 Manipulation of Environmental Parameters and Rearing Conditions
Growth and sexual maturation are highly complex processes in fish
and are influenced by numerous factors. Of prime interest to the
fish farming industry are the factors that may be controlled under
culture conditions in order to optimise production. The manipulation
of environmental factors and rearing conditions such as temperature,
salinity, photoperiod, and feed ration is currently used as a means
to manage these physiological processes in farmed fish.
However, detailed environmental requirements of many marine
species through the on-growing phase are poorly understood due to
the lack of controlled experimental work. Particularly, information
regarding the effect of simultaneous manipulation of these
environmental factors is limited, although the interaction effect of
any of these factors may well be as important as any single factor.
The research programmes at Akvaplan-niva concentrate heavily on
the investigation of the effects of environmental parameters on fish
reared in captivity, with the primary objective of identifying the
most favourable rearing environments and practices, ultimately
increasing the efficiency and overall productivity of the industry.
Of all environmental factors that influence growth in fish,
temperature is the single most dominant, acting as a
rate-controlling factor for all chemical processes while
photoperiod, on the other hand, effects growth and sexual maturation
through the regulation of the endogenous rhythms of the fish.
Changes in salinity or feeding regimes may also be used to influence
the growth of fish through the metabolic response they induce.
Akvaplan-niva has been involved in several projects investigating
the solitary and interactive effects of environmental manipulation
on basic physiological processes and how these effects may be
capitalised upon in a commercial setting.
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The use of “temperature-steps”
i.e., water temperature is gradually reduced with increasing
body size, in the rearing of halibut, turbot, and cod has been
shown to improve long-term growth as compared to rearing under a
constant temperature.
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The rearing of cod juveniles under
specially designed temperature and photoperiod regimes has been
shown to induce positive long-term changes in growth patterns.
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The combined use of photoperiod
manipulation coupled with a reduction in water temperature has
been shown to induce early spawning in Atlantic salmon
broodstock groups.
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The interactive effects of
temperature and salinity have been exploited to induce improved
growth and feed conversion in turbot.
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The application of combined
photoperiod and fasting regimes has been used to reduce feed
costs and improve slaughter quality in halibut without affecting
growth. A similar study on cod is underway
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The use of zooplankton during the
start feeding of cod larvae has been found to result in an
increase in body weight, traceable until the fish are harvested
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