Domestic production of marine finfish is limited, in part, by the industry’s ability to produce sufficient quantities of high-quality juveniles, which can be partially attributed to inadequate nutrition during the larval stage. Existing larval microparticulate diets (i.e. microdiets) have several limitations that hamper their use as a replacement for cultured live feeds (Artemia and rotifers). Microdiets are prone to high rates of nutrient leaching when suspended in seawater which reduces the nutrient content of the ingested feed and potentially degrades water quality. In addition, these microdiets possess fast sinking rates, which can lead to low feed uptake and poor feed efficiencies for slow-swimming larvae. Ultimately, these factors may result in deficient nutrition for the larvae, which manifests as poor larval growth, low rates of survival, increased rates of malformations, and disease. Recent studies using liposomes containing water-soluble payloads have proved efficient at delivering essential nutrients to marine finfish. This is done by using liposomes to enrich live feeds, which are then consumed by early-stage larvae. Liposomes can also be incorporated into larger alginate-based carrier particles, hereafter referred to as liposome-containing complex particles (LCP), and can be ingested by larvae. These particles have the potential to deliver water-soluble compounds as well as a suite of macro- and micronutrients directly to fish larvae. This novel diet type has shown low rates of nutrient leaching in comparison to existing liquid and commercial type microdiets. In addition, LCP have been tested in preliminary growth studies with Inland silverside (Menidia beryllina) larvae and resulted in positive growth and high survival.
We hypothesize that liposome-containing complex particles will be able to efficiently deliver free amino acids and other key water-soluble nutrients to marine finfish larvae. The objectives of this research were to: 1) optimize buoyancy of LCP to increase rates of capture and ingestion by fish larvae; 2) evaluate payload efficiencies (i.e. encapsulation and retention efficiency) of core materials within liposomes and complex particles; 3) compare feed uptake rates, digestibility, and acceptability of LCP with those of commercial-type microdiets; and 4) evaluate success and viability of these diets for California yellowtail (Seriola dorsalis), a valuable commercial species. If successful, liposome-containing complex particles have the potential to transform the way marine finfish larvae are fed in commercial hatcheries. This diet type may increase larval growth, improve survival outcomes, and reduce malformation rates, thereby increasing overall production output from commercial hatcheries. Moreover, LCP may have broader uses beyond the delivery of water-soluble nutrients and act as an efficient delivery method for vaccines, antibiotics, and other bioactive compounds.