| Summary: | The efficiency with which feed is converted to fish flesh is a prime problem for the aquaculture
industry. In the practical sense, feed conversion ratio (FCR) refers to the amount of feed that is
dispensed to the fish relative to the amount of weight gained. The present research dealt with
the possibility of extending the feeding opportunity of caged fish from the current restricted
area near the cage surface to the larger volume of the cage as a technique for reducing this ratio
and increasing feeding rate.
Procedures were developed to control both feeding rate and pellet loss after inspecting
feeding behaviour using underwater-cameras. Tests indicated that BioFCR in cameramonitored
cages were lower than in surface-fed cages. Spatial homogeneity in feeding
(uniform feeding) was seldom observed in both camera-monitored and surface-fed cages.
Pellet wastage was high if fish were surface-fed or fed to a predetermined ration. One
explanation for the lack of feeding uniformity was poor visibility of feed pellets towards the
cage bottom.
The effects of using a contrast-enhanced pellets and light intensity on feeding patterns
were examined while feeding Atlantic salmon (Salmo salar L.) using the previously developed
camera-monitored feeding method. The contrast-enhanced pellet tested (silver coated) was
chosen after a series of laboratory-based fish detectability experiments had been conducted.
The silver pellets were 41% more detectable than a conventional pellet to a human observer.
Neither the use of conventional nor silver pellets permitted uniform feeding, as fish tended to
feed in groups. Pellet discharge rate decreased as stocking density and light intensity increased,
and was lower for silver pellets. Fish fed silver pellets preferred to feed near the cage bottom,
and this preference increased the likelihood of pellet wastage. Feed discharge rate was,
therefore, reduced in cages fed silver pellets to keep fish off the cage bottom.
Overall, camera-monitored feeding is more effective than surface feeding, as FCR is
improved and feeding rate can be optimised. Contrast-enhanced pellets offer fish a choice of
where to eat. Light intensity affects spatial homogeneity of feeding, with the highest level of
homogeneity under conditions of low light intensity and good water visibility.
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