Chinese gizzard shad, <i> Clupanodon thrissa </i>, biological characteristics, Hai Phong, Van Uc estuary.
Keywords:Chinese gizzard shad, Clupanodon thrissa, biological characteristics, Hai Phong, Van Uc estuary.
The biological analyses of 268 individuals of the Chinese gizzard shad (Clupanodon thrissa) collected by gill net in the area of Van Uc estuary from 09th August to 13th August, 2015 provided some important information: The total length of Clupanodon thrissa ranged from 68 mm to 215 mm, with 166.75 mm on average. Their weight ranged from 2.17 gr to 111 gr and mainly in 20 gr – 60 gr (60.07%). The equation of relationship between total length (TL) and weight (W) for the whole stock is W = 0.0000011 x L 3.4091 with R2= 0.9736. The fish caught stock included four age groups from 0+ to 3+ but primarily in the 2+ age group (40.30%) and 3+ age group (38.43%). The predominant food item groups were crustacean, phytoplankton which were found in almost all stomach and intestine of individuals examined. The second and the third degree of the stomach fullness made up significant percentages with 63.06% and 30.22%, respectively, while the first degree made up only a minor proportion (6.72%). Overall sexual ratio of females to males was 1.64 : 1. Sexual maturity of exploited fish individuals was essentially low, mainly at the stages II (66.42%) and only with 2.61% of the fishes caught being in stage IV of gonad maturity. Absolute fecundity was estimated with a range of 19,726 to 74,196 eggs and the relative fecundity ranged from 547 to 976 eggs per 1gr of fish weight, with 706 eggs per 1 gr of fish weight on average. These data show that the Clupanodon thrissa has been being overexploited, because exploiting fishes were mainly on young ones, which have not yet reached sexual maturity in the studied area.