male striped bass M. saxatilis) through the endogenous feeding stage. Dietary treatments consisted of four isocaloric, isonitrogenous diets formulated to contain 45% crude protein and 15% lipid with graded levels of menhaden oil (0, 25, 75, and 100%) or corn oil as the dietary lipid variable. Significant differences existed among the dietary groups in egg fatty acids, which reflected levels in the maternal diet, especially for the neutral lipid component. Similar trends were also found in fatty acids of the polar lipid component and conservation of HUFAs; significantly higher quantities of linoleic acid (18:2[n‐6]) were associated with increasing dietary inclusion of corn oil. Eggs with higher hatchability were associated with higher levels of n‐3 HUFAs, including eicosapentaenoic acid (20:5[n‐3]), docosapentaenoic acid (22:5[n‐3]), and docosahexaenoic acid (22:6[n‐3]). Our results suggest that white bass broodstock females possess low and moderate regulatory control of fatty acid deposition to the egg within the neutral and polar components, respectively. These results indicate that little to no elongation or desaturation of dietary fatty acids occurs during egg development. Accordingly, the inclusion of elevated levels of dietary HUFAs for white bass broodstock appears to be warranted.
We report on the development of nine polymorphic microsatellite loci in nurse shark (Ginglymostoma cirratum) using a combination of enriched and unenriched subgenomic libraries. Based on the small percentage of positive clones in the unenriched library (0.4%) it appears that microsatellites are very scarce in nurse shark genomes. Numbers of alleles at polymorphic loci ranged from two to 15; observed heterozygosity ranged from 0.17 to 0.90. We expect these loci to be useful for studies of breeding structure and paternity.
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