Ornamental fish counting by non-imaging optical system for real-time applications

Abstract

One of the more labor-intensive operations in ornamental fish farms is fish counting. It is performed primarily when spawned fry are collected and introduced into grow-out tanks and when preparing fish for marketing. For various reasons such as cost and mode of operation of existing counting systems and inability to combine them with existing farm equipment, in many farms fish are counted manually despite time pressure and shortage of labor. An optical system for fish counting has been developed using hybrid non-imaging optics and an image-processing scheme to obtain an efficient single-detector counting system. The optical design includes a tailored field-stop aperture and a non-imaging scheme that reduces the influence of water fluctuations in a partially filled tube. The resultant increased signal-to-noise ratio enables overcoming the effects of water fluctuations. A prototype was tested with dummy and live fish. Counting errors with well-separated fish were less than 2%. Such a system can be used in similar operations with other small fish (e.g. edible fish hatcheries).