Changes in Blood Quality and Metabolites of Tachypleus tridentatus Under Captive Breeding Conditions

To reveal the effects of captive breeding on the physiology and metabolism of Tachypleus tridentatus, 90 T. tridentatus juveniles were selected, and blood samples were collected from each four times during a 90-day experiment. The blood quality was analysed by measuring Cu content. The results showed that, on Days 0, 30, 60 and 90, the Cu content in the blood of male juvenile T. tridentatus was 37.15, 22.62, 10.15 and 16.63 mg/L, respectively, with Days 30, 60 and 90 being 39.10%, 72.69% and 55.23% lower than Day 0. The Cu content in the blood of female T. tridentatus on Days 0, 30, 60 and 90 was 39.89, 20.27, 7.33 and 7.53 mg/L, respectively, with decreases of 45.44%, 80.26% and 81.11% on Days 30, 60 and 90 compared with Day 0. This indicated that the blood quality of male and female T. tridentatus decreased under captive breeding conditions. To measure metabolites, three male and three female T. tridentatus were selected and cultured under captive breeding conditions, and blood samples were collected on Days 0 and 30 and analysed using nontargeted metabolomics. Thirteen differentially expressed metabolites were identified, among which six significantly increased and seven significantly decreased. Among metabolic pathways, the sphingolipid metabolic pathways were notably affected. Changes in significant metabolites and metabolic pathways revealed nutritional deficiencies in protein, fat and vitamins. Insufficient nutrient supply was an important reason for the decline in blood quality of T. tridentatus under captive breeding conditions. In addition, four significantly different metabolites, namely, sphingosine, heptadecasphingosine, D-erythro-imidazolyl glycerophosphate and stearic acid, were selected as future target metabolites to analyse the nutritional demand of T. tridentatus under captive breeding conditions.