Reproductive biology of Gangetic leaffish Nandus nandus (Hamilton 1822) from Borsola beel, Jorhat, Assam

Abstract

The present study has been carried out from the Borsola a floodplain wetlands of Jorhat district, Assam from January, 2017 to June, 2019. The Gangetic leaf fish, Nandus nandus (family: Nandidae) is an important edible species found in the slow moving and stagnant water bodies of Brahmaputra basin. Out of 187 fish specimens examined, 91 were males and 96 females. Usually the females are larger in size and have shorter dorsal and anal fin, whereas the males are brighter in colour. The sex ratio (M:F) ranged from 1:0.7 to 1:1.33. The gonado-somatic ratio value for male was ranged 0.53±0.13 (December) to 2.97±1.19 (July) and for female from 0.75±0.38 (December) to 16.37±4.48 (July). The GSR increases gradually from February to August and being peak in July for both males and females, but abruptly declines in October onwards and again found to be increased in February. The maximum GSR value for both the males (2.81±1.39) and females (15.53±3.57) was observed in ripe (gravid) stage whereas the minimum (0.38±0.26) for males and female (0.42±0.22) was recorded in spent individuals. The average ova diameter was ranged from 0.52±0.02 mm (January) to 0.68±0.04 mm (July). The lowest (0.5 mm) ova diameter was observed in immature stage and that of highest (0.71 mm) was in ripe stage. The size of the ova was gradually increase from January onwards and being peak in July. The absolute fecundity was found to be highly fluctuating and varies between 4428.4 and 38332.3. The relative fecundity was ranged from 130.98 to 1081.61. The maximum absolute fecundity (25212.89±5536.47) was found in the length group of 12.6-15.5 cm while the minimum (7521.90±823.44) in the length group of 6.5-9.5 cm. In case of relative fecundity, it varied from 544.23 (±420.56) to 649.30 (±491.26) in the size group of 6.5-9.5 and 9.6-12.5 cm respectively. It reveals that species has high and moderate fecund and observed spawning period from April onwards upto August and spawned once in a year with peak being in June/July.