Turbot are generally a warm water marine fish with an optimum temperature through ongrowing, of around 18 C, much higher than ambient Norwegian seawater temperatures. However, one farm in Norway has found a solution to this problem. The Tinfoss A.S. hatchery is situated on an industrial site physically dwarfed by a huge plant extracting silica and manganese. The hatchery utilises the free waste water from this plant for its production of 450,000 turbot juveniles. Tinfoss has been producing turbot juveniles for 10 years and has recently begun to diversify into halibut production. Some turbot and halibut are on-grown at the site, but these are mainly for an extensive family selection program. However, Dr. Joachim Stoss, the director, explained that the fast growth rates obtained in recent years, have aroused interest in using the site for commercial on-growing. Spanish companies sold over 1,000 tonnes of Tinfoss-produced turbot in 1994 and the company broke even, expecting to make profits in 1995. On-growing is carried out in Spain by the Prodemar group, Tinfoss supplying 50% of their stock.
Although the farm is situated at the head of a fjord containing good quality seawater, its main asset is the supply of 1,000-1,500 m^3/h of free warm water from the industrial plant next door. This water is 10 C above ambient and is mixed with ambient water from the fjord to give the required temperatures. The water passes through a huge degasser, a mixer, where the temperature is adjusted, and a bank of 3 sand filters, before entering the hatchery or on-growing areas. Oxygen levels can be maintained at 10 ppm, but oxygen injection may be introduced in future to improve this.
There are 2 quarantine tanks designed for holding newly-caught wild broodstock and these are presently being used for a few large broodfish (1 of 25 kg) and some 2 year old juvenile halibut of about 1.5-2.0 kg. Water is ambient and they seem to survive the summer temperatures of 17 C. The broodstock are increasingly the offspring of selected families. They are maintained on constant temperature and fluctuating photo period regimes to give a year-round supply of eggs.
There are 14 egg incubators of 70L each (total=980L) with water flow and aeration and a temperature of 12-13 C. Hatched larvae are transferred to the larval rearing tanks prior to first feeding. Many larvae are sold to hatcheries for on-growing as Tinfoss produces 7 times more than they can use. Tinfoss larvae account for 70% of world farmed turbot. Larvae are cultured for the first 10 days in static green water with aeration and Isochrysis. Artemia are introduced at day 7 or 10. As the water flow is turned on the air is increased over the outlet screen to keep larvae away. Halibut first feeding tanks are 6 m^3 and larval rearing tanks are 3.5 m^2.
Weaning is carried out in 8 x 9 m^2 tanks and 36 x 1 m^2 tanks and is highly dependant on live feed quality during larval rearing. The length of the weaning overlap depends on the size variation, but is usually around 14 days. The nursery area contains 2 m^3 Rathbun tanks and is for fish of 10 g on-grown to 500 g. All fish are left undistrubed as much as possible, with only 1 feed/day. Halibut juveniles are fed constantly with auto feeders because it is not known yet what is the optimal number of daily feeds.
Rotifers are cultured in 4 x 2 m^3 tanks (total=8 m^3). They produce them all year round and export many to other hatcheries. They are cultured on a mixture of algae and yeast and are not enriched prior to feeding to the larvae as Tinfoss do not believe in enrichment of either rotifers or Artemia because it results in poor condition of the prey and increased bacterial numbers. Artemia are fed with a diet encouraging growth and condition. Algae is cultured in 200 L bags with lights on both sides. The species are Tetraselmis suecica (for low temperature halibut culture) and Isochrysis for turbot. The research unit is presently conducting investigations into microbiology, disease and monitoring the bacterial populations of rotifers, Artemia and fish.
(excerpts from article in Austasia Aquaculture Vol. 10, No 4, Sept./Oct.'96)
--------------------------------------------------------------------------------------