Nutrient stimulation of epidermal growth in developing Artemia

The ability of dietary components to support growth of the epidermal cells was examined in fourth-instar brine shrimp larvae. Larvae fed Encapsulon particles increased in thoracic length by 12% and segment 1 width by 9%. Addition of Artemate, a polyunsaturated fatty acid-rich fish oil extract, to the Encapsulon particles further enhanced larval growth. Equivalent growth was obtained when Artemate was added to albumin or casein and when eicosapentaenoic acid was added to albumin. No growth occurred in larvae fed diets of single polyamino acids, oleic or linoleic acids, or starch. Growth equivalent to that achieved with Encapsulon particles was obtained with Artemate or EPA alone. Tests using fluorescent casein and beads to trace food uptake showed that nutrients entered the gut lumen within 5 min and the haemocoel within 1 h. Fluorescent fatty acids were incorporated into the membranes of the epidermal cells within the first 2 h after feeding. Epidermal cells of larvae fed diets enriched with PUFAs grew in height during the G1a period (late instar III and early instar IV), suggesting that early cell growth may trigger commitment to replication or expansion of the apical surface.