Feeding energetics and carbohydrate digestion of the juvenile New Zealand rock lobster, Jasus edwardsii
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
To enhance the on-growing of Jasus edwardsii in culture, it is important to understand the feeding physiology of juveniles. In crustaceans, there is a loss of energy and an increase in oxygen consumption (specific dynamic action (SDA)) associated with feeding. The present research measured the SDA of juvenile J. edwardsii fed either in the morning or at night held at 15°C. The present research also investigated important issues affecting the successful ongrowing of rock lobsters in culture, diet and nutrition. This was achieved by investigating carbohydrate digestion and metabolism. The present research also investigated the growth of juvenile J. edwardsii in response to three different algal carbohydrates; agar, carrageenans and alginate. Closed box respirometry was used to measure juvenile lobsters oxygen consumption (MO₂) and ammonia excretion. Juveniles exhibited a nocturnal rhythm in both MO₂ and ammonia excretion. The factorial rise in MO₂ (1.58±0.03 times) for lobsters fed in the morning was significantly less than lobsters fed at night (1.80±0.01 times). Lobsters fed in the morning had a significantly shorter SDA (30±1.2 h) response compared to lobsters fed at night (36±1 h). Energy loss as a result of digestion was less for lobsters fed in the morning. Therefore, if juvenile J. edwardsii are fed in the morning, they could optimise the energy content of the meal and this could result in increased growth. At 18°C, over 80 days juvenile J. edwardsii that were fed squid in the morning had a specific growth rate (SGR) of0.92±0.07 %body weight d-¹ and grew faster than lobsters that were fed at night (SGR = 0.76±0.01 %bw d-¹). Morning fed lobsters had a percent weight gain (%WG) of 107.0±3.1%, which was significantly higher than lobsters fed at night (%WG = 78.4±3.1 %). Survival was also greater for morning fed lobsters (50%) than night fed lobsters (25%). The SDA was used as a tool to determine if juvenile J. edwardsii could utilise a range of general carbohydrates from simple monosaccharides (glucose, fructose), disaccharides (maltose, sucrose) and polysaccharides (glycogen) (general carbohydrates). Three algal binding agents (polysaccharides) were also tested; agar, carrageenans and alginate (algal carbohydrates). For lobsters fed the general carbohydrates, oxygen consumption increased to a peak followed by a slow decline back to pre-feeding levels. The more complex the carbohydrate, the greater the oxygen consumption profile. However, when lobsters were fed on algal carbohydrates they did not exhibit this trend and had similar oxygen consumption profiles to unfed lobsters. Oxygen consumption magnitudes were significantly higher in lobsters fed a meal of glycogen, sucrose, maltose and agar than unfed lobsters. If juvenile J. edwardsii were able to digest and utilise carbohydrates, there should have been a rise in haemolymph glucose concentration following feeding. The results confirm that juvenile J.edwardsii can digest all the general carbohydrates, but require more energy to digest and metabolise glycogen and sucrose. Lobsters fed agar had a significantly higher haemolymph glucose concentration than unfed lobsters. This was the only algal carbohydrate to exhibit this response as alginate and carrageenans had similar response to unfed. These results suggest that the SDA can be used as a technique for determining carbohydrate digestion in juvenile J. edwardsii and that the magnitude of the response is the most sensitive SDA parameter. Growth rates of juvenile J. edwardsii fed algal carbohydrates were measured at 18°C, over 80 days. Growth of lobsters fed fresh blue mussels (Mytilus galloprovincialis) was higher (SGR =1.64±0.02 %bw d-¹) than any of those produced with the algal carbohydrate diets. Lobsters fed a diet of mussels also had higher survival rates (87%). Growth rates were similar amongst the algal carbohydrates (agar SGR = 0.91±0.10 %bw d-¹; carrageenans SGR = 1.14±0.04 %bw d-¹; alginate SGR = 0.97±0.35 %bw d-¹) but were superior to lobsters fed a diet of squid (SGR =0.76±0.01 %bw d-¹). The survival of lobsters fed an agar (50%) diet was significantly higher than those fed carrageenans (37.5%) and alginate (25%) diets. Based on these results juvenile J. edwarsii can digest and utilise agar more efficiently than carrageenans and alginate. The growth experiment, oxygen consumption and haemolymph glucose results from the present research will aid in the development of a nutritional, cost effective diet for the successful aquaculture of J. edwardsii.