FROM RESEARCH TO COMMERCIALIZATION: PROGRESS OF A COD HATCHERY
J. Moir-1998
Bulletin of the Aquaculture Association of Canada, Edition 98-1: 36-38
Excerpts:
Sea Forest Plantation Ltd. (SFP) commissioned its hatchery in February 1996 and spawning began shortly after the hatchery opened. Spawning continued until the end of June when, with increasing water temperatures, all the remaining broodstock spawned. The company successfully raised 20,000 fry from 150,000 metamorphosed larvae using intensive green-water production techniques originally developed for sea bass and bream. Significant problems were experienced with bacterial infections during early larval rearing. Survival from each tank was 2,000 to 4,000 fry, regardless of the number of larvae stocked, suggesting that survival was food limited.
The annual production target of 2 million juveniles is based upon a survival rate of 10% from hatched larva to 10-g individual. There are three main phases in the hatchery cycle: egg incubation (20 days at 4 to 5 C), larval rearing (50 to 70 days at 12 C), and nursery rearing (approximately 90 days).
To meet the annual production projection, 2 million larvae must be hatched each month, which requires 3.3 million eggs (approximately 7 litres) based on a hatch rate of 65%. Nine hundred liters of incubation space is required for the eggs (three 300-L incubators). Larvae are initially stocked at 60 larvae/liter and four 8 m^3 larval rearing tanks are required. Water flows were calculated based on a maximum of 2 changes/day and starting with 1 change/day in the larval tanks.
In 1996, SFP used both rotifers and Artemia as food sources with a minimal supplementation of zooplankton collected in a UNIK filter. As a rule of thumb, prey densities are maintained at 5 rotifers/mL and the density of prey items is checked every two hours. For adequate feed production, the following requirements were determined from the 1996 feeding rates:
Rotifers maintained at a density of 200 million/larval tank
Total rotifer requirement is approximately 1 billion/day
Green water is supplied by 100,000 cells/mL of algae/day (T. isochrysis)
Algal requirement is 40 to 60 L of algae/tank or a total of 250 to 300 L/day, depending on algal counts
For rotifer culture, an additional 300 L of Nannochloropsis/day is required based on an estimated cell density of 45 x 10^6 cells/mL
Artemia are fed on demand based on residual Artemia in larval tanks
In order to meet the feed demands, significant modifications to both algal and rotifer production systems were required. The batch algal system was increased to a standing volume of 10^3 of algae in plastic bags. Light intensity was 20,000 lux at the bag surface and air was enriched with 1% CO2. These conditions yielded cultures of T. isochrysis with cell densities between 12 and 15 x 10^6 cells/mL, and Nannochloropsis cultures of 45 x 10^6 cells/mL. Approximately 10% of the total volume could be harvested on a daily basis.
A similar exercise for rotifer production was undertaken to arrive at the design criteria for the facility. SFP uses a standard 6-day cycle for rotifer production in which the population increases 3-fold over the 6 days. The following criteria were used to define the size of the rotifer facility:
Requirement to harvest 1 billion/day for feed and approximately 1 billion for restocking culture tanks
Stocking density in culture tanks of 500 rotifer/mL
Rotifers culture on a 6-day cycle
Rotifers grown in six 5 m^3 tanks
Egg collection and disinfection procedures are as follows:
Eggs are collected in 1000 micro m bags in an external collector
Eggs are removed once or twice daily, disinfected in 3% gluteraldehyde for 10 minutes, rinsed in filtered salt water, and placed in downwelling incubators
Dead eggs are removed daily, measured and discarded, and the remaining numbers noted
A second disinfection is undertaken in the incubator at 70 degree-days
Hatched larvae are transferred to larval culture tanks at 100% hatch
Once transferred to the larval tanks, larvae are closely monitored to ensure they are feeding and developing well. Larvae are measured on a regular basis to determine when the feed can change from rotifers to Artemia and ultimately to dry food. For the first 20 days, the tanks are siphoned to remove debris and dead algae every 5 days. As Artemia are introduced, water flows are increased to remove excess Artemia.
For the first 10 days of a production cycle larvae are fed rotifers enriched only with algae. As the larvae grow, some of the rotifers are enriched with Algamac and eventually all are enriched with Algamac. Artemia are enriched on a mixture of Algamac and DHA Selco. Larval rearing protocols are as follows:
Larval tanks are filled the day before transfer and the water is greened with algae
Water flow is set at 1 tank volume/day
Larvae are transferred to the tanks at a density of 60 to 70 larvae per liter
Algae is added daily for the first 3 weeks
Rotifers are fed beginning 1 to 3 days after transfer, once there is algae in the gut
Rotifer density is maintained at 5/mL
Tanks are illuminated for 24 hours per day with light intensity greater than 2000 lux at the water surface
Rotifer numbers are gradually increased as required
Enriched Artemia are added once larvae reach 6.5 mm
Dry food is introduced once 50% of the larvae are 12 mm or grater
Larvae are graded once the cohort reaches a minimum size of 13 mm
Once graded from the larval tanks the larvae are introduced to the nursery where weaning onto dry food is completed by gradually removing Artemia form their diet. Once fully weaned, the light intensity is reduced.
(Sea Forest Plantation Ltd., St. John's, NF, Canada)