Nutritional enrichment for rotifer is necessary for the stable production in larviculture. Although manufacturers recommend feeding amount for enrichment diets, the effects of these recommended amounts on nutritional enrichment of rotifer are unknown. We assessed the effects of normal and overdose amount of enrichment diets on nutritional enrichment of rotifer using batch and continuous culture methods. Rotifer populations in two culture systems were enriched using four enrichment conditions, matched two diet levels, and two enrichment durations: 0.25 g/L for 8 h (normal enrichment) 0.25 g/L for 24 h (longer enrichment), 0.75 g/L for 8 h (overdose enrichment), and 0.75 g/L for 24 h (overdose + longer enrichment). When the batch-cultured rotifer populations were enriched, longer and overdose enrichments could not make the fatty acid contents differ from the normal one. Overdose enrichment was most effective of all enrichment conditions when continuouscultured rotifer populations were used. In both culture methods, the docosahexaenoic acid (DHA) content under overdose + longer enrichment conditions was two to three times as high as normal enrichment conditions and it resulted in two-to threefold increase in DHA/eicosapentaenoic acid ratio by overdose + longer enrichment. Accordingly, it is possible to alter the fatty acid composition of rotifer by changing the enrichment method.
This work aimed to evaluate the relationship between morphological development, oxygen consumption and reduced mortality in larval ¢sh.We measured the resting metabolic rate (RM), speci¢c metabolic rate (SMR) and the change in the total length during the larval stage of four ¢sh species. Resting metabolism decreased from hatching to mouth opening, and then increased after mouth opening. The changes in the SMR were variable during the larval stage. After hatching, there was no increase in SMR in yolk-sac larvae. However, SMR increased between mouth opening and the onset of notochord £exion and then decreased during notochord £exion before ¢nally stabilizing. We observed two peaks in mortality during the larval period of all species: between mouth opening to the onset of notochord £exion and from the completion of notochord £exion to the juvenile stage based on the per cent mortality and the number of dead ¢sh collected from the bottom of the rearing tank. Interestingly, the changes in SMR coincided with these periods of mortality. We hypothesize that larvae require more energy during these periods of larval development and are thus more susceptible to mortality when energy is insu⁄cient. Thus, it is important to supply enough nutrition to larvae in during early development to prevent mass larval mortality.
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