Shrimp-fish polyculture is considered to be a practice that can deal with environmental pollution and can limit shrimp diseases. In this way, it can potentially contribute to the sustainable development of the shrimp aquaculture industry. Firstly, the aim of this PhD study was to verify whether white shrimp (Litopenaeus vannamei) can be co-cultured with mullet (Mugil cephalus). Secondly, it was to investigate the impacts of shrimp-fish polyculture systems on water quality, animal production, and microbial community structures. Thirdly, the effect of shrimp-fish polyculture on shrimp immune parameters and on the prevalence of opportunistic pathogens, such as Vibrio, was studied.
Gray mullet (M. cephalus) is a local species, low in the trophic food chain. It is characterized by high tolerance to adverse conditions, rapid growth rate, high commercial demand and availability of fingerlings. Hence mullet is a promissory candidate for polyculture with shrimp. The results of a laboratory scale experiment indicate that polyculture of white shrimp and gray mullet is technically feasible. They also show that mullet can be co-cultured with shrimp at a fish stocking density equal to 10% of the shrimp biomass. This will improve water quality and total animal biomass production, creating a dynamic bacteria community structure while enhancing the nutrient conversion rate by the harvested organisms. In shrimp-fish polyculture, tilapia is considered a strong candidate and the first choice for shrimp polyculture. A comparative study indicated that shrimp-fish polyculture, in case of caged fish, is more effective when tilapia (Oreochromis niloticus) is used instead of mullet. However, under free-roaming conditions, shrimp-mullet polyculture is far more effective and outperforms the other tested systems.
At the moment, shrimp polyculture has not been common practice because it is mostly limited to extensive aquaculture systems. A combination of shrimp-fish polyculture and biofloc technology may have the potential to substitute low intensive shrimp polyculture systems. An indoor trial with a shrimp-fish polyculture system was conducted, where Litopenaeus vannamei was co-cultured with Mugil cephalus. The study indicated that the application of bioflocs in shrimp-fish polyculture systems has additive effects at the level of animal production and synergistic effects at the level of some water quality parameters. Additionally, the study also showed that the application of shrimp-fish polyculture systems does not contribute to the robustness of cultured shrimp. No difference in survival was observed upon challenge by Vibrio injection. However, the presence of mullet could reduce the prevalence of luminescent bacteria in shrimp culture tanks.
In conclusion, the PhD work indicated that shrimp-fish polyculture is a promissory strategy for sustainable development of shrimp aquaculture. It can result in increased animal production, enhanced nutrient conversion rate and hence improved water quality. It can also contribute to shrimp disease prevention. Taken together shrimp-fish polyculture can reduce environmental impact, contributing to a positive image of the aquaculture industry.