Egg Storage and Hatching Equipment
Introduction
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.
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