According to the Canadian Aquaculture Industry Alliance, to produce the highest quality farmed halibut, the very best adult female fish are selected each year as breeding stock.
Halibut broodstock are maintained in onshore tanks – where each female produces several batches of eggs each season for well over 100,000 eggs per kg of body weight. These eggs are then fertilised and incubated in the temperature-controlled tanks in a seawater hatchery.
Fertilised eggs hatch approximately 15 days after fertilisation. Upon hatching, the halibut larvae are transferred to the ‘larval’ tanks. The newly hatched larvae are only 6 and 7 mm in length.
During their first 50 days of life, the larvae receive nourishment from their yolk-sac. As the yolk sac is depleted, halibut farmers begin to feed the larvae a variety of small planktonic animals.
This diet of plankton is gradually replaced with a high quality pelleted feed designed specifically for halibut larvae after they reach about 0.3 grams.
After approximately 50 days, the halibut larvae undergo a metamorphosis during which both eyes migrate to one side and they display the flattened appearance of adult fish.
The young halibut are kept in circular tanks at the hatchery until they reach around 5 grams. The hatchery phase generally takes six to seven months. Following this they undergo a nursery phase until they reach a size of 100-200 grams and are ready for deployment in sea cages.
Upon reaching this size, most juveniles are transported via transport tanks on large trucks and barges to sea cage sites in the ocean or to land-based on-growing facilities.
To reach a targeted market size of 3-5 kg, it will take 24-36 months of on-growing where they are cared for and fed on a daily basis.
During the on-growing phase, halibut require around 1 to 1.5 kg of feed for every kg of weight gained.
Advances in Sexing
As mentioned above, female halibut are preferred for farming as they have a faster growth rate and grow bigger than males, meaning a quicker time to reach market size, thereby saving money.
Collaboration of scientists at the University of New Brunswick and the National Research Council, SABS researcher Debbie Martin-Robichaud isolated the precise timing of the tiny window of opportunity for sexual differentiation in the halibut, as well as determining the key to flipping the switch from female to male under controlled conditions.
The result is a broodstock that, while genetically female, can produce sperm. Fertilising eggs with this sperm guarantees that all the offspring will be female.
You may also be interested in:
- Life History and Habitat Characteristics Atlantic Halibut
- Mapping the Sex Determination Locus in Atlantic Halibut using RAD Sequencing
- Development of Broodstock diets for the Atlantic Halibut