Fecundity and Gonadal Development of Copper Mahseer, Neolissochilus Hexagonolepis (McClelland, 1839) from Tamor river, Nepal

Abstract

The present work was intended to assess the fecundity and gonadal development of Neolissochilus hexagonolepis from Tamor River, Nepal. The study was conducted for the duration of two years, from December 2014 to November 2016. Monthly samples of N. hexagonolepis were procured from the river. Altogether one hundred ninety eight samples were examined. The length-weight relationship (LWR) was found to be following the model of Le Cren (1951). The value of the regression coefficient (b) for all the LWR was close to 3, which indicated that the fish showed an isometric growth pattern. The general well being of the fish from the river was found to be satisfactory. The assessment of fecundity unveiled N. hexagonolepis as a low fecund fish. The number of eggs in the ovaries of N. hexagonolepis increased proportionately with increasing length, body weight and gonad weight of the fish. The enumeration of gonado-somatic index (GSI) showed the species as an annual breeder with peak spawning activity from July to August. The egg size estimation revealed the species as a multiple spawner. Male individuals dominated the smaller size classes and female individuals dominated the larger size classes. The testes and ovaries were observed at six stages of maturation viz. Immature, maturing virgin, ripening, mature, spawning and spent. The developing oocytes within the ovigerous lamellae of the ovaries were observed at the chromatin-nucleolus stage, early and late peri-nucleolus stages, early and late yolk vesicle stages and early and late yolk stages. The species showed an extended breeding period from May to November. Male and female individuals attained the first sexual maturity at size 25.5 cm and 32.9 cm, respectively. Environmental variables played an essential role in governing the reproductive biology of the fish. Temperature contributed positively to the development of the fish’s gonads during its breeding season.