| Yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) are epipelagic oceanic species belonging to the family Scombridae,they are found worldwide in tropical and subtropical seas.It's very expensive for its high nutrition in international aquatic products market. It's one of pelagic fishery important fishing object in today's world. Beginning in the 1950s, tuna fishing had a rapidly development, since then has been the most impotant epipelagic oceanic species in the world ocean fishery industry. Our country began to developeand utilize tuna resource in the early eighties and it is china's important fishing object in last twenty years.As important commercial species, yellowfin tuna and bigeye tuna lack systematic and specific biology survey because of its wide distribution. This study sampled 1313 bigeye tuna () and 839 yellowfin tuna.continuously in the East Pacific Ocean (1°36′S～16°15′S,125°32′W～141°58′W)fromJune to December, 2009.Breeding peak time, sex ration size at maturity and maturity stages were studied in the paper.1,The result indicated tha the length of male bigeye tuna varied between 42 and 208 cm, the two dominant length varied between 121 and 130 cm and 151 and 160 cm with percentage of 26, 196 samples and average fork length is 138.4cm. The body weight of bigeye tuna varied between 10 and 150kg, the dominant body weight varied between 21 and 30 kg with percentage of 21, 159samples and average body weight is 48.2kg. Fork length - weight fitting curve is y = 2E-05x2.9564(R2 = 0.967. The GSI of bigeye tuna varied between 0.02 and 0.38 and average GSI is 0.15. The length of female bigeye tuna varied between 78 and 220 cm, the dominant length varied between 121 and 130 cm with percentage of 16, 202samples and average fork length is 138.4cm. The body weight of bigeye tuna varied between 10 and 145kg, the dominant body weight varied between 21 and 30 kg with percentage of 24, 297samples and average body weight is 45.8kg. Fork length - weight fitting curve is y = 1.9412e0.0216x(R2 = 0.9601). The GSI of bigeye tuna varied between 0.03 and 8.98 and average GSI is 2.17. The second half year, gonad index gradually getting bigger to the maximum value (3.97) in Septemb December. By gonad index (GSI) and with the developing of gonad can be deduced that the December is the female bigeye tuna reproductive time in the eastern Pacific. The size of 50% morphometric maturity occurred at 136cm by LoGSItic's return.2,The result indicated that the length of male yellowfin tuna varied between 93 and 185 cm, the dominant length varied between 121 and 130 cm with percentage of 32, 329samples and average fork length is 132cm. The body weight of male yellowfin tuna varied between 10 and 80kg, the dominant body weight varied between 26 and 30 kg with percentage of 28, 285samples and average body weight is 28kg. Fork length - weight fitting curve is:y = 6E-06x3.1801,R2 = 0.9279. The GSI of yellowfin tuna varied between 0.04 and 2.62 and average GSI is 0.56.The second half year, gonad index first become smaller and smaller to the minimum value (0.41) in September, and then gradually getting bigger to 5.17 in December. The length of female yellowfin tuna varied between 23 and 177 cm, the dominant length varied between 126 and 130 cm with percentage of 19, 116samples and average fork length is 129cm. The body weight of yellowfin tuna varied between 10 and 90kg, the dominant body weight varied between 26 and 30 kg with percentage of 27, 139samples and average body weight is 31kg. Fork length - weight fitting curve is y = 7E-06x3.1335(R2 = 0.8966). The GSI of yellowfin tuna varied between 0.05 and 5.17 and average GSI is 0.86.The second half year, gonad index first become smaller and smaller to the minimum value (0.61) in July, and then gradually getting bigger to the maximum value (5.17) in September. By gonad index (GSI) and with the developing of gonad can be deduced that the September is not the female yellowfin tuna reproductive time in the eastern Pacific. The size of 50% morphometric maturity occurred at 108.55cm by LoGSItic's return.3,For each ovary, the oocytes in the most-developed mode were categorized into 7 stages: proliferation, growing, partially yolk globule, fully yolk globule, migratory nucleus, hydrated. The histological analyses of ovaries were used to estimate the maturity and reproductive activity stages for individual females. Females were classified as proliferation, growing, maturation, ovulating and post-ovulation stage according to its oocyte development according to the oocytes development. 4,Histological evaluations of cross sections showed that the testis structure of yellowfin tuna and bigeye tuna are classified as the"unrestricted spermatogonial"testicular type, based on the location of spermatogonia within the germinal epithelium. The testis consists of two structurally different regions, an outer proliferative region where germ cells develop synchronously in cysts, and a central region made up of a well-developed system of ducts that convey the spermatozoa produced in the proliferative region to the main sperm duct which is from seminal vesicle .The TS was observed at all males except immature.Testis development in two tuna were categorized into 5 stages: proliferation, growing, maturation, releasing sperm and regression stage。... |
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