Characterizing trophic interactions of a catfish dominated tropical reservoir ecosystem to assess the effects of management practices.

Abstract

The trophic interactions and energy flows of a tropical reservoir was carried out to assess the effect of stocking carps as a management strategy on the food web of the reservoir ecosystem using mass balance modelling. The model structured around 13 ecological groups which included the most dominant catfishes Mystus spp. The trophic level of the reservoir varied between 3.63 and 1.0, with the largest values corresponding to aquatic birds, and the carnivorous fishes (other catfishes, Mystus spp and snake-heads) acting as top predators upon system resources at lower trophic levels. The ecotrophic efficiency was highest for the planktivorous fishes (major carps, minor carps and minnows) whereas low values were recorded for the most dominant fish group, the catfishes. The mixed trophic impact routine shows that the, Mystus spp. have a strong negative impact on minor carps and minnows but the other catfishes (Wallago attu and Ompok bimaculatus) have a slight positive impact on the major carps (the stocked fishes). The snakeheads (Channa marulius and Channa punctatus) exert negative impact on their preferred prey, major carps. The reservoir has a detritus based food chain, where almost all the biomass is concentrated in the first two trophic levels (the producers level and the herbivore/detritivore level), with rather low transfer efficiencies. The primary production/biomass ratio was 80.33. Finns Cycling Index was estimated at 1.99 % of the total system throughput. All the attributes of ecosystem maturity and stability explicitly indicate that the ecosystem is in developmental phase