Hatchery technology has been developed so far for two Mediterranean species, sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata). Both of these technologies have already reached a commercial level, although many improvements in terms of survival and quality of fry have still to be achieved.
A marine hatchery requires high quality marine water, and brackish water can be useful as a complementary supply for the rearing stages. For pumping purposes, the hatchery should be located just above the sea level.
A marine hatchery includes basically a main building for the indoor fry production, and outdoor facilities for broodstock, plankton production and fry stocking.
Broodstock is maintained in outdoor tanks or ponds. Maturation of eggs can follow the natural cycles (spawning season during winter time for both species), or follow staggered cycles: the breeders are conditioned through photoperiodism and water temperature control and spawning can be achieved throughout the year.
Two methods are used for obtaining eggs:
induced spawning, by injection of hormones (usually human chorionic hormones).
After spawning, the floating eggs are collected automatically and transferred into the incubation tanks. At 18°C, incubation time for both species is about two days.
Rotifers (Brachionus plicatilis) and Artemia salina nauplii are produced as live food for larval stages of both sea bass and sea bream. Rotifer culture is carried out with the use of yeast and algae. For this purpose, several species of algae are cultured (genus Tetraselumis, Chlorella, Monochrysis, Isochrysis).
The culture of algae starts from pure strains and is carried out first in aseptic media and increasing volumes (0.5 to 6 l). As soon as a culture reaches the top of its concentration it is used to inoculate a larger volume culture. The mass production of algae is generally achieved in plastic bags of 100–400 l, but other methods are based on large outdoor tank (50–100 m3) cultures. The same scheme applies to rotifer culture, where the final mass production is generally carried out in 2–10m3 tanks.
Artemia nauplii are obtained through the incubation of cysts which are widely available commercially.
After hatching, larvae are reared in 2–5 m3 tanks at a temperature ranging from 16–24°C. Both cylindro-conic tanks of 2 m3 or larger circular tanks can be used. After 3–4 days from hatching, larvae begin to feed on rotifers for a duration of 5–10 days for sea bass and 15–25 days for sea bream. The larvae are then progressively fed on Artemia nauplii until the age of 30–45 days, depending on the temperatures used. At this stage larvae are transferred to larger tanks (6–15 m3), metamorphosis is achieved, and larvae are progressively conditioned to artificial dry feed. The same temperatures of 16–24°C apply also to this weaning stage. At the higher temperatures the fry populations reach an average weight of 1 g at about 3 months of age. Main technical data are given in Appendix 6.
For both larval rearing and weaning, water recirculating systems may be used, depending on the winter water temperatures, in order to save heating energy, especially if high rearing temperatures are applied.
Main technical/mechanical systems of a hatchery are:
pumps and PVC pipe systems, both for external water supply and recirculating systems
water treatment systems (sand filter, diatom filter, U.V. sterilization, biofilters for recirculating systems)
air blowers and supply pipeline
heating (both for air and water) and refrigeration (for staggered reproduction) systems
electrical plant and the emergency generator
Main service premises are:
workshop and store room
feed store and diet preparation room
laboratory and offices.