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

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.