Biological characteristics of ruby snapper (Etelis coruscans) from the bottom longlining in the Saya de Malha bank of the Indian Ocean

XU Liu-xiong,LIN Dong-ming,YE Xu-chang (College of Marine Science & Technology,Shanghai Fisheries University,Shanghai 200090,China)

Etelis coruscans;biological characteristics;Saya de Malha bank;Indian Ocean

Etelis coruscans (common English name ruby snapper) is a deepwater species with a depth distribution of 100-450 m. This species is widely distributed throughout the Indo-West Pacific region and most of them are found in the steep drop-off zone surrounding the islands and banks. Due to the reduction of traditional fish resources,Etelis coruscans has become one of the important potential fish species targeted by many commercial fishing fleets because of its high marketing price. With the strict management measures applied in high seas fish resources,such as tuna resources by regional fisheries management organizations,China has paid more attention to potential high sea commercially-valued fish species in order to maintain the sustainable development of its distant water fishery. In 2005,supported by Ministry of Agriculture of China,Lianjiang Deep Sea Fishing Company and Shanghai Fisheries University jointly conducted an exploratory fishing survey on ruby snapper resource in the high seas waters of the Indian Ocean. Based on the biological data of 310 ruby snappers collected from October 2005 to January 2006 by bottom longlining vessels in the Saya de Malha bank of the Indian Ocean,the ruby snapper’s maturity stages of the gonad,sex ratios,fork length (FL) distributions,relationships between fork length and body weight were analyzed by statistic and regression methods. The results indicated that:(1) there were more males than females,and the ratio of males to females was about 2.39∶1 in number;(2) gonad maturity at stages Ⅴ and Ⅵ were dominant with the highest percentage (60.80%) at stage Ⅴ. By separated sex statistic,the highest ratio of gonad maturity of both female and male occurred at stage Ⅴ,with 52.27% and 65.24% respectively,but the ratio of females was distinctly higher than that of males at the gonad maturity stage Ⅵ;(3) the fork length distribution well fit the normal model. The dominant fork length was 683-803 mm,occupying 72.90%,with mean value 747 mm.At the same gonad maturity stage,the mean fork length of female was a little longer than that of male;(4) the relationship between fork length and body weight of ruby snapper could be described as W = 9.439 0×10-6 FL3.081 7,with growth index b slightly higher than that of the same relationships regressed from Etelis coruscans in the Pacific Ocean,indicating that ruby snappers in the Indian Ocean and Pacific Ocean possibely did not belong to the same species,or the habitat environment of ruby snappers in the Indian Ocean might be better than that in the Pacific ocean;(5) the body weight of male ruby snapper was heavier than that of the female when FL was less than 897 mm,while the female had heavier body weight if FL was over 897 mm.