HABITAT ECOLOGY AND REPRODUCTIVE BIOLOGY OF GAGORA CATFISH (ARIUS GAGORA)

Abstract

In the present study, habitat ecology and the aspects of reproductive biology of Arius gagora were assessed through histology of gonads in Monu River from July 2013 to June 2014. Twenty species of catfish belonging 8 families were identified. The yearly mean Shannon-Weaver diversity index, Margalef richness index, Pielou’s evenness index and Simpson dominance index were found to be 1.86, 1.48, 0.95 and 0.83, respectively. The diversity indices showed significant differences except Pielou’s evenness index in catfish assemblage structure. At the similarity percentage (SIMPER) 85.65, three groups were attained while summer showed separate clustering from other groups. The Nonmetric

Multidimensional Scaling (n-MDS) showed 60% similarity in all seasons based on Bray-Curtis similarity matrix. The CCA (Canonical correspondence analysis) ordination indicated that TDS and transparency were the two most important environmental parameters shaping the catfish assemblage structure in river Monu. Ovarian development of A. gagora was assessed macroscopically and microscopically. The fecundity found to be ranged from 43333.12±829.83 to 53948.81±1743.28 in April to August. The relationship of fecundity with ovary weight, ovary length, total length and total weight found to be positively correlated. Length weight is found to be strongly correlated with r 2 value of 0.986 and 0.982 for male and female respectively. Results of the study revealed female dominance of the species over male with a ratio of 1:1.82 (female: male) and showed earlier maturation than male too. Three gonadal maturity stages namely immature (early primary oocyte, late primary oocyte and yolk vesicle oocyte), maturing (early and late yolk globule) and matured for female and immature (spermatogonia, primary and secondary spermatocytes), maturing (spermatid) and matured (spermatozoa) were identified for male fishes. Monthly study of gonado somatic index (GSI) revealed that the breeding season for this fish species may be extended from July to August with a single peak spawning month in August. Presence of mature oocytes in ovary samples during June-August indicated mature phase of oocytes ready to spawn. The histological study of ovary over the year indicated that female gametes of A. gagora are asynchronous in nature.