Mean Initial Wet Weight Research Articles

Effect of dietary phosphorus sources and varying levels of supplemental phosphorus on survival, growth and body composition of postlarval shrimp (Litopenaeus vannamei)

Two experiments were conducted for 30 days each to investigate the effective phosphorus source and supplemental phosphorus levels for postlarval Litopenaeus vannamei. The first experiment was performed in postlarval shrimp (mean initial wet weight 2 mg) fed four isoenergic and isonitrogenous diets containing three supplemented inorganic phosphorus sources [D1: no supplemental phosphorus, D2: NaH2PO4·2H2O, D3: KH2PO4·2H2O, D4: Ca(H2PO4)2·2H2O]. The quantities of the three supplemental NaH2PO4·2H2O, KH2PO4·2H2O and Ca(H2PO4)2·2H2O were 11.6, 12.8 and 10 g kg−1 of the diet, respectively in order to make the three diets have the same total phosphorus. Growth performance (final mean body weight, FBW; weight gain, WG; specific growth ratio, SGR) of shrimp in D3 treatment was the highest and had significant difference with the D1 treatment. The survival of shrimp in D3 treatment was the highest and had significant difference with the other treatments. The mineral concentration and body composition of shrimp were not significantly different among treatments. We could conclude that KH2PO4·2H2O was the optimal phosphorus source for postlarval L. vannamei from the growth performance and survival. The second experiment was performed in postlarval shrimp (mean initial wet weight 0.88 mg) fed four isoenergic and isonitrogenous diets containing four supplemental KH2PO4·2H2O levels (d1, d2, d3 and d4 with 0, 5, 10 and 20 g kg−1, respectively). Shrimp in d2 treatment showed the highest growth performance and survival and also showed significant difference with other diet treatments. The whole body content of zinc (Zn) increased with the increase of dietary KH2PO4·2H2O and significant differences were observed when dietary KH2PO4·2H2O reached 5 g kg−1, excess KH2PO4·2H2O supplementation (10 and 20 g kg−1) had a negative effect on Zn content, the Zn content significantly decreased when KH2PO4·2H2O was 20 g kg−1. We can conclude that the amount of total phosphorus in the diet should be maintained between 20.9 and 22.0 g kg−1, the amount of supplemental KH2PO4·2H2O in the diet is less than 10 g kg−1.

Effects of stocking density on behavior and growth rate of European sea bass ( Dicentrarchus labrax) juveniles reared in a closed circulated system

Four duplicated groups of sea bass juveniles (mean initial body wet weight 6.6±1.1 g and mean total length 8.56±0.52 cm) were reared under closed circulated water system conditions at different stocking densities (80, 165, 325 and 650 specimens/m 3) for 168 days. The aim of the experiment was to determine the general behavior and the effect of fish stocking density on fish growth, feeding and metabolism during the critical period of the first 6 months of the commercial life of sea bass. Statistically significant differences ( P<0.05) for final fish weight were observed between groups of the two highest and the lowest stocking densities. The highest specific growth rate and the lowest food conversion ratio were observed for fish of the highest stocking density. No statistically significant differences ( P<0.05) were found in haematocrit values, while no meaningful statistical differences were found in hepatosomatic indices in the groups of fish held at any stocking density. Significant differences in water quality among treatments was observed, with relatively poorer water quality occurring at the higher fish densities. The results suggest that schooling behavior of the sea bass may have been a factor in the observed differences in fish performance. However, no formation of clear dominance hierarchies was observed. It is concluded that sea bass, within the range of stocking densities tested and at least at its early stages, does not belong to that fish category which is characterised by an inverse correlation between stocking density and growth rate.

The effect of dietary lipid level on variation of flesh pigmentation in rainbow trout ( Oncorhynchus mykiss)

Variation in flesh pigmentation was assessed in rainbow trout fed different dietary lipid levels. Triplicate groups of 80 rainbow trout with a mean initial wet weight of 54±1 g were fed on pigmented fish meal-based diets containing 8.2% (A), 17.7% (B) or 26.7% (C) crude fat for 25 weeks. All diets contained synthetic astaxanthin concentrations ranging from 43.7±0.9 μg/g to 49.7±0.8 μg/g. The chromaticity of the dorsal, belly and tail regions of the fillets was assessed every 40 days by Minolta Chroma Meter and the astaxanthin concentrations determined by high performance liquid chromatography. At each sampling, the tail regions within all treatments had significantly higher concentrations of astaxanthin and a * values, than the dorsal and belly fillet regions, although among treatments, there were no significant differences in carotenoid content. At each sampling, the coefficient of variation of fillet pigmentation between the different fillet areas was not significantly different within and among the dietary treatments. The flesh astaxanthin concentrations ranged from 0.23 μg/g in the fish at the start of the experiment to 13.1 μg/g in the tail region of fish fed diet A with final flesh astaxanthin retention coefficients ranging from 11.6% in fish fed diet A to 14.9% in fish fed diet C. Fillet lipid content ranged from 2.3% in the tail musculature of the initial trial fish, to 10.3% in the belly muscle of fish fed diet C. Significant negative correlations were found between fillet lipid content and astaxanthin concentration in fish fed diets A and B. Colorimetry measurements demonstrated large variations in fillet colour irrespective of dietary treatment. Tristimulus chromometer a * values ranged from 4.83 to 25.96, b * values from 7.23 to 31.33, L * values from 34.72 to 63.39, while chroma and hue values ranged from 8.47 to 39.89 and 34.12° to 72.33°, respectively. In all treatments, L * values were significantly correlated with flesh lipid content, however, only the a *, b * and chroma values of fish fed diet A were significantly correlated with flesh lipid content. Although the flesh deposition efficiency of astaxanthin increased with increasing dietary lipid level, this did not reduce the amount of variation in fillet pigmentation observed within and among treatments over the experimental period.

