Integrated Multitrophic Aquaculture of Molobicus Tilapia, White Shrimp (Penaeus vannamei) and Seaweed (Gracilaria sp.) in Tanks

Abstract

Integrated Multitrophic Aquaculture System (IMTA) is a polyculture system which grows organisms from different level of the food chain in one environment where wastes from one species serves as the source of food or nutrients for other organisms. In this study, the IMTA system was tried using Molobicus tilapia (main cultured and fed species), white shrimp (unfed species) and Gracilaria sp. (as biofilter species). The study aimed to determine the growth and survival of Molobicus Tilapia at different stocking densities (20, 40, and 60 fish per tank) co-cultured with P. vannamei and seaweed (Gracilaria heteroclada) in round plastic tanks and to monitor the different water parameter in terms of dissolved oxygen, pH, temperature, ammonia, nitrite, and nitrate. Results showed no significant differences in weight gain, length gain, specific growth rates (weight and length), and survival rates of tilapia at the different stocking densities tested. However, in terms of growth rates and survivorship of the white shrimps, there were significant differences among treatments. Treatment III (highest stocking density of tilapia) showed fastest growth in terms of length and weight of the white shrimp, but also resulted to lowest survival rates as compared to Treatments I and II (lower stocking densities of tilapia). Faster growth of white shrimps was observed in Treatment III because of the higher feed ration given to the tilapia as well as higher amount of wastes in the form of uneaten food and fecal matter. However, the higher stocking densities of tilapia in Treatment III also resulted to a density-dependent effect on survival rates of the white shrimps. During the course of the 75-day culture period, there was a decreasing trend in the biomass of the seaweeds (Gracilaria sp.), which coincided with increasing trend of nitrogenous compounds such as ammonia, nitrite, and nitrate, which was more pronounced in higher stocking densities of tilapia in Treatment III. High ammonia levels are well known to negatively affect growth and survival rates of aquatic organisms.