Abstract
Aquaculture threatens natural resources by fishing down the sea to supply fishmeal. Alternative protein sources in aquafeeds can provide a solution, particularly those that are waste from other operations and thereby reduce feed production costs. Toward this goal, we examined the waste biomass of marine periphyton from biofilters of an integrated multi-trophic aquaculture (IMTA) system as a replacement for fishmeal in diets of gilthead seabream (Sparus aurata). Four isoproteic (41%) and isolipidic (16.7%) aquafeeds were formulated with increased content of periphyton and a corresponding decrease in fishmeal from 20 to 15, 10, or 0%. The growth and biochemical content of seabream fingerlings (initial body weight 10 g) were examined over 132 days. Replacing 50% of fishmeal by waste periphyton improved feed conversion ratio (1.2 vs. 1.35 in the control diet) without harming fish growth. The complete replacement of fishmeal with periphyton resulted in 15% slower growth but significantly higher protein content in the fish flesh (59 vs. 52% in the control diet). Halving fishmeal content reduced feed cost by US$ 0.13 kg−1 feed and saved 30% in the cost of conversion of feed to fish biomass (US$ 0.58 kg−1 produced fish vs. $0.83 in the control diet). Finally, the total replacement of fishmeal by waste periphyton in the diet reduced the fish in—fish out ratio to below 1 (0.5–0.9) as compared to 1.36 in the control diet. Replacing fishmeal with on-farm produced periphyton minimizes aquaculture footprint through the removal of excess nutrients in effluents and the use of waste biomass to reduce the ‘fish in’ content in aquafeeds and fish production costs. The present study demonstrates the great practical potential of this dual use of marine periphyton in enhancing the circular economy concept in sustainable fish production.
Highlights
IntroductionAlternative protein sources in aquafeeds can provide a solution, those that are waste from other operations and thereby reduce feed production costs
Aquaculture threatens natural resources by fishing down the sea to supply fishmeal
The cost of fishmeal has been reduced in recent years to around 1500 USD per tonne, with the limitation in natural resources for this ingredient due to o verfishing[2,3] it is expected to increase in the future
Summary
Alternative protein sources in aquafeeds can provide a solution, those that are waste from other operations and thereby reduce feed production costs Toward this goal, we examined the waste biomass of marine periphyton from biofilters of an integrated multi-trophic aquaculture (IMTA) system as a replacement for fishmeal in diets of gilthead seabream (Sparus aurata). Replacing fishmeal with on-farm produced periphyton minimizes aquaculture footprint through the removal of excess nutrients in effluents and the use of waste biomass to reduce the ‘fish in’ content in aquafeeds and fish production costs. The use of such alternatives in diet may result in poorer growth performance of fish, as reported in sea b ream[7,8,9] and Atlantic s almon[10,11] This is probably due to the presence of anti-nutritional factors in some of these raw materials which harm nutrient digestion and absorption[12,13]. As in other plant/algal biofilters, frequent harvesting of the periphytic biomass is required to keep both biomass production and nutrient removal rapid[22,30], while the protein-rich harvested biomass is considered waste unless used for other purposes
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