Biomonitoring of the river pufferfish, Takifugu obscurus in aquaculture at different rearing densities using stress-related genes

The river pufferfish Takifugu obscurus is one of the most valuable aquaculture species in South Korea and China. To analyse the effect of rearing densities in the aquaculture of this species, we performed an experiment where T. obscurus was reared for 3months after hatching at different initial rearing densities (10 fishL(-1), 20 fishL(-1), and 25 fishL(-1)) which are similar to rearing densities in aquaculture (10-15 fishL(-1)). The growth of the high density group (25 fishL(-1)) was significantly slower than that of the low density group. To determine biomarkers for stress under conditions of high rearing density, we chose six stress-related genes (heat shock proteins (HSPs) 70 and 90, metallothionein (MT), cytochrome P450 1A (CYP1A), glucocorticoid receptor (GCR) and phosphoenolpyruvate carboxykinase (PEPCK) and evaluated their expression by real-time reverse transcript polymerase chain reaction (real-time RT-PCR). In the high density group, we observed significant up-regulation of genes encoding HSPs 70 and 90, MT, CYP1A, and PEPCK in liver and brain, but no up-regulation of the GCR. In particular, expression of HSP70, MT and CYP1A was up-regulated in a tissue-specific pattern. Our results demonstrate that growth retardation at high initial rearing densities is associated with stress-induced gene expression. These findings further indicate that molecular biomarkers can be useful to determine the optimal rearing conditions with respect to densities of pufferfish culture.