Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

• Published in: Aquacultural engineering Vol. 39; no. 2; pp. 113 - 121
• Main Authors: Gilles, Sylvain, Lacroix, Gérard, Corbin, Daniel, Bâ, Ngansoumana, Luna, Carla Ibañez, Nandjui, Jacob, Ouattara, Allassane, Ouédraogo, Ousséni, Lazzaro, Xavier
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-01-2008; [Amsterdam]: Elsevier Science; Elsevier
• Subjects: Agnatha. Pisces; Algae; ammonia; Animal aquaculture; Animal productions; aquaculture systems; Biodiversity and Ecology; Biological and medical sciences; carbon dioxide; Chlorella; CO 2-limitation; detoxification (processing); detritivores; dissolved organic carbon; Environmental Sciences; fish culture; fish farms; Fish-algae mutualism; Fundamental and applied biological sciences. Psychology; General aspects; intensive farming; Marine; marine sediments; mineralization; nitrates; nitrification; nitrogen; phosphates; phosphorus; Photosynthetic recycling aquaculture system; phytoplankton; Phytoplankton mass production; population density; recirculating aquaculture systems; Sarotherodon; Sarotherodon melanotheron heudelotii; Tilapia; tilapia (common name); tropics; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Senegal; Phytoplankton mass production; Chlorella; CO 2-limitation; Tilapia; Photosynthetic recycling aquaculture system; Sarotherodon melanotheron heudelotii; Fish-algae mutualism; Mass production; Algae; Carbon dioxide; Chlorophyceae; Mutualism; Environmental engineering; Photosynthetic system; Vertebrata; Chlorophyta; Recirculating flow; Pisces; Phytoplankton; CO2-limitation; Recycling; Euryhalinity; Aquaculture; tilapia; phytoplankton mass production; photosynthetic recycling aquaculture system; fish-algae mutualism
• ISSN: 0144-8609; 1873-5614
• DOI: 10.1016/j.aquaeng.2008.09.001

The West-African euryhaline tilapia,
Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems,
S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using
S. m. heudelotii and
Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of
S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of
Chlorella initial density.
Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with
Chlorella initial density.
S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by
Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability.
Chlorella differential responses with fed vs. unfed
Sarotherodon suggest that CO
2 supplied by heterotrophic
S. m. heudelotii respiration played a key role. Observed
Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO
2, nitrate and phosphate, under artificial lighting.
Our results suggest the existence of a
Sarotherodon-Chlorella mutualism in our systems, where
S. m. heudelotii provide CO
2, the major limiting factor of
Chlorella growth, whereas
Chlorella oxygenate and detoxify the water media from ammonia, promoting
S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.