Evaluation of baseline haemolymph biochemistry, volume and total body energetics to determine an accurate condition index in the black tiger shrimp, Penaeus monodon

Crustaceans are exposed to a range of environmental factors that can impact their condition, physiological function and growth. Condition indices are broadly defined as the extent to which stored nutrient reserves allow normal physiological function and growth, but can also represent more than nutrition alone. There is currently no reliable indicator to non-destructively measure shrimp physiological or nutritional condition. In this study, haemolymph and biochemical indices were benchmarked against a range of physiological status condition indicators, including haemolymph biochemistry parameters and carcass traits, in fed and unfed sub-adult black tiger shrimp (Penaeus monodon) and across the moult cycle. Results based on fluorescent marker injection and analysis of recovered amounts showed that haemolymph volume was elevated immediately after the moult, but decreased significantly within 2 days and remained stable for the remainder of the inter-moult period. Brix index (Brix) strongly correlated with haemolymph biochemical, shrimp condition and carcass composition indices. These included haemolymph volume, total protein and triglycerides, as well as gross energy, hepatosomatic index (HSI) and body weight gain per moult. Overall, results demonstrated that Brix was the simplest, fastest and most cost-effective indicator to accurately and non-destructively estimate physiological condition in P. monodon. Given the correlations with a broad range of indices, Brix may represent a more holistic estimate of condition, incorporating multifactorial aspects of shrimp condition including moult cycle and nutrition. Additionally, the baseline measurements of metabolites across the moult and under starvation conditions improves our fundamental understanding of overall condition in P. monodon.