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The reduction of the survival of mud crab during culture has been largely attributed to aggressive encounters and cannibalism. In some crustaceans, suppressed aggression is linked to increased concentration of circulating and brain serotonin (5-hydroxytryptamine, 5-HT). Likewise, tryptophan (TRP), a precursor of 5-HT is reported to suppress the aggression and improve the survival of some cultured fish through dietary supplementation. We investigated the effects of feeding formulated diet with different TRP levels (0.32% as control, 0.5%, 0.75% and 1% of dry diet) on the agonistic behavior, growth and survival of juvenile mud crab Scylla serrata. Mud crabs were individually stocked and fed the experimental diets for 4 weeks before they were set to a one hour fight experiment. The fights were recorded using a video camera and the aggressiveness of the crabs was quantified. Hemolymph was sampled after 15 and 30 days of feeding (resting) and right after the fight to measure circulating 5-HT concentration. Higher TRP levels suppressed the aggressiveness of mud crab in a dose dependent manner. The intensity and frequency of attacks were both significantly lower (P l -TRP. The survival of juvenile mud crab can be improved by increasing the level of TRP to 0.5%–1%. However, higher TRP levels may affect growth of mud crab. TRP supplementation resulted to a significant increase of 5-HT concentration in the hemolymph which was clearly observed after the fight suggesting that 5-HT plays an important role in suppressing the agonistic behavior of mud crab during aggressive encounters.

Summary The dietary requirement of tryptophan for juvenile Asian sea bass (Lates calcarifer Bloch) was studied. The juveniles (mean initial weight, 5.30 ± 0.06 g) were given semi-purified test diets containing fish meal, gelatin, squid meal, and crystalline amino acids, for 12 weeks. Each set of isonitrogenous and isocaloric test diets contained graded levels of tryptophan. Fish (15 per tank) were reared in 250-L fiberglass tanks provided with continuous flow-through sea water at 26°C and salinity of 28 p.p.t. Fish were fed twice daily at a feeding rate of 8% of the body weight day−1 for the first 4 weeks and at 3.5–2.5% of the body weight day−1 from 5 to 12 weeks. The experiment was in a completely randomized design with two replicates per treatment. Mean percentage weight gains and feed efficiency ratios were significantly different in fish fed varying tryptophan levels. Survival was 100% in all treatments. On the basis of break-point analysis of the growth response, the dietary tryptophan requirement of juvenile Asian sea bass is 0.41% of the dietary protein. This information will be useful in further refinement of practical feed formulations for the Asian sea bass.

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 this study, DSM can be used in snapper diets at 24% (replacing 25% of fishmeal protein) based on growth, survival and feed efficiencies, and histology of liver and intestine. For a lesser diet cost, an inclusion level higher than 24% DSM is possible with a bioavailable phosphorus supplement.

A feeding experiment was conducted to determine apparent digestibility coefficients for dry matter (ADMD), crude protein (ACPD), crude fat (ACFD), crude fiber (ACFbD), nitrogen-free extract or NFE (ANFED), and crude ash (AAD) of selected feed ingredients for mud crab, Scylla serrata . The nine feed ingredients were Peruvian fish meal, squid meal, Acetes sp., meat and bone meal, copra meal, wheat flour, rice bran, corn meal, and defatted soybean meal. A reference diet (RF) and test diets (consisted of 70% RF diet and 30% of the feedstuff) were used with Cr 2 O 3 as external indicator. The ADMD of the RF and test diets were high except for diet with meat and bone meal. Crude protein, crude fiber, and ash of feedstuffs were digestible in mud crab. Nutrients in squid meal, corn meal, and defatted soybean meal were digested well (ACFbD>95%; ANFED>92%; AAD>71%) compared with nutrients in the meat and bone meal. The AAD of copra meal, wheat flour, rice bran, and meat and bone meal were similar. The ACFD in carbohydrate-rich plant feedstuffs were significantly higher than that in protein-rich animal feedstuffs. For this species, the relative amounts of dietary protein and NFE in feedstuffs had an effect on the ACFD but not on ADMD.

