Cod Larviculture Using High‐density Rotifer Production with Different Enrichments

Abstract

High‐density (HD) rotifer culture systems have been recently commercialized, but are not commonly used by the aquaculture industry. The aim of this study was to determine if HD systems could be used in cod hatcheries. An enrichment strategy using the commercial products, ArteMac and Protein Selco Plus (Com), was compared with the manufacturer's suggested enrichment, using Pavlova‐DHA (Pav). The Pav enrichment increased the eicosapentaenoic acid (EPA) levels in rotifers, but reduced the docosahexaenoic acid (DHA) and 22:5n‐6 (n‐6DPA, docosapentaenoic acid) levels. Larvae EPA levels in both polar and neutral lipids were relatively stable in the larvae fed with Com‐rotifers; while they were higher in early stages, they were progressively reduced through ontogeny in the Pav‐rotifers fed‐larvae. DHA levels in polar lipids decreased in larvae, particularly when fed with HD‐Pav rotifers. In all larvae, arachidonic acid (ARA) levels increased in the polar and neutral lipids, regardless of treatments. In both lipid fractions, the levels of ARA were quite stable in time, but still higher in larvae fed with Com‐rotifers. Bacterial load was lower in larvae fed with Pav‐rotifers. Denaturing gradient gel electrophoresis (DGGE) bacterial profiles of larvae and rotifers were all similar. This study shows the potential of using HD systems to produce rotifers, but highlights the necessity of adjusting the nutritional composition of rotifers prior to being fed to larvae.

An Early Larval Feeding Protocol and Hypersaline Acclimation of Larval Spotted Seatrout

“…Many vital nutrients are required for the growth, proper development, and survival of marine fish. Several studies with marine finfish suggest that the essential fatty acids (EFAs) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are highly important during early development (Palmtag et al 2006;Seychelles et al 2009;Kotani et al 2010;Maehre et al 2013;Ma and Qin 2014;Hache et al 2017). Most marine fish larvae are unable to convert short-chain fatty acids into long-chain fatty acids such as DHA and EPA in sufficient quantities to meet the physiological demands of rapid growth taking place at this stage (Palmtag et al 2006;Ma and Qin 2014).…”

“…In the case of rotifers that are fed to early stage larvae, DHA and EPA are supplied by enriching the rotifers with either microalgae or commercially prepared enrichment products like those that were evaluated in the present study. Enrichment is necessary to increase the fatty acid profiles of rotifers, as they are naturally low in DHA and EPA (Palmtag et al 2006;Hache and Plante 2011;Hache et al 2017). Achieving adequate levels of DHA and EPA in rotifers that are fed to larval fish is particularly important due to larvae often having higher requirements for these EFAs than adult fish (Maehre et al 2013).…”

“…Hendon and Rakocinski (2016) found that early growth patterns are a critical predictor of survival rates of hatchery-reared Spotted Seatrout. To promote optimum larval growth and survival, extrinsic feeds should contain appropriate levels of nutrients, including essential fatty acids such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) for marine species (Seychelles et al 2009;Ma and Qin 2014;Hache et al 2017). These nutrients are typically supplemented in the diets of fish during the early larval stage by enriching live feeds, such as rotifers, before feeding them to the larvae.…”