Integrated tank cultivation of salmonids and Gracilaria chilensis (Gracilariales, Rhodophyta)

Abstract

Oncorhynchus kisutch, O. mykiss and Gracilaria chilensis cultivation in intensive tank systems is feasible. The environmental benefits associated with the development of integrated tank cultivation were established by analyzing previously published and unpublished data on fish production and food conversion efficiency, particle discharges in fish effluents, as well as biomass production, nutrient uptake efficiency data of Gracilaria, with special emphasis on ammonium. The results indicate that fish production can reach 30 kg m⁻³ during a production cycle, and food conversion can be maintained stably at 1.4 g food g fish⁻¹ production during the entire cultivation period. The solid particle discharges can be as high as 2.1 g (dry) kg fish⁻¹ day⁻¹ during the spring and summer, when salmon cultivation reaches its highest densities. The nutrient that increases most in fish effluents is ammonium, reaching concentrations as high as 500 µg 1⁻¹, also in spring and summer. Gracilaria production can reach production rates as high as 48.9 kg m⁻² year⁻¹ and is able to remove 50% of the dissolved ammonium in winter, increasing to 90–95% in spring. These results are integrated into an income-analysis model, adding the extra income for Gracilaria harvesting and internalizing the environmental benefits for a 100-ton salmon production unit, which indicates that an additional total revenue of over US$ 60 000, representing around 10% of the total income, is possible.