Diurnal variation and effects of feeding on blood glucose in the giant tiger prawn, Penaeus monodon.

Previous studies on crustacea have demonstrated significant diurnal rhythms in blood glucose. However, glucose concentration in the blood of food-deprived Penaeus monodon, held in indoor or outdoor tanks, did not exhibit a diurnal rhythm under photoperiods of 8 h light and 16 h darkness (8L: 16D) or under a 13.5L: 9.5D photoperiod, with simulated or natural full moon conditions. Prawns held on photoperiods of constant light, 20L : 4D, 16L : 8D, 12L : 12D, 8L : 16D, 4L : 20D, or continuous darkness did not have significantly different mean blood glucose levels. Mean blood glucose levels varied between 0.77 and 1.39 mmol/L, depending on conditions. Pronounced and significant increases in blood glucose levels occurred within 20 min of feeding, with peak levels after 100 min. The rise in blood glucose level observed after feeding was independent of the eyestalks, and hence putative crustacean hyperglycaemic hormone, and was not from endogenous carbohydrate stores. Under appropriately controlled conditions, blood glucose concentrations can be used as an index of nutritional status in penaeid prawns.