Viscerasomatic Index Research Articles

Optimum feeding rates for European sea bass Dicentrarchus labrax L. reared in seawater and freshwater

Growth, feed conversion efficiency, fillet composition and morphological indices of European sea bass (initial weight of 2.6±0.3 g) were investigated in a 6×2 factorial designed experiment employing two salinities [seawater (SW, 40 ppt) and freshwater (FW, 0.4 ppt)] and six different feeding rates (2.0%, 2.5%, 3.0%, 3.5%, 4.0% of their body weight (bw) day −1 and to satiation) for 60 days. Twenty fish were stocked into 155-l round tanks and each treatment had three replicate tanks. Throughout the experiment, weight gain and specific growth rate (SGR) were highest at ration 4.0 bw day −1 and to satiation in SW group. Regardless of feeding rate, sea bass fingerlings grew about 20–30% more in SW than those reared in FW. There was a significant ( P<0.05) interactive effect of feeding rates and culture media (SW and FW) on weight gain and feed conversion efficiency (FCE). FCE was found to be lower in fish fed to satiation (65–66%) compared to the feeding rate of 3.5% bw day −1, which was best in both SW (89.1%) and FW (86.5%). There were no significant differences in either protein or ash contents of the fish cultured in SW or FW although lipid and moisture contents changed with increasing feeding rate. Condition factor, fillet yield and carcass/body weight were significantly increased, whereas hepatosomatic index, viscera somatic index decreased when the feeding rate was increased above 2.0% bw day −1. Feeding rate proved to be the main differentiating factor in all growth, FCE and fillet composition parameters. Values of SGR plotted against feeding rates allowed the maintenance, optimum and maximum feeding levels to be determined. Based on the calculations, the optimum feeding rate for sea bass fingerlings (3 g) reared in SW and FW is 3.0% and 3.5% bw day −1, respectively. In addition, the optimum feeding rate for FCE was calculated as 2.7% bw day −1 in SW and 3.8% bw day −1 in FW. It is concluded that growth and FCE of European sea bass can be improved by feeding them at about 3.0–3.5% bw day −1 in SW or FW.

Effects of 3,5,3 -triiodo-L-thyronine (T3) and 6-n-propyl-2-thiouracil (PTU) on growth of GH-transgenic coho salmon, Oncorhynchus kitsutch

GH-transgeniccoho salmon (Oncorhynchus kitsutch) juveniles were fed diets containing 3,5,3′-triiodo-L-thyronine (T3; 30 ng/g fish) or 6-n-propyl-2-thiouracil (PTU; 20 ug/g fish), to assess the effect of these drugs on the physiology, growthand survival in comparison with untreated transgenicand non-transgenic salmon. After 84 days, food intake, feed efficiency, survival, growth, hepato-somatic index (HSI), viscera-somatic index (VSI), plasma L-thyroxine (T4), T3and growth hormone (GH) levels,and cranial morphological abnormalities were determined. Growth of transgenic salmon was significantly faster than the nontransgenic salmon,and was increased by exogenous T3and reduced by PTU. Food intake of transgenic salmon was higher than that of the nontransgenic group, but was reduced by exogenous PTU administration. Food conversion efficiency of transgenic salmon was lower than that of nontransgenic salmon,and also was increased by T3 but reduced by PTU in the transgenic fish. The survival rate in all transgenic groups was significantly higher than that of nontransgenic,and transgenic T3and PTU treatment groups showed higher survivals than the transgenic-control group. The HSIand VSI of the transgenic fish were higher than the nontransgenic fish;and both parameters in the transgenic salmon were increased by PTU, but reduced by T3. The plasma T4 level in transgenic salmon was approximately 1.5-fold higher relative to the nontransgenic fish, whereas no difference was observed among the transgenic groups. Plasma T3 levels in transgenic salmon were also approximately 2-fold higher relative to the nontransgenic fish. However, the plasma T3 level in transgenic animals was increased by exogenous T3 administration, but was reduced by exogenous PTU to that observed in nontransgenic salmon. The plasma GH level of transgenic fish was higher than that of the nontransgenic salmon,and the level was increased by the exogenous T3, whereas exogenous PTU did not reduce significantly GH levels in transgenic salmon. Transgenic fish also displayed cranium, jawand opercular abnormalities typical of the effects of this gene construct incoho salmon, indicating that some imbalance in growth processes has been induced. However, these abnormalities (especially cranial disruptions) were diminished by administration of exogenous PTU. In conclusion, exogenous T3and PTU treatments can induce hyperthyroidismand hypothyroidism, respectively,and have inverse effects on growthand skeletal abnormalities of transgenic salmon constitutively expressing GH.

Growth and nutritional trials on transgenic Nile tilapia containing an exogenous fish growth hormone gene

In a long-term growth trial, transgenic tilapia Oreochromis niloticus L. showed a 2·5-fold increase in growth compared with non-transgenic siblings. At 7 months, mean mass of transgenic tilapia was 653 g compared with 260 g for non-transgenic siblings. A significant increase (P >0·01) in head: total length ratio, viscera-somatic index and hepato-somatic index was observed in transgenic fish. Female gonado-somatic index (I G) was found to be lower in transgenics than non-transgenic siblings in both mixed and separate culture conditions. Transgenic male I G values were found to be higher in mixed culture and lower in separate culture than that of their non-transgenic siblings. Food conversion efficiency was more than 20% greater in the transgenic fish. In a second shorter-term growth performance trial, the transgenic fish grew to about four times the size of their non-transgenic siblings. A digestibility trial suggested that transgenic tilapia were more efficient utilizers of protein, dry matter and energy. Apparent digestibility of protein and apparent energy digestibility were higher in the transgenic fish.

Growth and nutritional trials on transgenic Nile tilapia containing an exogenous fish growth hormone gene

In a long‐term growth trial, transgenic tilapia Oreochromis niloticus L. showed a 2·5‐fold increase in growth compared with non‐transgenic siblings. At 7 months, mean mass of transgenic tilapia was 653 g compared with 260 g for non‐transgenic siblings. A significant increase (P &gt;0·01) in head: total length ratio, viscera‐somatic index and hepato‐somatic index was observed in transgenic fish. Female gonado‐somatic index (I G) was found to be lower in transgenics than non‐transgenic siblings in both mixed and separate culture conditions. Transgenic male I G values were found to be higher in mixed culture and lower in separate culture than that of their non‐transgenic siblings. Food conversion efficiency was more than 20% greater in the transgenic fish. In a second shorter‐term growth performance trial, the transgenic fish grew to about four times the size of their non‐transgenic siblings. A digestibility trial suggested that transgenic tilapia were more efficient utilizers of protein, dry matter and energy. Apparent digestibility of protein and apparent energy digestibility were higher in the transgenic fish.