EFFECT OF STOCKING DENSITY ON GROWTH,FEED CONVERSION AND PIGMENTATION IMPROVEMENT OF TURBOT (SCOPHTHALMUS MAXIMUS L.)

Turbot Scophthalmus maximus L. is a flatfish species distributed along east and north coasts of Atlantic Ocean in nature. It was first introduced to China in 1992 by the Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences. Since then many researches have been carried out for taming, seed breeding and culture. At present, turbot is an important culture species in China and contributes greatly to economy and society. Higher density stocking could utilize water resource completely and promote production. However, high density would affect behavioral interactions then consequently the growth rate showing up pigmentation abnormal. Very low density would waste water and energy. This study discusses the effect of stocking density on growth, pigmentation improvement and feed coefficient of turbot and search for the most suitable stocking density in turbot culture. In our experiment, juvenile turbots were reared in five different experiment groups with initial stock density of 0.28, 0.87, 1.12, 1.16, and 2.75kg/m2 respectively. At the experiment end 60 days later, the stock density was 1.91, 6.31, 8.86, 11.97, 17.67kg/m2 respectively. Special growth rate are calculated using SGR (Special growth rate) = 100×(lnWe-lnWi)/t. Coverage of the tank bottom in percentage at the ending time of the experiment is estimated for all the treatment groups as well as in growth variation, growth rate, survival rate and pigmentation improvement. Results show that, under the same ambient condition, the stocking density has positive effect on growth at low density and negative at high density. SGR was 3.189, 3.304, 3.447, 3.341, and 3.087 respectively for each group. SGR is positively related to low stocking density but to high stocking density. SGR in early stage (0—30days) is higher than late stage SGR (30—60days), according with the law of growth in biology. The uniformity of weight distributing among the groups was decreased with increasing density. The highest density group corresponded to the largest weight range, and vise versa. The stocking density is positively related to feed coefficient. For example, Group 1 that in the lowest density has the least feed coefficient 0.96. Similarly for Group 5, the highest 1.25. The other 3 groups were in between. High density inhibits the animal from growing and also increases the feed coefficient. For survival rate, the result shows that the experiment condition satisfied the need for turbot surviving. No significant difference was shown among the groups. For pigmentation improvement, turbots in albinism were chosen. They were fed with the same filtered quality synthetic feed. Pigment was shown first on the surface of the internal organs then spread over their body as they grow up. Best pigmentation improvement was found in Group 3 whose retrieval rate of complete natural pigmentation was 22%, comparing to the least one, 10% in Group 5. This result shows that pigmentation improvement was slightly affected by stocking density negatively. The suitable stocking density would be helpful to pigmentation improvement. However, the stock density is not the only one factor that affects pigmentation improvement. Other factors especially nutrition and seed quality are also important ones to which follow-up research needs to be done.