In marine finfish aquaculture, one of the greatest obstacles faced by producers, is the rearing of larvae and propagation of healthy juveniles. Providing adequate nutrition to early-stage marine finfish has proven difficult due to a number of technical challenges associated with the small artificial feeds (i.e microdiets) used to feed them. Microdiets tend to leach their water-soluble nutrients at very high rates when suspended in water, largely due to the high surface area-to-volume ratios of these small (100-1500 µm) particles. Leaching results in reduced payload delivery to target organisms as well as nutrient loading in the surrounding water. Nutritional deficiencies result in lower growth and survival and can have delayed effects on later life stages. In the present study, we evaluated novel coating technologies as a means of reducing the leaching of water-soluble nutrients from commercial microdiets to improve nutrient delivery to larval finfish.
Scanning electron microscope (SEM) images indicated that the protein coatings were effectively applied to the surface of commercial-type microdiets resulting in smooth surfaces with reduced porosity (Fig. 1). One of these specialized coatings was then applied to a modified open-formula microextruded marumerized (MEM) particle, designed for marine finfish larvae; hereafter, referred to as the “Protein Coated Microparticulate Diet” (PCMD). This diet was compared with similarly formulated uncoated microdiets and a commercial microdiet (Otohime) in benchtop, acceptability, and growth trials using larval Seriola dorsalis (California yellowtail). Protein coatings decreased the leaching of water-soluble nutrients while increasing particle stability of the PCMD’s when suspended in water. The results of the acceptability trial indicated that coated microdiets were consumed at equal rates when compared to non-coated microdiets. No significant differences in larval growth were observed at the end of the growth trial (Tukey’s HSD, p<0.05), however, larvae fed PCMD’s trended higher than those fed uncoated diets.
The reduced leaching of water-soluble nutrients by PCMD’s resulted in improved nutrient delivery and should reduce nutrient loading of larval culture systems. These coating technologies appear to be applicable to a wide range of commercial-type diets and may provide an opportunity to greatly improve the early life nutrition of marine finfish larvae.