The effect of different dietary protein and lipid levels, and protein to energy (P/E) ratios on growth and body composition of the mud crab, Scylla serrata, was evaluated. Six practical test diets were formulated to contain three protein levels (32%, 40% and 48%) at two lipid levels (6% and 12%), each with P/E ratios ranging from 20.5 to 31.1 mg protein/kJ. Individual crabs were stocked in 36 units of 60-l tanks and maintained on a 40% protein diet until each molted (M0). Newly molted crabs were weighed and fed the test diets until termination at 30 days from the third molt (M3+30). Crabs were monitored daily and body weight (BW) taken after each molt, at intermolt and at termination. Average initial BW (11.18±0.66 g) was taken at 18 days after M0. Carapace width (CW) at M3+30 and of the exuviae (at molt 1, 2, and 3 or M1, M2 and M3), weight of exuviae (M1 to M3), feed conversion ratio or FCR, duration of intermolt, and total number of days of feeding test diets (M0 to M3+30) were determined. At the end of the study, crabs were freeze-dried for analysis of nutrients in the flesh, exoskeleton and fat body. The FCR (3.21–4.21), intermolt duration and total number of days of feeding test diets (111.3–131.2 days) were not affected by dietary treatments (P>0.05). Analysis of covariance was used with CW at M1 and BW at M0+18 as covariates. CW in the 40% protein with 6% lipid or 40/6 diet (P/E ratio, 27.5 mg protein/kJ) did not increase when lipid was increased to 12% (40/12), and it was significantly wider than crabs fed the 48/6 and 48/12 diets (P/E ratios, 31.1 and 27.2 mg protein/kJ). CW and BW did not differ in the 40% and 32% protein diets and were not affected by dietary lipid level at every level of protein. Ca in the exoskeleton was lowest in the 32/6 diet, while exuviae weight was about one-fourth of BW. Crude fat in the lipid deposit of crabs fed 48% protein diets were low. Results showed that the mud crab, S. serrata, grow well when fed diets containing 32–40% dietary protein with either 6% or 12% lipid at dietary energy ranging from 14.7–17.6 MJ/kg.

The approximate levels of dietary protein and energy that would sustain good growth and survival of the mangrove red snapper Lutjanus argentimaculatus (Forsskal) were determined in two feeding experiments. In the preliminary experiment, six fish meal-based diets were formulated to contain three protein levels (35%, 42.5% and 50%) and two lipid levels (6% and 12%) for each protein, with dietary energy ranging from 14.6 MJ kg−1 to 20.5 MJ kg−1. The protein to energy (P/E) ratios of diets ranged from 20.6 mg protein kJ−1 to 27.5 mg protein kJ−1. Diets were fed for 100 days to triplicate groups of snappers with an average initial weight of 24.8 ± 0.4 g. No significant interaction between different levels of protein and lipid was observed. Survival rates (93.8% to 100%), feed conversion ratios (FCR) (2.61–3.06) and condition factors (K) were not affected by different dietary treatments. Regardless of lipid level, fish fed 50% protein diets had a significantly higher specific growth rate (SGR) than fish fed the 35% protein diets, but not compared with the 42.5% diets (P 0.05). There were no differences in survival rates, protein efficiency ratio (PER) and nutrient composition of snapper flesh. All fish had fatty livers. Results indicated that the diet containing 44% protein with a P/E ratio of 23.3 mg protein kJ−1 was optimum for snapper growth under the experimental conditions used in the study.

The dietary requirement of juvenile Asian sea bass Lates calcarifer Bloch for total sulphur amino acids was studied. Fish (average initial weight of 2.59 ± 0.08 g) were reared in twelve 500 L fibreglass tanks provided with flow-through seawater at 26°C and salinity of 31 p.p.t. for 12 weeks. They were fed semi-purified test diets containing 6.2, 7.2, 8.1, 9.0, 10.8, or 12.6 g methionine kg−1 dry diet and a basal level of 3.1 g cystine kg−1 dry diet. The mean crude protein of the diets (containing defatted Peruvian fishmeal, squid meal, soybean meal, and free amino acid mixture to simulate the pattern of hydrolysed sea bass protein) was 46.02%. The crude fat content of the diets was 10.51% from a 1 : 1 mixture of cod liver oil and soybean oil. Survival was 100% in all treatments. On the basis of the growth response, the total sulphur amino acid requirement of juvenile Asian sea bass was estimated to be 13.4 g kg−1 dry diet (2.9% of protein). Fish fed low levels of l-methionine had significantly lower weight gains and feed efficiency ratios as well as slightly higher hepatosomatic indices. No nutritional deficiency signs were observed other than growth depression in fish fed on diets that were low in methionine. This information is valuable in further refinement of formulations of practical diets for the Asian sea bass.

Growth performance of juvenile seabass (initial mean body weight, 0.90 ± 0.04 g) fed varying carbohydrate and lipid levels were determined using practical diets in a 2 × 3 factorial experiment. Two carbohydrate levels (15 and 20%) and three lipid levels (6, 12 and 18%) at a fixed protein level of 42.5% were tested. Dietary energy ranged from 284 to 412kcal 100g −1 diet. The fish were reared for 12 weeks in 601 flow-through tanks with aeration in seawater at 32%. and at 26.5–29 °C. Higher weight gains were observed in fish fed diets containing 20% carbohydrate with 12 or 18% lipid. Lowest specific growth rate was observed in fish fed the 15% carbohydrate at 6% lipid. Survival was 100% in all treatments. The feed conversion ratios for fish fed 20% carbohydrate at 12 or 18% lipid, and 15% carbohydrate with 12% lipid were best. Specific growth rate and weight gain did not differ at lower dietary lipid (12-6% or 18-12%) despite an increase of dietary carbohydrate indicating a sparing of lipid by carbohydrate as an energy source. Dietary lipid at 18% (1:1 ratio of cod liver oil and soybean oil) seems to be excessive for seabass. Based on this study, we recommend a carbohydrate level of 20% in diets containing lipid levels ranging from 6 to 18%.

