Trophic state index ( TSI ) and carrying capacity estimation of aquaculture development; the application of total phosphorus budget

Abstract

The aquaculture industry is crucial for sustainability and food security. Nevertheless, it is also one of the significant causes of water quality degradation, reducing water bodies' carrying capacity. One of the degradation factors is the improper discharge of phosphorus. This study aimed to evaluate the trophic state index (TSI) and carrying capacity for tilapia aquaculture development at the Temengor Reservoir, Malaysia, based on the Dillon–Rigler phosphorus budget model. The data permit the evaluation of the limit for fish production capacities that could retain acceptable water quality conditions. This study was carried out monthly from January 2014 to May 2015, focusing on cage sites within the Aquaculture Industrial Zone (AIZ). A total of 15 sampling points were established within a 5-km radius of the fish cages at 1 km horizontal intervals. The TSI values based on three indicators, total phosphorous, Secchi depth and chlorophyll-a, showed a significant difference (p < 0.05) among sampling points. Areas in the vicinity of the fish cages (<3 km) were at a eutrophic state. However, the current aquaculture production at 9.13 × 103 tonnes per year, which comprises three fish cage modules, has not yet reached the optimum capacity of 325.23 × 103 tonnes per year. Although the lake could accommodate another 105 fish cages, the eutrophic state near the cages signalled water quality deterioration. As there is a plan to increase the number of cages, it is hoped that these findings will be taken into serious consideration in the implementation of any aquaculture expansion in this man-made lake.