Primary Studies On Growth, Food Composition And Resource Protection Of Odontobutis Obscurus In Taihu Lake In Jiangsu Province

Odontobutis obscurus belongs to Perciformes,Eleotridae, Odontobutis, and widely distributes in Yangtze River, Pearl River, Qiantang River, Minjiang River in China. Odontobutis obscurus live in lakes, rivers, the shallow waters or tranquil waters. Odontobutis obscurus, with ambush feeding habit, belongs to carnivorous fish. Owing to the small body type and low natural production, Odontobutis obscurus have not been paid enough attention in the past. In recent years, more and more attention are called in the terms of their delicious tastes. The population composition, growth, food composition and resource alteration of Odontobutis obscurus in Taihu Lake have been researched in this paper. The main results as follows:There are 109 sample fish, 49 males and 60 females. There are 4 age groups of sample fishes, and most of them are in the age of 1-3.Among these samples, age 1 account for 25.69%, age 2 account for 56.88%, age 3 account for14.68%,and the rest are age 4. Odontobutis obscurus grows evenly, so we can apply the growth equation of Von Bertalanffy to evaluate the growth of dontobutis obscurus, Growth equation of body length is Lt = 20.05[1-e-0.208(t+0.808)], and Growth equation of body weight is Wt = 109.22[1-e-0.208(t+0.808)]3. Inflexion point of body weight and age are ti = 4.47a,Wi = 32.36g respectively. Body weights of sample range from 10g to 20g, much smaller than market standards. This indicates that the fishing tools are irrational, and exists overfishing in Taihu Lake. According to growth characteristics, we suggest that fishing standards be fixed above 13cm of body length and 35g of body weight.In March 2009, 59 fresh samples of Odontobutis obscurus were collected at Dongshan in Taihu Lake, the south of the national protected areas. There are 22 males and 37 females among the samples. Sex ration(♀/♂)was 1.68:1.Body length ranges from5.5 to 15.5cm, with a mean of 9.76 cm. Body weight ranges from 3.63 to 85.97g, with a mean of 21.08g. The height of mouth breach is form 0.4 to 1.9cm, with a average of 0.94cm.The width of mouth breach ranges from 0.6 to 2.4 cm, with an average of 1.27cm. The width of mouth breach and body length showed a linear correlation with the equation y = 4.803x + 2.6837, R2 = 0.7731. The feeding rate of Odontobutis obscurus is 94.92%, the average full of degree is 2.29. In its food composition, Pseudorasbora parva accounts dominantly with appearance rate 47.76%.The data of fish catch by species in Taihu Lake in recent 50 years were collected and analyzed, the results showed that there are 107 kinds of fishes, which belong to 14 formes, 25 classes, 73 categories. They are composed of habitual fish, migratory fish and half-migratory fish. In recent years, because of environment deterioration, human interruption and use of destructive fishing tools and increase of fishing intensity, the number of habitual fish, migratory fish, half-migratory fish and littoral fish decreased sharply. Coilia accounts for dominantly in fishing catch, while economical fishes such as Odontobutis obscurus are decreasing.