Egg Storage and Hatching Equipment
The main purpose of units for storage and/or hatching of eggs is to create a restricted area where the eggs can grow under optimal conditions. Separate units can be used for storage and hatching, or the same unit can be used for both purposes. It is also possible to combine the hatching equipment with later holding of fry and eventually also for first feeding. Units for the incubation of eggs are often called incubators.
In the storage unit, the eggs must be supplied with sufficient new water to meet their oxygen requirements and remove metabolic waste products. Continuous addition of new water will also achieve the necessary water exchange that is essential to inhibit the growth of fungus which may increase mortality. In addition, the quality of the water is of great importance at the egg stage. As the oxygen requirement is low at the egg stage, it is possible to not have a continuous supply of water, but to exchange water in batches, provided that there is no fungus problem or an antifungal agent is added to the water. Addition of air through diffusers may also be used to supply oxygen.
The design and function of the units depends on how the eggs need to be stored and the intensity of production. Eggs from different species have different storage requirements. Some prefer to lie on the bottom or on/in a bottom substrate; others prefers to stay pelagic in the free water mass, while others again are stored inside the females: under wild conditions, for instance, Tilapia stores the eggs in the mouth and initially the wolf fish stores them inside the ‘belly’ for fertilisation before laying demersal eggs. Salmonids and catfish are representatives of the first group where eggs prefer to stay on the bottom, while several marine species such as cod and halibut and several freshwater species belong to the second group. Under farming conditions, however, one species may be adapted to use a rearing system different to that used in the wild, such as holding pelagic eggs on a bottom substrate. Normally, systems in which the eggs lie on the bottom or on a bottom substrate are easiest to build and control. There are also differences in how the egg lies, because some species have single eggs, while in others the eggs lie together in a matrix or with a ‘cover’ around the egg batch. Egg size varies significantly between species and this is also of major importance when designing storage and hatching units with the required water supply; the task is more difficult with smaller eggs.
Egg production can be separated into intensive and extensive farming, and this also influences the design of the equipment. For more extensive farming, ponds, net pens or cages may be used, but of course the production per volume unit will be reduced. If using extensive systems, the eggs can be collected and put into intensive hatching systems or the hatching can be performed in the extensive system, depending on production strategy. Egg production is normally based on artificial spawning, but egg production can also be based on collecting wild eggs that are introduced into extensive or intensive farming systems.