Identification of two hatch date-dependent cohorts and variation in early growth rate of mud carp (Cirrhinus molitorella) in the Pearl River Delta, China

Cirrhinus molitorella is one of the most important commercial fish species in the Pearl River, but there are few published studies on the early growth of this species. In the present study, seasonal recruitment patterns, temporal variations in early growth rates and environmental variables were analysed. In all, 1512 individuals were collected during monthly sampling from July 2015 to January 2016, ranging from 30.8- to 84.9-mm standard length (SL). A subsample of 276 juveniles was aged from 68 to 193 days, with hatch dates between 2 February and 19 September, by determining daily increments in otoliths. Monthly abundance data and SL frequency distributions showed that there were two major temporal cohorts of juvenile recruitment, which hatched primarily in April and July. Average growth rate, estimated by the linear relationship between age and SL, was greater for the April cohort (0.49mmday–1) than the July cohort (0.37mmday–1). Mean increment widths from the 23rd increment onwards were significantly greater for the April than July cohort (P<0.05). The slower growth observed in the July cohort was probably due to poorer food availability caused by high river discharge volumes. These results are important for predicting recruitment dynamics and managing the C. molitorella fishery.

Comparison of nutrient composition in wild caught and cultured Cirrhinus molitorella (Valenciennes, 1844)

Proximate body composition and amino acid profile of flesh of wild Cirrhinus molitorella (Valenciennes, 1844) from a reservoir and a river was compared with that of C. molitorella cultured in an aquaculture pond. The results showed the fat content to be highest in C. molitorella caught from reservoir followed by samples from river and lowest in pond cultured fishes. Protein content exhibited the opposite trend. Flesh of C. molitorella from river had optimum protein quality while flesh of fishes from reservoir had the best taste. Flesh of C. molitorella was found to be nutritionally rich and well balanced and its high glutamic acid as well as lysine content made it a superior forage fish for Siniperca chuatsi. Overall, C. molitorella flesh had a more balanced nutritional composition, but lower nutritional value than that of seven other reference fish species.