Fish Hatchery Management - fisheries & aquaculture

HATCHERY OPERATIONSMost fish diseases are water-borne and are readily transferred from onerearing unit to another by equipment such as brushes, seines, and dip nets.All equipment used in handling and moving fish can be easily sanitized bydipping and rinsing it in a disinfectant such as Roccal, Hyamine, or sodiumhypochlorite. Solutions of these chemicals can be placed in containersat various locations around the hatchery. Separate equipment should beprovided for handling small fish in the hatchery building and should notbe used with larger fish in the outside rearing units. Detailed proceduresfor decontaminating hatchery facilities and equipment are presented inChapter 5.Dead and dying fish are a Potential source of disease organisms andshould be removed daily. Empty rearing units should be cleaned andtreated with a strong solution of disinfectant and then flushed before beingrestocked. Direct sunshine and drying also can help sanitize rearing units.If possible, ponds and raceways should be allowed to air-dry in the sun forseveral weeks before they are restocked. To prevent long-term buildup oforganic matter, ponds typically are dried and left fallow for two to fivemonths after each harvest. Manytimes, the pond bottoms are disked,allowing the organic matter to be oxidized more quickly. After the pondsoil has been sun-baked, remaining organic material will not be releasedeasily when the pond is reflooded.Disinfection of warmwater fish ponds is a process by which one or moreundesirable forms of plant and animal life are eliminated from the environment.It may be desirable for several reasons: disease control; eliminationof animal competitors; destruction of aquatic weeds, among others. Disinfectionmay be either partial or complete, according to the degree to whichall llfe is eliminated. It is impractical, if not impossible, to achieve completedisinfection of eathern ponds.Disinfection of ponds with lime is a common practice, especially in Europe.This is particularly useful for killing fish parasites and their intermediatehosts (mainly snails), although it will also destroy insects, other invertebrates,and shallow rooted water plants for a few weeks. Calcium oxideor calcium hydroxide are recommended; the latter is easier to obtainand less caustic. Lime may be applied either to a full or dewatered pond(so long as the bottom is wet) ; in either case, the lime penetrates the pondsoil less than an inch. It is most important that the lime be applied evenlyacross the pond, and mechanized application is better for this than manualdistribution. Except for the smallest ponds, equipment for applying limemust be floated. This means that at least some water must be in the ponds,even though lime is most effective when spread over dewatered soils.Lime makes water alkaline. If the pH is raised above 10, much aquaticlife will be killed; above ll, nearly all of it. Application rates of 1,000 to2,500 pounds of lime per acre will achieve such high pH values. Appropriaterates within this range depend on the water chemistry of particular