Growth and mortality of two small fishes, Toxabramis swinhonis Günther, 1873 and Hyporhamphus intermedius (Cantor, 1842), in a Yangtze shallow lake (China) assessed by length frequency analysis

Abstract

This study examined the growth and mortality of two widespread small fish species, Toxabramis swinhonis (Cyprinidae) and Hyporhamphus intermedius (Hemiramphidae), from a shallow lake (Niushan Lake, China) along the Yangtze River, by analyzing monthly length frequency data (July 2005 to June 2006) with the FAO-ICLARM stock assessment tool (FiSAT). Estimated von Bertalanffy growth equation parameters were: L (asymptotic length)=145mm TL, and K (growth coefficient)=0.66year(-1) for T.swinhonis; L=189mm TL, and K=0.68year(-1) for H.intermedius. The instantaneous rates of natural mortality (M) calculated for T.swinhonis and H.intermedius were 1.35 and 1.28year(-1), respectively. The length-converted catch curve method gave the total annual instantaneous mortality rate (Z) of 2.92year(-1) for T.swinhonis and 1.53year(-1) for H.intermedius. Recruitment patterns of both species were continuous, displaying a single major peak event per year. Despite not being of direct fishing interest, T.swinhonis, with high abundance and productivity as indicated by a high Z-value, can be an important species in fisheries management as an excellent food source for aquatic organisms, especially for larger fishes of economic value. These results represent the first information on population characteristics of T.swinhonis and H.intermedius, and constitute a comparison base for future growth studies in other lake environments.