Study Of Feeding Protocols For Orange-Spotted Grouper (Epinphelus Coioides) Larvae And Juvenile In Diet Transition

The use of live food organisms is currently considered as obligatory in the culture ofthe early life stages of most marine larvae and constitutes a significant portion of total fryculturing costs. Thus, two experiments were designed to investigate the feeding protocols,which substitution of live food by inert diet, for orange-spotted grouper larvae and juvenilein diet transition by natural stable isotopes aimed at reducing live feed inputs.The first examined start weaning at36days after hatch（DAH）. Orange-spottedgrouper （Epinphelus coioides） larvae were supplied with frozen Artemia adult which raisedon shrimp flakes for10days and FuXing inert diet as single diets and in three co-feedingregimes in which25,50and75%of frozen Artemia adult was replaced by FuXing inert dieton a dry weight basis. All treatments were reared until63dph and run in triplicate. Theresults indicate that the50%ID,75%ID and ID treatments did not differ significantly inspecific growth rate. LP treatment had significantly lower growth than any of thetreatments receiving inert diet, but the survival was highest in all treatments examined at51.00%.75%ID and ID treatments had significantly lower survival than the othertreatments at37.67%and38.67%,respectively. Carcass protein content of LP hadsignificantly higher than any other treatments.75%ID was significantly lower than othertreatments but no difference with50%ID in carcass protein content. Carcass lipid contentwere not significantly different among dietary treatments. At the beginning of theexperiment, the digestive tract in36dph larvae contains enough enzymes. Such as amylase,pepsin and lipase specific activities were0.242,411.90and30.25U/mg, respectively. Theamylase specific activities increased for all feeding regimes as time went on. At the endthe amylase specific activities from different dietary treatments were0.273⁰.462U/mg,significantly different. The magnitude increased with increasing quantities of inert diet.This increase was maybe the result of an extensive synthesis induced by the dietarycarbohydrate.Pepsin specific activities declined for all treatments with time. At the end the Pepsin specific activities from different dietary treatments were16.64²5.48U/mg. The crudeprotein content of frozen Artemia adult was significantly higher than FuXing inert diet, butLP was significantly lower than other treatments in pepsin specific activities, it may be noteffected by dietary protein level. The decrease in pepsin activity among dietary treatmentsmay be genetically programmed. It may be associated with morphological changes duringtransition period from larvae to juvenile.Lipase specific activities first declined and then a little slight increscent among dietarytreatments as time went on. At the end, the lipase specific activities for different feedingregimes declined with increasing proportion of inert diet. LP and25%ID were significantlyhigher than other treatments,449.32and443.38U/mg, respectively. It may be the result oflowω-3highly polyunsaturated fatty acid, especially eicosapentaenoic（EPA） anddocosahexaenoic （DHA） acid in frozen Artemia adult, which are essential fatty acid for theearly life stages of most marine larvae. Larvae and juvenile increased metabolic cycling ofnonessential nutrients to cope up with this nutrient deficit.The second experiment examined weaning at36days after hatch（DAH） too.Orange-spotted grouper （Epinphelus coioides） larvae were supplied with live Artemia adultwhich raised on shrimp flakes for ten days and RiQing inert diet as single diets and in threeco-feeding regimes in which25,50and75%of live Artemia adult was replaced by RiQinginert diet on a dry weight basis. The duration of the changeover period from live toartificial food is10days, after that all dietary treatments were supplied with only RiQinginert diet for14days. The results indicate that LP treatment had significantly lower growththan any of the treatments receiving inert diet,75%ID treatments was lower than any othertreatments in survival at58.33%.No significant differences were observed in carcassprotein content among dietary treatments, but ID treatment was significantly lower thanany other dietary treatments in carcass lipid content.The relative contributions from co-fed frozen Artemia adult and FuXing inert diet forgrowth of orange-spotted grouper （Epinphelus coioides） larvae and juvenile was assessedby analyzing the nitrogen stable isotope ratios (δ¹⁵N) in both diets and fish muscle. FrozenArtemia adult and FuXing inert diet showed significantly different δ¹⁵N values but similarnitrogen contents, so that all feeding regimes provided similar amounts of dietarynitrogen.The results indicate that fish muscle δ¹⁵N values were significantly influenced by thedifferent feeding regimes and LP,25%ID,50%ID,75%ID and ID treatments reachedisotopic equilibrium with their respective diets were21d,18d,18d,12d and9d,respectively; their final isotopic asymptotic values were12.29‰,13.65‰,14.78‰,16.07‰ and16.46‰, respectively. Nitrogen turnover rates in fish muscle from the different feedingregimes were0.080⁰.759d-1. A two-source, one-isotope mixing model was applied toestimate the nutritional contribution of frozen Artemia adult and FuXing inert diet to fishmuscle growth in the co-feeding regimes. Results suggest that observed nutrientcontributions from FuXing inert diet were significantly higher than expected contributionsindicated by proportions established in the co-feeding regimes. The relative contribution ofFuXing inert diet to fish muscle growth in larvae and juvenile was respectively,31.42%⁴0.25%for the25%ID regime;61.00⁶2.74%for the50%ID regime and83.40⁹2.94%for the75%ID regime. The contrasting levels of nitrogen isotopediscrimination between diet and fish muscle in larvae and juvenile reared on either frozenArtemia adult or FuXing inert diet was3.62‰and1.69‰,respectively; and indicaterelatively high utilization of nutrients from the inert diet.The results of the two experiments showed that it could be complete replacement oflive foods which metamorphosed orange-spotted grouper larvae depended on with RiQinginert diet. RiQing inert diet could be well ingested, digested and assimilated by larvae andjuvenile.