Nutritional Evaluation of Dietary Soybean Protein for Juvenile Freshwater Prawn Macrobrachium rosenbergii.

A feeding trial was carried out to evaluate the nutritive value of soybean protein (SBP) for the juvenile freshwater prawn Macrobrachium rosenbergii (0.1g mean initial wet weight) compared with crab protein concentrate (CPC). Protein contents of the test diets ranged from 30 to 55% with an interval of about 7% and the dietary energy was kept constant (4.3 kcal/g) by adjusting carbohy-drate contents (α-starch and dextrin). Although the weight gain of CPC diet groups seemed to be higher than that of SBP diet groups at each protein level, no statistical significance was detected between SBP and CPC diet groups, with the exception of the prawns fed on the diet containing the second highest protein level (about 47%). There was a tendency for feed conversion efficiency (FCE) and protein efficiency ratio (PER) of SBP diet groups to be better than those of CPC diet groups in each protein level except for prawns fed on the second highest protein level (about 47%). The results above demonstrated that SBP could be a useful protein source for Macrobrachium diets. Protein levels tested in this study did not affect the growth, FCE, or PER in either CPC or SBP diet groups, which indicates the possibility of protein sparing by carbohydrate in M. rosenbergii. The proximate composition and amino acid pattern of the whole body were not affected by protein sources or levels.

Effects of Unilateral Eyestalk Ablation and Feeding Frequencies on Growth, Survival, and Body Compositions of Juvenile Freshwater Prawn Macrobrachium rosenbergii.

A feeding trial was conducted to examine the effects of unilateral eyestalk ablation (UEA) and feeding frequencies on the growth, survival, and chemical compositions of whole body for the juvenile freshwater prawn Macrobrachium rosenbergii (0.1g mean initial wet weight) fed on a carb protein-based diet. The results demonstrated that UEA promotes the growth and the ablated prawns are able to reach commercial size (30g) 40 days earlier than intact ones. Although feeding frequencies did not affect the growth and survival of juvenile prawns significantly, ablated prawns fed twice a day produced the best results. In intact groups, feeding once a day was good enough to sustain optimal growth in the present study. Neither UEA nor feeding frequency affected the con-tents of protein, lipid, or the compositions of lipid class and fatty acid of prawn whole body. Major neutral and polar lipids were triglyceride and phosphatidylcholine, respectively, and high levels of 16:0, 18:1 and 18:2n-6 were found in whole body of both ablated and intact prawns.

Some effects of oral doses of oxytetracycline on growth, survival and disease in Penaeus aztecus

Two size groups of brown shrimp ( Penaeus aztecus) were fed a formulated feed containing 0, 100, 1 000 or 5 000 mg of oxytetracycline/kg of feed. Growth and survival were measured after a 3-week drug consumption period. The shrimp were then inoculated with Vibrio alginolyticus, and survival was monitored during the following 24 h. At all three concentrations of oxytetracycline, small shrimp (mean initial wet weight 143.4 mg) consumed approximately one-third the amount of feed consumed by those fed the control diet with no oxytetracycline, yet growth was more rapid with diets containing 100 and 1 000 mg of oxytetracycline/kg of food than with the control diet. Larger shrimp (mean initial wet weight 458.1 mg) receiving oxytetracycline consumed about one-fourth the feed consumed by those on the oxytetracycline-free diet. Some growth inhibition was apparent in these shrimp at all oxytetracycline concentrations. Maximum drug consumption rate, based on actual feed intake, was approximately 1 300 mg oxytetracycline per kg body weight per day for small shrimp, but only 370 mg per kg body weight per day for larger shrimp. All shrimp fed 0, 100 or 1 000 mg of oxytetracycline/kg of feed died within 24 h following inoculation with a standard dose (70% light transmission at 520–540 nm) of Vibrio alginolyticus. All the small shrimp and 70% of the large shrimp fed at the 5 000-mg drug level died, but death generally took place later in the 24-h period than with those fed at the lower drug concentrations. All shrimp fed 5 000 mg oxytetracycline/kg of feed and inoculated with a 1 : 100 dilution of the standard dose of Vibrio alginolyticus survived. All small shrimp and 90% of the large shrimp survived injection of sterile saline.