An integrated fish–plankton aquaculture system in brackish water

Abstract

Integrated Multi-Trophic Aquaculture takes advantage of the mutualism between some detritivorous fish and phytoplankton. The fish recycle nutrients by consuming live (and dead) algae and provide the inorganic carbon to fuel the growth of live algae. In the meanwhile, algae purify the water and generate the oxygen required by fishes. Such mechanism stabilizes the functioning of an artificially recycling ecosystem, as exemplified by combining the euryhaline tilapia Sarotherodon melanotheron heudelotii and the unicellular alga Chlorella sp. Feed addition in this ecosystem results in faster fish growth but also in an increase in phytoplankton biomass, which must be limited. In the prototype described here, the algal population control is exerted by herbivorous zooplankton growing in a separate pond connected in parallel to the fish-algae ecosystem. The zooplankton production is then consumed by tilapia, particularly by the fry and juveniles, when water is returned to the main circuit. Chlorella sp. and Brachionus plicatilis are two planktonic species that have spontaneously colonized the brackish water of the prototype, which was set-up in Senegal along the Atlantic Ocean shoreline. In our system, water was entirely recycled and only evaporation was compensated (1.5% volume/day). Sediment, which accumulated in the zooplankton pond, was the only trophic cul-de-sac. The system was temporarily destabilized following an accidental rotifer invasion in the main circuit. This caused Chlorella disappearance and replacement by opportunist algae, not consumed by Brachionus. Following the entire consumption of the Brachionus population by tilapias, Chlorella predominated again. Our artificial ecosystem combining S. m. heudelotii, Chlorella and B. plicatilis thus appeared to be resilient. This farming system was operated over one year with a fish productivity of 1.85 kg/m 2 per year during the cold season

An integrated closed system for fish-plankton aquaculture in Amazonian fresh water

“…(Gilles et al, 2013). The N retention of the Channel Catfish was 36.3%, with a 36% protein floating catfish food, and a FCR of 1.24.…”

“…It operated as a closed recirculating system (Figure 1), housed in a greenhouse with mosquito net protection, and employing two connected lined wooden sewage tanks (T1 and T2 -extensive or sewage part) with a cage (intensive part) containing P. punctifer juveniles suspended in the first. Two lined wooden zooplankton tanks (Z) were connected in parallel with the main circuit (T1 and T2) following (Gilles et al, 2013), in order to eventually control the phytoplankton biomass. Each sewage tank had a useable volume of 3 m 3 of water (4 m long × 1.5 m wide × 0.5 m deep) and the cage a useable volume of 0.24 m 3 (1.25 m long × 0.6 m wide × 0.32 m deep).…”

“…Given that 63.7% N consumed by P. punctifer was excreted and then consumed by omnivorous fish in the sewage part (mainly cichlids, whose weight gain increased significantly), with a 47% N retention, it is possible to check if the N excreted by sewage fish corresponds to N dissolved plus N included in phytoplankton (last equation). Using the same protocol for measuring the OD as was employed in Senegal (Gilles et al, 2013), with the same or closely related alga species (Chlorella), it is possible to establish a relationship between OD and N amount corresponding to the phytoplankton density.…”

“…An alternative system was developed in Senegal (Gilles et al, 2013), using brackish water for rearing the West African detritivorous and euryhaline tilapia, Sarotherodon melanotheron heudelotii Dumeril, 1858 (Pauly, 1976;Trewavas, 1983;Falk et al, 2000). The fish were fed commercially manufactured pellets in the intensive part of the system, but were not supplied with food in the sewage ponds, obliging them to consume waste material (i.e.…”

Egg production in the euryhaline tilapia,Sarotherodon melanotheron heudelotii, experimentally maintained in fresh, sea and hypersaline waters

“…It is also a good candidate for aquaculture in African lagoons and was the subject of several studies on an integrated fish-plankton aquaculture system in brackish water (Gilles et al 2008(Gilles et al , 2013.…”