| With the quickly development of aquiculture in China, more and more foreign species were introduced to the culturist. The introduced species may cause potential threaten to the local natural zoology and the local biology diversity because of lacking corresponding risk evaluation before introducing and because of not well studying their biological and ecological characters. The Sciaenops ocellatus was introduced and the aquaculture had formed largish scale for their characters of adapting better, growing faster and resisting well. However, the number of escaping Sciaenops ocellatus to the natural sea area was increasing day by day. It would cause negative influence on the zoology of the sea in case of the escaping Sciaenops ocellatus forming population and reproducing more. In this paper, several aspects were studied as follows to evaluate their influence on the local zoology of natural sea. All the results offer theoretic gists for the scientific decisions and have important significance for protecting the sea zoology environment and the biology diversity of Zhejiang and the east sea area.1. Investigate the actuality of cultured Sciaenops ocellatus in the net and their escapingAfter investigating the correlative data, comparing the primary environment of Sciaenops ocellatus and the environment of Zhejiang sea area, comparing the adapting ability of themselves, we found the natural sea condition of Zhejiang sea area adapt to the growth of the Sciaenops ocellatus, the fish can reach their maturity and reproduce. But more investigation should be done to assure if they can form population.By investigating each fishing village and key county of cultivation along the sea of Zhejiang, we found out the culture of Sciaenops ocellatus in net and their escaping in Zhejiang sea area, including sea area, number and size. We set up purchase spots to found out the moving, distributing and number of the escaping fish in the natural sea area.All the results showed that there are millions of Sciaenops ocellatus in all escape along Zhejiang sea area since they were introduced in 1995. The escaping fish distribute along Zhejiang sea area or off the sea. They had formed some scale and caused potential threaten to the local natural zoology and the local biology diversity2. Investigate the growth and reproduce characters of the escaping Sciaenops ocellatus in the local sea areaGathering the captured Sciaenops ocellatus in the natural sea area from the purchase spots, we investigated the size, weight, age, development of gonad and reproduce and we also investigated the distributing of the spawn and the larva of Sciaenops ocellatus. Based on the biological characteristics data of 156 ind samples collected in the sea area of Zhejiang in 2004-2006, the results were as follows:(1) Analyzing the relationship of the measurable characters. We obtained the relationship of span-length, weight-net weight, length-weight. Comparing the results with predecessor's, we think that Sciaenops ocellatus in the sea area of Zhejiang, is very similar with the population in the American sea area.(2) Authenticate the age with the stone and by the software of FiSTA II we obtained the growth equation of von-Bertalanffy(BL∞=951.09 mm, k=0.27, t0=0.57;TL∞=1 144.61 mm, k=0.26, t0=0.52; WB∞=14 468.07 g, tx=4.514,Φ′BL=5.388) and body index(Q=1.82). Compared the growth of Sciaenops ocellatus under different zoology environment, the results showed that it has adapted well to sea area of Zhejiang, which is very similar with growth characteristics in the American sea area. Once the Sciaenops ocellatus reproduce massively, it will threat to the endemic species.(3) Analyzing the maturity of the gonad. The maturity of the Sciaenops ocellatus in natural sea area of Zhejiang can reachⅤstage. Sciaenops ocellatus at the stage ofⅢappear in month of 7 and 8 in the sea area and can be captured at the stage ofⅤin month of 9 and 10. It is considered that Sciaenops ocellatus at the stage ofⅤcan reach mature and spawn at the natural condition and the spawn top is in month of 9 and 10. The younger mature Sciaenops ocellatus captured is at the age of 4. In addition, based on the investigative data of the distribution of spawn and larva at Sep. and Oct. in 2006, we didn't find oosperm, larva of just hatch and parr under 10 cm. It is considered that the escaping Sciaenops ocellatus hadn't form reproduced population in the natural sea area.(4)Analyzing the eggs number of female escaping Sciaenops ocellatus at the age ofⅣ-Ⅴ. The results showed that the average eggs number is 100-200 million at the age of 4-6 with the weight of 4 00-8 500 g. Because of not capture enough mature individuals, the results only indicate that the Sciaenops ocellatus can reach mature stage in the natural sea area of Zhejiang.3. Study on the stomach content of Sciaenops ocellatus in Zhejiang sea areaBased on the investigative data of stomach content, the food composition, the feeding ecological type, the feeding intensity and the trophic level of the escaping Red Drum in Zhejiang sea area were studied. The results showed that the Red Drum belongs to nektivorous fishes. It's mainly feeding on Pisces, Macrura, Brachyura , Cephalopoda and also Stomatopoda, Polychaeta. The food composition and the feeding ecological type have obvious differences with that of primary habitat. The feeding intensity of Red Drum, the highest full coefficient in stomach and the average accounting for 80.28 %, 60.93‰and 10.26‰respectively. According to calculation, the feeding niche breadth ranges and the trophic level is 4.09 and 3.43 respectively. The Red Drum in Zhejiang sea area is a kind of raptorial middle carnivorous. |
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