The optimum protein-to-energy (P/E) ratio for juvenile sea bass (body weight, 1.34 ± 0.01 g) was determined using practical diets in a 3 × 3 factorial experiment. Three protein levels (35, 42.5 or 50%) and three lipid levels (5, 10 or 15%) at a fixed carbohydrate level of 20% were tested. P/E ratios of the diets ranged from 104 to 157 mg protein/kcal. The fish were reared for 54 days in 60-liter flow-through tanks with seawater at 32 p.p.t. and 29 °C. Fish fed the diet containing 50% protein and 15% lipid (P/E ratio of 125 mg/kcal) showed the highest weight gain and specific growth rate. Those fed the diet with 42.5% protein and 10% lipid (P/E ratio of 128 mg/kcal) showed comparable growth rate and significantly better condition factor, protein efficiency ratio and apparent protein retention. Fish given diets containing 35% protein showed the poorest growth. Those fed diets with 5% lipid regardless of the protein content showed abnormal reddening of the fins, indicating essential fatty acid deficiency. Body fat increased with fat content of the diet and was inversely related to moisture. Fish given the diet containing 35% protein and 5% fat had the lowest body fat content and the highest ash and water content. The diet containing 42.5% protein and 10% lipid with P/E ratio of 128 mg protein/kcal was found to be optimum for juvenile seabass under the experimental conditions used in the study.

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

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

The digestibility of four isonitrogenous practical diets (40% crude protein) containing different levels (5%, 15%, 25% and 35%) of gelatinized breadflour as carbohydrate source were determined for P. monodon (average weight 30–40 g). The digestibility coefficients for protein ranged from 92.8 to 94.3%. Crude fat digestibility ranged from 90.0 to 92.8% and dry matter digestibility from 75.7 to 86.9%. Carcass crude protein was similar in all treatments but carcass crude fat decreased significantly (P0.05) among treatments. However, weight gain and SGR were lowest and FCR was poorest with 35% carbohydrate.

Juveniles of the Asian catfish Clarias macrocephalus (3.6±0.17 g; 78.0±0.09 mm) were fed one of four diets: a laboratory-formulated diet of 18.9% (Diet 1) or 34.2% (Diet 2) protein, a com- mercial feed pellet of 28.9% protein (Diet 3) or a diet of 80% blanched chicken entrails and 20% rice bran (31.7% protein; Diet 4). After 120 days of culture, catfish fed Diet 2 grew significantly better (p0.05). Catfish fed Diet 2 had the highest apparent lipid retention (131.7%). The protein efficiency ratio was lowest (1.3) in Diet 2, but did not differ significantly from Diets 1 and 3. Catfish fed Diet 4 were fatty and had a lower crude protein content. Results suggest that C. macrocephalus fed 34.2% crude protein have a significantly higher weight and total yield. Further, a taste test showed that odor, flavor and appearance did not differ amongst the diets.

Growth and changes in the mid-gut cell morphology of Penaeus monodon juveniles were evaluated after feeding for 35 days with semi-purified diets deficient in water-soluble vitamins. Diets were prepared by deleting one vitamin at a time from the vitamin supplement consisting of cyanocobalamine, folic acid, thiamine, riboflavin, pyridoxine, niacin, choline, inositol and ascorbic acid. Controls were the complete vitamin diet (control diet 1) and the no vitamin diet (control diet 2). Growth rate was poorest for treatment without vitamin supplement and the inositol and choline-deficient diets. Enhanced growth was observed in prawns fed with the riboflavin-deficient diet. All treatments except control diet 1 showed histopathological changes in the mid-gut cells. Detachment or destruction of the epithelial cells were observed in most cases but more severely in treatments without vitamin supplement followed by inositol, choline and vitamin C.

The true digestibility of casein, gelatin, fish meal, defatted soybean meal and Leucaena leucocephala leaf meal was measured in 60- and 175-g milkfish ( Chanos chanos Forsskal) in fresh- and seawater. The diets contained 45% of these feedstuffs and 1.3% of the indicator substance, chromic oxide. The intestinal dissection method was used to collect fecal material. Results showed that the length of time between initial feeding and fish sacrifice did not significantly affect digestibility. Gelatin was the most digestible (90–98%) protein, regardless of size. Casein, defatted soybean meal and fish meal were moderately digestible (50–90%) and digestibility coefficients tended to increase as a function of fish size. L. leucocephala was the least digestible (−10–40%). The digestibility of most of these feedstuffs was less in the anterior than in the posterior intestine, and tended to be lower in seawater than in freshwater. Rate of food movement was similar in both size groups, but was significantly faster when milkfish were in seawater rather than in freshwater. The effect of salinity on digestibility may in part be due to food motility changes necessitated by alterations in osmoregulatory processes when fish are in seawater.