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New strategies for feeding salmonids : video monitoring and contrast enhancement of feed pellets Ang, Keng Pee

Abstract

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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