Biology And Distribution Characteristics Of Three Middle - Level Fish In Slope Waters Of The South China Sea

Mesopelagic fishes inhabit the ocean mesopelagic zone, ranged between 200 and 1,000 mete-rs in depth. Most of mesopelagic fishes are micronekton fishes, which characterized by rapid growth,early sexual maturity and diurnal vertical migration. They are the key species linking primary consumers like copepods, euphausiids and top predators like squids, whales and pengui-ns in a typical food web. However, in the past few decades, traditional fishing and processing technology limited the development of mesopelagic fishery. With recent development of survey technology, the great biomass of mesopelagic fish and the important role they play in ocean foo d web and carbon cycles aroused extensive scientific and commercial interest. In this paper, we trie to briefly review the biomass distribution, biology characteristics, utilization, ecological role of mesopelagic fish and future outlook.The Ceratoscopelus warmingii was important species in the catches of mesopelagic fish survey conducted in the northern slope of the South China Sea during June 2015.The biological characteristic of C. warmingii have been studied. In this study, the length of C. warmingii are ranged from 30 to 64 mm and the population was trimodal with three overlapping length groups.The relationship between standard length and weight is:W=8.418×10-6L3.0985. For reproductive biology of this study: over half of C. warmingii the in June collections were at maturity stage II and maturity stage III, the sex ratio was 1:0.70(females: males), males were smaller than females,C. warmingii attained sexual maturing of 50% at 42.54 mm SL.During night the average degree of stomach fullness of C. warmingii increase with time. More systematic sample collection at different depth will helps to analyze the biology of C. warmingii.Chauliodus sp. and Polyipnus sp. were important species in the catches of mesopelagic fish survey conducted in the northern slope of the South China Sea during June 2015.The biological characteristic of Chauliodus sp. and Polyipnus sp. have been studied. In this study, the length of Chauliodus sp. are ranged from 65 to 243 mm. The the weight of Chauliodus sp. are ranged from1.72-10.7g. The relationship between standard length and weight is:W=8.418×10-6L3.09853. The length of Polyipnus sp. are ranged from 31—59mm. The the weight of Chauliodus sp. are ranged from 0.49 to 32.32 g. The relationship between standard length and weight is:W=1.36313×10-4L2.715566. The major degree of stomach fullness of Chauliodus sp. were stage I and stage III. More systematic sample collection at different depth will helps to analyze the biology Chauliodus sp. and Polyipnus sp.Understand the distribution feature of C. warmingii is important for knowing the ecosystem of the northern slope of the South China Sea. Based on the trawl and environment data, the distribution,the fishing ground gravity and the relationship of the distribution and environment factor have been studied. In this study, above 600 m, no C. warmingii were collected during the daytime. During the night, C. warmingii were collected above 650 m except one station. This distribution pattern agree with the other research result that the diel vertical migration is one of important feature of C. warmingii. and during day time most species aggregated in water deeper than 700 m depth. Compare with summer 2015 the fishing gravity of autumn 2014 was shifted southward. The trawl catches of C. warmingii may related with time、the temperature and the dissolved oxygen of the trawling depth.The Chauliodus sp. was important of mesopelagic fish. Based on the trawl and environment data, the distribution,the fishing ground gravity and the relationship of the distribution and environment factor have been studied. In this study, most Chauliodus sp. were catched in the depth below 400 m. Only two station catched some Chauliodus sp. at depth about 70 m. Based on the GAM model,the trawl catches of C. warmingii may related with the depth 、 trawling depth 、 time 、 the temperature and the dissolved oxygen of the surface water.