Growth and diet digestibility of cultured sablefish Anoplopoma fimbria : Implications for nutrient waste production and Integrated Multi-Trophic Aquaculture

Abstract

Sablefish (Anoplopoma fimbria) is a candidate species for the fed trophic level (FTL) in Integrated Multi-Trophic Aquaculture (IMTA) systems, given that its premium price can enable culture at smaller scales, potentially providing more farm area for co-cultured species. Sablefish production data were used to estimate nutrient waste loads over a production cycle to guide IMTA development. Growth and feed intake data from commercially cultured sablefish off the northwest coast of Vancouver Island (BC, Canada), were used to calculate thermal-unit growth coefficients (TGC) and feed conversion ratios (FCR). Apparent digestibility coefficients (ADC) for nutritional categories were determined by laboratory analysis, and a formula was developed to separate lipid and carbohydrate ADCs from bulk nitrogen free extract (NFE) data. Three linear growth stanzas were observed with breakpoints at 60g (SE 19.9) and 920g (SE 63.7): stanza 1 included fish <60g; stanza 2, fish between 60g and 920g; and, stanza 3, fish >920g. FCRs increased across stanzas 1–3, ranging from 1.20, 1.34, and 1.62, respectively. TGCs decreased across stanzas 1–3, ranging from 3.12, 2.39, and 1.47, respectively. ADCs for protein, lipid, carbohydrates and energy were 93.0%, 97.4%, 70.9% and 88.8%, respectively. A TGC model simulated growth over a 19month production cycle. Growth, FCR and ADC data supplied inputs for nutritional mass balance estimates of a monthly elemental carbon and nitrogen load per fish. Model estimates suggest that peak monthly nutrient loading does not occur during maximum temperatures in August, but during November of year one and September of year two. The predicted peak nutrient loading in year two was 1.7 times greater than the peak loading in year one, less than half the annual loading difference reported for cultured Atlantic salmon (Salmo salar). The slower relative growth rate of large sablefish reduces the discrepancies between annual peak loading periods, enabling better matches of co-cultured species biomass with nutrient supply. These findings provide information useful for deploying sablefish as a FTL for IMTA. Statement of relevanceThis research enhances data on sablefish production and nutrition. It is the first study to document three linear growth stanzas and reduced growth rate of sablefish as they approach 1 kg. We assess sablefish as a candidate species for the upper trophic level in open-water Integrated Multi-Trophic Aquaculture (IMTA) systems. Unique quantitative and qualitative nutritional data is presented to guide producers.