Fish community structure and trophic status-a measure of ecological degradation: A case study from Powai Lake Mumbai.

Abstract

Powai lake, a monomictic shallow lake, presenting some characteristics typical of a progressive trophic state specifically the permanent turbid water, the recurrent occurrence of cyanobacterial blooms which occasionally leads to large fish kills and the reduction in biodiversity. The study was carried out to understand the ecological degradation of Powai lake by using the abiotic and biotic factors. Twenty-four fish species were recorded and the fish yield was found to be 98 kg ha yr where -1 -1 here the actual potential lies about 363 kg ha-1 yr-1. The diet composition of 10 of the most abundant fishes in the lake revealed that, there were about 13 major food items from the gut contents, includes phytoplankton green algae, phytoplankton blue-green algae, diatoms, cladocerans, copepods, benthic algae, benthic weeds, macrophytes, detritus, fish eggs and larvae, shrimps, fish scales and insects parts. The Food Richness index (N) varied from 12 (Heteropneustes fossilis) to 29 (Oreochromis mossambicus), Diet Breadth (D) from 0.12 (Heteropneustes fossilis) to 0.77 (Oreochromis mossambicus) and the Gut repletion index (GRI) as 100% for all the species. Most of the fish species in the lake were either planktivores or detritivores with high feeding avidity and trophic adaptability, hence are capable of altering diet according to availability. The estimated trophic level indicates that almost all the fishes in the lake depend on primary producers or consumers as their diet. The dominance of omnivores and planktivores and the submissive occurrence of carnivores in the lake indicates the rampant ecological degradation of the lake.