Nutrition and broodstock conditioning of the New Zealand Pipi, Paphies australis
The New Zealand pipi, Paphies australis, occurs widely around the coast of New Zealand and belonging to the family Mesodesmatidae. Pipi form a part of the recreational bivalve fishery, and there is also an annual restriction of the total commercial harvest. Previous investigations have examined the biological and ecological aspects of pipi in the wild. However, neither of them studied the nutritional requirements of pipi under hatchery conditions. This thesis discusses the feeding requirements of pipi collected from Waiwera Beach and Onehunga Harbour, during their growing and maturing stages. A series of studies on the cell clearance rates, feeding trials, proximate analysis, and broodstock conditioning of pipi clams were conducted over 15 months (September 2008 until December 2009) at the AUT Aquaculture Laboratory. In the cell clearance rates study, the rates for microalgal diets in descending order were Thalassiosira pseudonana > Isochrysis galbana > Chaetoceros muelleri > Tetraselmis suecica > Pavlova lutheri. It is inferred that pipi are capable of filtering a variety of microalgal species while at the same time being a selective filter feeder. The same microalgal species tested in the aforementioned study were fed to pipi of different size classes (spat, juveniles, and adults) in the feeding trials experiment. Three processed diets (baker's yeast, wheat flour, and corn flour) also were tested on the pipi clams. This study was carried out to test the effect of different diets on growth and survivality, and body composition of spat, juvenile, and adult pipi. There were positive relationships between the growth performance (length and weight) and dietary lipid content for spat and juveniles. For adult pipi, the carbohydrate content in the diets was positively related to pipi shell growth. However, proximate analyses of adult pipi at the end of the experiment indicated an overall depletion of carbohydrates in the tissues, while proteins and lipids were accumulated. These results suggest that the gonadal development have initiated during the breeding season. Based on the results of the present study, it is suggested that baker's yeast would be a good substitute of spat and juvenile feeds, and wheat and corn flours would be good substitutes for adult feeds. In the conditioning experiment, broodstock pipi were conditioned with three different diets: exclusively P. lutheri, exclusively corn flour, and a mixed diet composed of P. lutheri and corn flour in 1:1 ration. On days 21 and 28, following the conditioning period, broodstock were induced to spawn by temperature shock treatment. Although both spawning induction trials failed to bring broodstock pipi into spawning condition, maturity was apparent for brooodstock fed the mixed diet of P. lutheri and corn flour, indicating that P.lutheri-corn flour may be a better food source compared to P. lutheri or corn flour alone for pipi broodstock conditioning.