Population dynamics, protein content, and lipid composition of Brachionus plicatilis fed artificial macroalgal detritus and Nannochloropsis sp. diets

Abstract

Microalgae are often used in the culture of the rotifer Brachionus plicatilis, which is widely used as live feed for larval fish. However, the cultivation of large quantities of unicellular microalgae to support rotifer population growth is a heavy burden on many hatcheries. The effects of artificial detritus (detritus) from the macroalgae Ulva pertusa, Undaria pinnatifida, and Chondrus ocellatus, on the population growth and nutritional content (amino acid and fatty acid composition) of B. plicatilis were evaluated as potential substitute diets. We used the microalgae Nannochloropsis sp. as comparative food. The results show that the nutritional value of the detritus from each macroalgal species is not as good as Nannochloropsis in terms of population growth, maximum population density, and population growth rate. However, when Nannochloropsis was mixed with the detritus from the other three macroalgae, for the resulting B. plicatilis populations maintained high levels and attained higher maximum population densities and population growth rates. The nutritional value of B. plicatilis fed U. pertusa detritus, specifically, the free amino acid, polyunsaturated fatty acid, and docosahexaenoic acid (DHA), were better than those fed with other diets. The DHA/eicosapentaenoic acid (EPA) ratio in rotifers fed U. pertusa detritus was the highest at 6.9 times higher than those fed Nannochloropsis. Therefore, the detritus of macroalgae, especially U. pertusa, is an appropriate substitute diet, at least partly, for the culture and dietary enrichment of B. plicatilis.