Download Manipulating Fish Behaviour

FBE201: Summer 2012
Manipulating Fish Behaviour
Introduction
• Economically driven culture systems attempt
to maximize yields by maintaining fish at high densities,
minimizing husbandry requirements
keeping the fish farm environment as
basic as possible
using feeds which are artificial both in
appearance and composition
Introduction
• Some aspects of natural behaviour of the fish
are retained and there are changes in
behaviour
• Either improvement or optimization of
efficiencies could be expected.
• Integrating the behavioural requirements of a
culture species with other biological aspects
of the management protocols
Environmental control
Cage/tank design
• Constrain swimming behaviour of fish in the farm
environment
• Square cages slow fish down as they adjust their
course when encountering corners
• Circular cages may enhance schooling behaviour
and uninterrupted swimming action
• Practical considerations of cages should join
together in a more cost-effective way (i.e. units of
square or rectangular cages).
Environmental control
Cage/tank design
• Reduce surface exposure by high-density
feeding strategies or the development of subsurface feeding.
• Provide cages with shading for a more effective
utilization of cage volume
• Artificial lighting is a general modifier of
behaviour, like foraging, sexual maturation,
nocturnal schooling
Environmental control
Water quality
• Farmed fishes exhibit strong thermal
behaviour, by maintaining relatively constant
body temperatures
• Temperature; maximize food conversion and
growth
• Temperature & salinity; influence position in
water column
Feeding patterns
• Any feeding protocol seeks to optimize FCR
through the modification of feeding regimes, and
by maximizing the amount of food being taken,
thereby minimizing waste.
• Commercial feeding schedules through daylight
hours
• Diel rhythmus apparently driven by photoperiod
• Strongly influenced by temperature variation
• May cause a switch from diurnal to nocturnal
feeding pattern.
Feeding patterns
Presentation control
• Spatial and temporal distribution
• Hand-feeding, where a visual judgment of fish
behaviour is used to assess hunger level.
• Most farmed fish species show an adaptive
flexibility in their feeding behaviour.
• Demand feeders are controlled by the feeding
behaviour at either the individual or the group
level.
• Self-feeders are so termed because they rely on
the individual feeding activity of the fish
actuating a manual or electronic trigger.
Feeding patterns
Dietary characteristics
• Visual characteristics such as shape, size,
colour and movement,
• Gustatory properties such as texture, taste
and smell.
• Artificial diet capture and ingestion can be
improved by enhancing the fish’s visual
perception of pellets
Feeding patterns
Dietary characteristics
• Fish offered diets which contrast well with
background colours will capture proportionately
more pellets and, as a result, grow faster.
• Shape may also be of importance, but
manipulating shape will also affect the movement
profiles of pellets through water.
• Long pellets tend to tumble in the water column,
whereas round ones sink much faster in a rolling
motion.
Feeding patterns
Dietary characteristics
• Addition of gustatory stimulants (e.g. proteins,
amino acids, vitamins, minerals, fish oils) to
diets, enhance the dietary perception of a
pellet.
• Other dietary constituents can be used as
chemo-attractants, enhancing both attraction
and taste, and several amino acids now
incorporated in to commercial diets for these
reasons.
Feeding patterns
Photpperiod
• If the fish are reliant on visual stimuli then the
photoperiod provides a finite window for
feeding but it also contributes information
relating to time of day and time of season.
• Continuous illumination has effect on
schooling behavior and sexual maturation.
• It also can provide enhance feeding times,
resulting in faster growth rates.
Feeding patterns
Dominance regulation
• Social hierarchy formation may lead to depressed
feeding in subordinates, resulting in growth
suppression.
• Temporal (localized) feeding enables domination
of some fish over lower ranking individuals
• Rate of aggression increase as the number of fish
per tank or cage increase
• Adoption of a feeding protocol combining a high
fish density and moderate food dispersal within
limits