ARE BUTTERFISH a viable farmed product?
BY PHILIP HEATH AND SARAH ALLEN NATIONAL INSTITUTE OF WATER AND ATMOSPHERIC RESEARCH
A small adult butterfish, capable of spawning
Young butterfish five months after hatching
last few years doing preliminary growth assessments on captive juvenile butterfi sh and rearing larvae at the hatchery produced from wild butterfi sh broodstock. Butterfi sh (Odax pullus), otherwise known as marari
or greenbone (after the distinctive colour of their bright, bluish-green bones), are found all around the New Zealand coast, particularly in and south of Cook Strait and around Wellington. They have been caught commercially in New Zealand for over a century in set nets. The juvenile fi sh were easily captured in fi ne mesh nets
Larval butterfish enjoy their first feed 20 days after fertilisation
F
ish farmers and environmentalists share concerns about the sustainability of an industry dependent on fi shmeal in fi sh pellets to survive. Finding alternative feed sources fast is vital for the economic and environmental survival of fi sh farming. Alternatively, consideration must be given to farming species that don't require fi shmeal in their diets. One such species is butterfi sh, a large, herbivorous cool water marine fi sh endemic to New Zealand. To assess the aquacultural potential of butterfi sh, NIWA researchers at Mahanga Bay in Wellington have spent the
12 ■ NZ AQUACULTURE ■ SEPTEMBER/OCTOBER 2011
and brought alive to tanks at Mahanga Bay. Once acclimatised to their new home, the hardy fi sh were weaned onto specially formulated pellet diets. Butterfi sh graze on seaweed in the wild, so training them to eat pellets involved two steps. The fi rst was teaching them to eat particulate diets by offering them peas, corn and pieces of mussel before switching to the pellets. Observations of butterfi sh feeding indicate they are both visual and tactile feeders, initially looking at a pellet, then feeling it with their mouths before fi nally deciding whether or not to ingest it. With this in mind, NIWA researchers developed a pellet containing pea fl our, maize fl our, seaweed meal and mussel meal as the main ingredients to entice the fi sh to feed. Growth trials showed no signifi cant difference between
growth on the formulated diets alone, or when supplemented with seaweed or mussels. Growth rates were generally quite low at 0.2 percent or around 0.9g a day and food wastage was high, with the fi sh consuming a little over 40 percent of the food offered to them. Wild-caught juveniles also tended to suffer sea lice infestations which required regular treatment with formalin. Many of the larger wild-caught fi sh also had large lice resident in their mouths. Having investigated the challenges of rearing wild-caught juvenile fi sh, the team turned to how butterfi sh would
