The unicellular green alga Chlorogonium capillatum as a live food promotes the growth and survival of Artemia larvae

Freshly hatched fish and small crustaceans feed on small living organisms such as bacteria and living protozoa, collectively referred to as infusoria. The larval stage of these animals is crucial in aquaculture fisheries; however, the supply of commercial infusoria is challenging as naturally occurring infusoria may contain organisms that are harmful to larvae. Brine shrimp (Artemia franciscana) require proper nutrition immediately after hatching otherwise they die within a few days. The purpose of this study was to search for protists suitable for use as live bait for the larvae of these animals. In this study, Tetrahymena pyriformis (Ciliophora, Alveolata), Euglena gracilis (Excavata), and Chlorogonium capillatum and Chlorella variabilis (Archaeplastida) were fed to the freshly hatched brine shrimp for 10 days. The most suitable protist for the larvae was identified based on the survival and growth rate of the brine shrimp. Microscopic observation of the inside of the brine shrimp's digestive tract two days after hatching was used to confirm that protists were sufficiently small to be predated on by the brine shrimp. This study found that C. capillatum was the best in terms of both survival rate and growth rate and was suitable as a diet for brine shrimp larvae. The results indicate that of the five protists studied, C. capillatum is the most suitable food for brine shrimp larvae. In contrast, the survival rate of brine shrimp was significantly reduced when E. gracilis was given, suggesting that E. gracilis contains substances that are harmful to brine shrimp. This highlights a need for research into the safety of Euglena, which has been highly regarded in recent years as an excellent healthy food with high nutritional value.