Exploring Isochrysis galbana Biomass Formats: Effects on Live Prey Oxidative Status and Lipid Profiles for Their Potential Use in Aquaculture Larval Nutrition

Feeding marine larvae commonly relies on live prey, which must be enriched with lipid emulsions and/or microalgae rich in long-chain polyunsaturated fatty acids (LC-PUFA) before being added to larval tanks. This enrichment enhances the nutritional value of live feed and supports larval health and growth. Microalgae are also used in aquaculture as a primary feed source for larvae and for maintaining water quality. However, in-house microalgal cultures are costly, prone to contamination, and require complex harvesting. Sourcing live microalgae from external specialized facilities is also expensive and complicated, as it involves transporting highly diluted biomass, creating a major bottleneck in hatcheries. Consequently, alternative formats of microalgal biomass, including fresh or dried forms, are gaining attention for their ease of use, nutritional stability, and antioxidant potential. To evaluate some of these concentrated biomass substitutes, different formats of Isochrysis galbana (spray-dried [ISD], fresh [IFRE], and frozen [IFRO]) were tested on the rotifer Brachionus plicatilis and Artemia. Prior to the assay, the total antioxidant capacity and lipid composition of the microalgal products were evaluated. Subsequently, live prey were fed the different I. galbana formats for 24 h, after which prey survival, lipid composition, and oxidative status were assessed. Our results showed that fresh/frozen I. galbana exhibited the highest in vitro antioxidant activity, particularly in the ethyl acetate fraction. However, rotifer survival was compromised when using the IFRE format. The spray-dried microalgae was the best format to enhance phospholipid retention in both zooplankton species, also increasing DHA/EPA (22:6n–3/20:5n–3) ratio and n–3 LC-PUFA content in rotifers. ISD also reduced lipid peroxidation in Artemia without negatively affecting the live prey culture. In conclusion, based on lipid composition and antioxidant potential, ISD was the most effective format for feeding rotifers and Artemia.