Application of an Integrated Multitrophic Aquaculture System in Enhancing Production and Profitability in Small Scale Mariculture Enterprises in Kenya

Abstract

This study presents the first application of an integrated multi-trophic aquaculture (IMTA) system in pond culture in Kenya using local species. The overall goal was to identify and recruit new marine species for diversification of mariculture and increased income through adoption of environmentally friendly culture systems. The study was conducted in two trials: the first trial compared a monoculture of Indian white shrimp (Penaeus indicus) with an IMTA of Indian white shrimp as the fed component, and introduced sea cucumber (Holothuria scabra) and cockles (Anadara antiquata) as the extractive components. The trial was conducted in six brackish water ponds of 120 m2 and 1 m depth over a 135 days culture period. The monoculture treatment (T1) ponds were stocked with P. indicus juveniles at a density of 5 ind/m2. The IMTA treatment (T2) stocked H. scabra, P. Indicus and A. antiquata at 1.2 ind/m2, 5 ind/m2, and 3.5 ind/m2, respectively. Results showed that shrimps in monoculture treatment T1 attained a weight gain of 13.2± 0.75 g while in the IMTA treatment shrimps had a weight gain of 13.2 ± 0.57 g, sea cucumber gained 175.03 ± 27.84 g and cockles gained 44 ± 0.97 g. Survival was highest for P. indicus in IMTA at 80.1% and monoculture at 72.8% and lowest for H. scabra at 56.32%. The inorganic nutrient parameter of water significantly improved in IMTA system (p < 0.05) as compared to monoculture system. Of the five (5) phytoplankton classes recorded in water and plankton samples Bacillariophyceae dominated with 13.04 ± 20.62 cells/m 3 in IMTA and 6.57 ± 17.84 cells/m 3 in monoculture. The second trial used Nile tilapia (Oreochromis niloticus) acclimatized in marine water as the fed component in IMTA system with different species combinations. The study design had a monoculture of Nile tilapia as the control (C), a combination of O. niloticus and H. scabra as treatment 1 (T1), a combination of O. niloticus, H. scabra and oysters Sacostrea cucullata as T2, and T3 had a combination of O. niloticus and S. cucullata. Stocking in replicate ponds was at 2 ind./m2, 1.9 ind./m2 and 2.1 ind./m2 for Nile tilapia, sea cucumber and oysters respectively and in all treatments. Results showed that all organisms recorded weight gain over the 150 days study period; with O. niloticus recording a significantly higher (p < 0.05) average body weight (ABW) in T2. Treatments that had H. scabra as one of the extractive species recorded low survival rates i.e. 53 % in T1 and 45 % in T2. Production was highest in T2 where all three species were integrated. Net income was US$ 77.5 in IMTA compared to US$ (209) for the control while CBR was ≈1.0 for IMTA and ≈0.4 for the control. Collectively, the findings of these experimental studies demonstrated the potential of IMTA as a more profitable mariculture practice compared to monoculture; and is therefore recommended for adoption to promote production in earthen pond mariculture systems in coastal Kenya.