Abstract
Polychaetes can be successfully employed to recover essential fatty acids (EFA) from wasted uneaten aquafeeds present in aquaculture effluents. The optimization of the timeframe required to produce premium ragworms (Hediste diversicolor) biomass rich in EFA is paramount to make available to the aquafeeds industry another alternative ingredient to fish meal and fish oil. The present study aimed to evaluate the potential enrichment of ragworms fatty acid (FA) profile when fed a commercial aquafeed during 10, 20, and 40 days (D10, D20, and D40) under different combinations of water temperature (20 and 25°C) and salinity (15, 20, and 25). Total FA incremented progressively overtime, with D40 polychaetes exhibiting average values ranging between 70 and 90 μg mg–1 DW. The average values of n-6 FA ranged between 13 and 17 μg mg–1 DW, while that of n-3 FA varied between 17 and 19 μg mg–1 DW at D40. No significant differences were found in the FA profile of H. diversicolor cultured under different combinations of temperature and salinity. The FA profile of cultured polychaetes exhibited between 28 and 31% dissimilarity from that of wild conspecifics and displayed a higher content of two essential n-3 FA: eicosapentaenoic (20:5 n-3, EPA) and docosahexaenoic acids (22:6 n-3, DHA) (values ranging between 9.6–11.2% and 4.3–5.0% of total FA, respectively). A higher similarity in FA profile was recorded between D40 polychaetes and aquafeed than with initially stocked or wild specimens. Palmitic (16:0), oleic (18:1 n-9), linoleic (18:2 n-6), eicosadienoic (20:2 n-6), EPA (20:5 n-3), and DHA (22:6 n-3) were the FA whose concentration exhibited the highest increment. Evidence of de novo FA biosynthesis was observed through the formation of some FA that were neither present in the initially stocked biomass, nor in the aquafeed supplied, such as 5,11-eicosadienoate (Δ5,1120:2), 7,13,16-docosatrienoate (Δ7,13,1622:3), dihomo-gamma-linolenic (20:3 n-6), eicosatrienoic (20:3 n-3) and eicosatetraenoic (20:4 n-3) acids. A plateau of total FA, n-6, and n-3 FA was not reached over the study period. Overall, the present study highlights the potential of H. diversicolor as an extractive species for integrated multi-trophic aquaculture (IMTA) applications.
Highlights
World aquaculture production reached an all-time record of 114.5 million tons in live weight in 2018 (USD 263.6 billion) (FAO, 2020)
In order to shed some light over the above-mentioned questions, the present study aimed to evaluate the evolution of the FA profile of H. diversicolor fed a commercial aquafeed during 10, 20, and 40 days (D10, D20 and D40) under different combinations of water temperature (20 and 25−C) and salinity (15, 20, and 25)
No significant differences were found for Feeding Rate (FR), specific growth rate (SGR), and Daily Growth Rate (DGR) exhibited by polychaetes at D10, D20, and D40 (p > 0.05; Supplementary Table 3)
Summary
World aquaculture production reached an all-time record of 114.5 million tons in live weight in 2018 (USD 263.6 billion) (FAO, 2020). This figure includes the production of 54.2 million tons of fish (USD 139.7 billion) and 9.4 million tons of crustaceans (USD 69.3 billion), with 13 and 61% of these productions resulting from saltwater aquaculture (which includes marine and brackish water species), respectively (FAO, 2020). The majority of farmed species of both groups are produced using commercial aquafeeds (∼ 57 million tons in 2018) (FAO, 2020). Formulated aquafeeds have to both satisfy the nutritional needs of cultured species and safeguard that at the end of a productive cycle farmed species display an optimal biochemical profile for human nutrition
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