Live feeds are essential in larval nutrition of many fish and crustacean species. As the consumers' demand for aquaculture products is growing rapidly, the demand for live feeds in larviculture is increasing as well. To satisfy the growing demand, research has taken steps to develop new innovative live feeds. Several studies focused on nematodes as a potential food source for larvae. Production methods, culture media, harvest, and enrichment procedures for nematodes presented in these studies are reviewed here. Many studies fed nematodes to different species of fish and crustaceans to test applicability in larval nutrition. The results of these feeding trials in terms of larval performance as well as ingestion and digestion of nematodes in the larvae's gut are reviewed here as well. In addition, a summary of advantages and disadvantages of nematodes as live food and an outlook on future challenges of production and application of nematodes in larviculture are also presented.
In summary, several different production methods including innovative culture media for nematodes have been developed. The species Panagrellus redivivus has been used in most of the reviewed studies. It reproduces extremely fast and can be cultivated by very simple means of production. Other species such as Turbatrix aceti and Caenorhabditis elegans have been tested in a few studies as well. However, a complete production cycle for mass production appropriate for use in aquaculture has not been developed yet for any of these species. Enrichment trials for amino acids revealed only a very limited potential to manipulate amino acid profiles in nematodes. In contrast, fatty acid composition turned out to be quite variable depending on the culture media used for nematode production. By adding oils containing large quantities of essential fatty acids to the culture media, these fatty acids could be enriched in nematodes and provided to larvae. This allows tailoring fatty acid composition according to the needs of the respective larvae. It could be shown that nematodes can be digested by fish larvae even though they possess a robust cuticle. Larval performance depends strongly on the respective species of fish to which the nematodes are fed. Nematodes seemed to work particularly well for crustacean larvae. In penaeid larvae, nematodes turned out to be a good live food that can compete with conventional feeding methods even though there is still room for improvements. For future use in larviculture, appropriate methods for mass production, harvest, and feeding need to be developed. Additionally, more data on optimized feeding levels for different fish and crustacean species will be required.