| Clarias gariepinus belongs to Clarias, Clariidae, Siluriformes, which known as Egypt Clarias batrachus, and is originated in the Nile river in Africa. C. gariepinus was introduced into China from Egypt in 1981, and was widely farmed soon. The lack of necessary control consciousness and measures to prevent escaping, abundant water resources and the network water system in south China, warm and humid climate, rich food resources, which help to C. gariepinus rapid growth, reproduction and spread. As the body size is big, and has distinctive ability to hunt, brings potential threat to native fish. C. gariepinus grows fast, easily breeding, has tender meat and ability to resistant low oxygen and temperature, and widely spreaded, which aggravated spread. Due to escape in breeding, C. gariepinus has invaded the Pearl River, the Yangtze River, the Yellow River and other main streams in China, and brings serious ecological threats. But we still lack of the information of distribution and invasion ecology of C. gariepinus, and needs to carry out the corresponding research and summary. By investigating the distribution of C. gariepinus in southern China and collecting samples for biology research, to understand the distribution of population, and grasp age structure, growth and reproduction, and prevent and control spread in future.1. The population status of Clarias gariepinu in main rivers of south ChinaBy surveying Clarias gariepinus in the main rivers of south China, including the Pearl River tributary, Jianjiang River and Tanjiang River, Pearl River Delta, and Nandu River, Hushan Reservoir in Hainan Province, found that all sampling points were longstanding large C. gariepinus wild population. Thus, C. gariepinus has been distributed in natural waters of southern China. All sampling points in addition to Wuzhou and Haikou were found C. gariepinus, who were more than two years old, proves that C. gariepinus can wintering in natural waters. In Jianjiang River and Beijiang River, there were three years old individuals, which further proves that C. gariepinus can wintering in natural waters and settle for long time. There were also a large number of female sexual maturity individuals, which shows that C. gariepinus has the ability of the breeding in nature waters. During April to October in 2014, in Jian jiang River, Beijiang River, Xijiang River and Hainan Province, we also found a large number of juvenile fish, was further evidence that C. gariepinus can realize natural reproduction in natural waters. Above all, C. gariepinus could overwinter, reproduction in nature waters in south China, and has fairly stable populations, which has established natural populations.2. Age structure and growth characteristics of exotic fish Clarias gariepinus in south ChinaTo determine the age structure and growth characteristics of C. gariepinus, sagitta ray sections, body length and weight were examined. These specimens were comprised of 3 age groups ranging from age 1 to age 3. Additionally, the dominated age was age 1, accounting for 60.19 % of the total specimens. The formulas of the relationship between standard body length(L) and total weight(W) for females and males were (2♀= 5.763 ×10-57)2.737(n=87,R2= 0.989), (2♂= 9.239 × 10-52.631(n=122,R2=0.942), respectively which showed that the growth of C. gariepinus was nearly isometric. The growth patterns of C. gariepinus was formulated by Von Bertalanffy growth function listed as follow: = 455.566(1- 1877.1120)-8.036), (2= 1089.19 ×(1-1877.1120)-8.036)2.737 for females and = 475.187(1- 1.480)-0.908), (2=1019.66 ×(1- 1.480)-0.908)2.631 for males. The growth inflection points for females and males were 1.07 and 1.64 respectively when the corresponding standard body length on the growth infection points were 297.75 mm for females and 316.79 mm for males, and the corresponding total weight were 340.08 g for females and 350.88 g for males. Analysis also showed that the growth rate became lower with increasing age, and the younger matured individuals grow faster than the older ones. Our results suggested that C. gariepinus have a large population size with single age structure in South China. Moreover, C. gariepinus population is in the rapid growth period, are likely to burst into a sudden growth in the south China while the will.3. Reproductive biology of exotic fish Clarias gariepinus in south chinaClarias gariepinus began to reproduce in May, could continue to August and concentrated in June and July. The distribution of egg sizes had obvious multi-peak type characteristics. The anniversary change of coefficient of fat and fullness had obvious seasonal characteristics, and had reserved trend with gonado somatic index. The absolute fecundity ranged from 2850 to 605720 eggs with a mean of 234232 eggs, and had positive correlation relationship with body length, weight and age. The relative fecundity varied from 20 to 445 eggs per gram with a mean of 165, and increased with the increase of body length, weight and age before it came stable. Absolute fecundity and relative fecundity were greater than other siluridae fishes. Sex ratio was 1 to 1.12 in breeding season, and had no obvious difference with 1 to 1. The minimum sizes of adult females and males were 2 years old with Ⅳ period gonads, the female was 174 mm in length and 119.5 g in weight and gonado somatic index was 8.50 %, the male was 250 mm in length and 116.2 g in weight and gonado somatic index was 0.45 %. The reproductive group main consisted of 1 and 2 years, the percentage were 42.28 % and 51.68 % respectively, and the recruit population was dominated. The results show that, wild population of Clarias gariepinus in south China had characteristics with continuous batch spawner, highly relative fecundity, small in egg size, low sexual maturity age, which could help establish stable populations. It is necessary to step up monitoring for the wild populations of Clarias gariepinus, and further prevention and control measures should be taken. |
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