Experiments Of Flatfish Culture Using Two New-style Net Cages And Effect Of Farming Density On Paralichthys Olivaceus

The net cage culture for flounder plays an important role in cage culture. Due to the particularity of flounder net cage culture, it has rarely been studied in domestic. At the same time, both the cage facilities and farming technology need to be improved. The flounder net cage culture came across a series of industrial problems in particular sea area. In this paper, we firstly designed two kinds of new-style cages made of environment-friendly plastic and they were used in the aquaculture experiments for a period of time. During the farming process, some indicators of Paralichthys olivaceus and Scophthalmus maximus(turbot) were measured. These two kinds of new-style cages were designed to solve the problems such as marine environment pollution, highlydensity of cage facilities, low breeding density per unit water area and other problems caused by the traditional cage aquaculture. Then, the breeding density effect of Paralichthys olivaceus in net cage culture was evaluated. Indicators such as growth, nutrition, biochemistry of Paralichthys olivaceu were measured under different breeding density in order to explore the effect that on Paralichthys olivaceus. The results and conclusions are summarized as follows:1.Two kinds of new-style cages made of environment-friendly plastic which had monolayer-cage and bilayer-cage respectively were developed based on Paralichthys olivaceus and Scophthalmus maximus culture. And the culture effects were tested according to the actual culture experiments. In the Paralichthys olivaceus culture experiments, the traditional wooden cage group had a survival rate of 92.7% with a yield of 16.4kg/m~2, while the new monolayer plastic cage group had a survival rate more than 96% with a yield up to 17.4 kg/m~2. There were significantly difference in the two cage groups(P<0.05)about survival rate and yield per unit area. While the yield per unit area of the new monolayer plastic cage group was 6.1% higher than that in the traditional wooden cage.In the Scophthalmus maximus of small size culture experiments, the traditional wooden cage group had a survival rate of 92.5% with a yield of 8.1kg/m~2, while the new monolayer plastic cage group had a survival rate of 92.5%, and the bilayer plastic cage group had a survival rate of 92.0% with a yield of 10.5kg/m~2. It had significantly difference in the yield per unit area relative to the traditional wooden cage group and the monolayer plastic cage group(P<0.05). While the yield per unit area of the new bilayer plastic cage group were 30.0%and 31.3%higher than that of the traditional wooden cage a. In the Scophthalmus maximus of big size culture experiments, the survival rate was more than 95% and the yield was between 14.5and 16.3 kg/m~2 in both two new-style plastic cage groups. There was significantly difference in the aspect of average weight of fish released between the two new plastic cage groups(P<0.05). while the yield per unit area of double-layer cage group was 11.0% higher than that in monolayer cage. The results demonstrated good validity in flatfish culture using new plastic environment-friendly cages. Compared with traditional wooden cage, the newtype plastic cage has advantages such as energy-saving, environment-friendly and operation-convenient. Especially, the double-layer plastic cage can promote the effective use of area, increasing the culture benefits.2.In order to study the effects of different breeding density on flounder(Paralichthys olivaceus) in cage culture, three different density were designed and they were 800(group A), 1000(group B) and 1200(group C), respectively. The effects were evaluated by the results of breeding process, the nutrition index and serum biochemical indexes. The results showed that average body weight, survival rate, growth rate and daily mean body weight increment of bastard halibut all decreased significantly with the increase of breeding stock density(P<0.05). The stock density had no significant effect on fish ingredients, types and contents of amino acid and types of fatty acid(P>0.05). The percentage of EAA/TAA and EAA/NEAA decreased significantly with the increase of stock density(P<0.05). Under high stock density condition, the contents of glucose(GLU) and thyroid(T4) hormone in serum of bastard halibut were significantly decreased(P<0.05), while the contents of total cholesterol(TC) were significantly increased(P<0.05). The activities of alkaline phosphatase(AKP), glutamic pyruvic transaminase(ALT) and aspartate aminotransferase(AST) were in state of significantly higher. The experiment results indicated that the stock density had significant effects on cage culture of bastard halibut. According to the results in this paper, the stock density of cage culture should be increased properly rather than be blindly expanded in the production practice.