The effect of dietary carbohydrate on the appetite revival and glucose metabolism of juveniles of the spiny lobster, Jasus edwardsii

The inclusion of dietary carbohydrates has the potential to deliver more cost-effective formulated diets for spiny lobsters, however, the effect of carbohydrates on feeding and glucose metabolism is poorly understood. Poor appetite revival for lobster fed on formulated diets has been identified as a major factor reducing growth rates of the spiny lobster, Jasus edwardsii. The effect of inclusion levels of gelatinised maize starch (LCHO, 70 g kg⁻¹; MCHO, 270 g kg⁻¹; and HCHO, 470 g kg⁻¹) on the feed intake, appetite revival, haemolymph glucose, as well as the soluble protein, glucose, glycogen and the activity of digestive enzymes of the digestive gland (i.e., total protease, trypsin, α-amylase, and α-glucosidase) was investigated in juveniles (~25 g) of the spiny lobster, J. edwardsii. Lobsters were sampled at 24 h and 72 h after their last meal to understand the effect of short-term starvation on the use of digestive gland glycogen as an energy reserve. Including up to 470 g kg⁻¹ of gelatinised maize starch had a positive effect on the dry matter intake over 5 h (LCHO, 1.14±0.04% BW; and HCHO, 1.29±0.04% BW) and did not affect appetite revival rate (3.77%h⁻¹ for the three diets) despite the prolonged hyperglycaemia (peak for LCHO at 7 h=2.13±0.05; and peak for HCHO at 24 h=4.99±0.53 mM). While haemolymph glucose appears poorly regulated and utilised for energy during feeding, it is stored as glycogen (LCHO, 4.57±1.44 mg g⁻¹; and HCHO, 46.00±7.62 mg g⁻¹) and this reserve is utilised during short-term food deprivation (between 24 h and 72 h), while soluble protein remains constant. This was supported by an increase in the specific activity of α-amylase (0.57±0.04 at 24 h and 0.71±0.06 U mg⁻¹ at 72 h) during short-term starvation, while total protease decreased (76.24±4.16 to 61.10±3.80 U mg⁻¹). It is concluded that digestible carbohydrates have a positive effect on feeding in this lobster species and may play an important role in maintaining nutritional condition during short-term periods of food shortage.