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This study examined the effects of feeding fermented tuna by-product (FTBP) on the growth, non-specific immune response, liver and intestinal morphology, and disease resistance of olive flounder Paralichthys olivaceus. Olive flounders (n = 20; 2 g) were randomly assigned into four dietary groups in triplicates. Fish were fed four test diets (50% crude protein; 10% crude lipid) for 10 weeks in which unprocessed tuna by-product (TBP) meal was replaced (on a protein basis) with 0% (FTBP0 as the control diet), 15% (FTBP15), 30% (FTBP30), and 60% (FTBP60) of FTBP protein. Results showed that growth performance, blood parameters, and proximate composition were not influenced by FTBP inclusion. Non-specific immune parameters such as superoxide dismutase activity in the FTBP30 and FTBP60 groups were significantly higher than in the FTBP15 and the control groups, whereas lysozyme and myeloperoxidase activities were not different. Liver histopathology revealed normal architecture in groups fed FTBP0 and FTBP15 diets although mild alterations were noted in the FTBP30- and FTBP60-fed groups. Intestinal villi height and muscular thickness were not significantly altered with FTBP inclusion. Moreover, higher cumulative survival rate was observed in the FTBP60-fed group than fish fed with the other diets following the 13-day challenge with E. tarda. Together, these results demonstrate that fermented tuna by-product meal could be included at 60% in olive flounder diets.

The stable vitamin C derivative, L-ascorbyl-2-monophosphate-Mg (AMP), was used as a supplement in practical diets for Asian sea bass, Lates calcarifer. Optimum growth, liver ascorbic acid (AA) saturation, and wound healing were determined. Sea bass (78.9±0.4 g) were fed a maintenance diet without vitamin C supplement for 25 days, then distributed into fifteen 1500-l oval fiberglass tanks at 30 fish each and fed one of five practical diets containing 0, 50, 100, 200, or 400 AMP mg/kg diet for 14 weeks. Fish fed the AMP-free diet exhibited clinical signs of vitamin C deficiency and significantly poorer final average weight, specific growth rate, protein efficiency ratio, feed conversion ratio, and hematocrit level (p<0.05). The level of AA in the sea bass brain increased as the level of dietary AMP increased. The AA concentration in the liver was similar at all AMP dietary levels. Body calcium of sea bass fed the AMP-free or 50 mg diets was significantly lower (p<0.05) than in fish fed the other diets. AMP enhanced wound healing regardless of supplement level, but fish fed the highest dietary AMP (400 mg/kg diet) exhibited histopathological changes in the liver. The dietary level of 50 mg AMP/kg diet was adequate for optimum growth, liver AA saturation, and prevention of clinical signs of vitamin C deficiency in 80-220 g sea bass. However, 100 mg AMP per kg diet was necessary for optimum body calcium.

Growth and feed efficiency were determined in red snapper, Lutjanus argentimaculatus (Forsskal 1775), fed diets containing L-ascorbyl-2-monophosphate-Mg (AMP). Fish (13.39±0.08 g) were fed a practical diet without vitamin C supplement for four weeks then stocked in twelve 650-l tanks at 30 fish/tank and fed one of four practical diets containing AMP at 0, 60, 180, or 540 mg/kg dry diet for 17 weeks. Survival rates in all treatments were similar (88.9-98.9%). Fish fed the 0 or 540 ppm diets had inferior final average weights, protein efficiency ratios, and feed conversion ratios than fish fed the 60 or 80 ppm diets (p<0.05). Growth of fish fed the 0 or 540 ppm diets slowed down on day 60 and fish fed the AMP-free diet exhibited clinical signs of vitamin C deficiency with a soft body and a significantly high (p<0.05) hepatosomatic index. Ascorbic acid in brain and liver tissues rose with the level of dietary AMP. Fish fed the 540 ppm diet had significantly lower hematocrit (p<0.05) than fish fed the 60 or 180 ppm diets. Histological analysis of the liver and kidney of fish fed the 180 and 540 ppm diets showed changes indicative of possible toxic effects. Based on growth, feed efficiency, tissue histology, and hematocrit level, AMP at 540 ppm is toxic to snapper. Thus, supplementation of 60 ppm AMP or its equivalent 26 ppm ascorbic acid in practical diets for red snapper promotes optimum growth and feed efficiency and prevents vitamin C deficiency symptoms.

This study was conducted to evaluate the effect on growth and feed efficiencies of the mangrove red snapper (Lutjanus argentimaculatus) when dietary fishmeal is partially replaced by defatted soybean meal (DSM). In the preliminary experiment, snapper (mean weight±SD, 58.22±5.28 g) were fed in triplicate with different dietary amounts of DSM (7.8–42.2%) that were formulated to be isonitrogenous and isocaloric. After 14 weeks, survival, growth and feed efficiencies, and hepatosomatic index (HSI) did not differ. Based on these results, a feeding trial was done using a positive control diet that contained 64% fishmeal, while the other four diets had DSM levels of 12%, 24%, 36%, and 48% that replaced fishmeal protein at 12.5%, 25%, 37.5%, and 50% respectively. All diets were formulated to have about the same protein level (50%), protein to energy ratio (P/E of 25-mg protein kJ−1), and dietary energy (19.8 MJ kg−1). These were fed to triplicate groups of snapper (mean total weight tank−1±SD, 73.19±1.2 g) at 15 fish (average weight, 4.88 g) per 1.5-t tank for 19 weeks. Growth (final average weight and specific growth rate (SGR), feed conversion ratio (FCR), survival, and HSI were not significantly different (P>0.05) while protein efficiency ratios or PERs were similar in treatments with DSM. Among snapper fed DSM, haematocrit value was significantly lower in fish fed 48% DSM and not different with fish fed 36% DSM. Whole-body crude fat of snapper fed 48% DSM was lowest while the crude protein and nitrogen-free extract (NFE) levels were highest. Histopathological analysis showed that lipid vacuoles in livers of snapper were reduced in size as dietary DSM increased. There was slight lipid deposition in the liver of snapper at 36% DSM while at 48% DSM it was excessive and hepatocytes were necrotic. There were no differences in the histology of snapper intestine. Under the experimental condition of thi