The presence of endogenous l-carnitine in live foods used for larviculture

Abstract

The endogenous presence of l-carnitine (free and esterified l-carnitine) in live foods used for larviculture was determined by a method of HPLC assay based on enzymatic reactions. Two strains of marine rotifers ( Brachionus rotundiformis and Brachionus plicatilis), freshwater Cladocera ( Moina macrocopa), six populations of Artemia and two species of microalgae ( Nannochloropsis oculata and Chlorella vulgaris) were cultured and tested. Results showed that B. rotundiformis and B. plicatilis have 161–504 μg g − 1 DW and 338–393 μg g − 1 DW total l-carnitine under varying culture conditions, respectively. The study further revealed that temperature shifts (24 h, 5–15 °C lower) did not affect l-carnitine content in the two strains, whereas, culture temperature and starvation remarkably influenced l-carnitine content in B. rotundiformis. These effects were accounted for by a significantly lower and a significantly higher l-carnitine content ( P < 0.05) in the groups under low culture temperature (15 °C) without 24 h starvation and high culture temperature (30 °C) with 24 h starvation, respectively. In M. macrocopa, 386 μg g − 1 DW total l-carnitine was detected. The total l-carnitine levels, ranging from 220 to 493 μg g − 1 DW, had significant ( P < 0.05) variability in newly hatched Artemia nauplii from samples of various populations. The total l-carnitine contents in microalgae N. oculata and C. vulgaris have no significant ( P > 0.05) differences between condensed commercial products, but significant ( P < 0.05) differences were observed in laboratory cultured N. oculata, ranging from 91 to 314 μg g − 1 DW, associated with different light intensities and photoperiods. These results indicated that endogenous l-carnitine is quite variable in live foods depending on their physiological status, and is significantly influenced by environmental factors, such as culture temperature, starvation and light conditions.