Study on some biological characteristics of the soap fish Diploprion bifasciatum in Nha Trang bay Vietnam diploprion bifasciatum in Nha Trang bay viet nam

Abstract

A total of 367 soapfishes were collected from commercial fishing vessels in Nha Trang Bay, Khanh Hoa, Vietnam for this present study in order to better understand biological characteristics and possible applications in aquaculture and conservation of this species. Samplings were conducted from March to November 2014. Among the collected fish 63.2% are female. Morphological measurement and stomach content were carried out for all the collected specimens. Body external morphologies and gonads macroscopic and microscopic were studied to sex each individual. The length-weight equation for this species is (R2 =0.91, n=351). Gonadosomatic Index (GSI) and Condition Factor (CF) were used to determine the spawning season. A clustering process was carried out based on GSI and separated the data in to five groups. From each group, ten random representatives were subjected to histology examination to determine the gonadal development stage. External observation could accurately identified 93% males (N=135) and 87% females (N=232). Macroscopic examination of the gonads could identify female correctly while the transforming stage from female to male could only be identified microscopically. All six stages of oocyte development were found, including transforming stage. The spawning season in likely to be from the end of the year, extend to May. These findings could be applied for the development of seed production technology or fisheries management of this species. Keyword: soap fish, Diploprion bifasciatum, length-weight relationship, spawning season, gonadal development.