Grading machines perform successfully with catfish

African catfish are a popular aquaculture species, but until now they have been difficult to grade automatically. Fischtechnik International Engineering GmbH (FTIE) has recently conducted a successful grading trial for African catfish and can now recommend its own grading machines for use with the species.

African catfish (Clarias gariepinus) are robust, grow rapidly and have modest requirements concerning protein levels in feed or water quality. In particular the species' ability to breathe a certain amount of atmospheric oxygen makes higher population concentrations possible without the need for technical oxygen or complex water aeration. All these factors make the African catfish a popular species for use in commercial aquaculture.

Fish reared in aquaculture systems have to be graded regularly according to size. Traditional aquaculture species such as trout or salmon are easy to grade since their long history of commercial breeding has resulted in a high uniformity of shape and size. This is not true for the African catfish, however. Fish of the same weight can vary greatly in body shape, fatness and length, making it difficult to sort them into groups and posing particular challenges for the grading process. A further problem with the African catfish is its anatomy. However robust the fish may be when it comes to the conditions it can tolerate, its large head and scaleless skin make it particularly sensitive during grading or harvesting. For this reason, the fish have often been graded laboriously by hand, even in large quantities.

Grading machines manufactured by Fischtechnik International Engineering GmbH use a special belt grading system which makes them very precise and gentle to the fish. This prompted the idea of running a trial with African catfish. Tests with various models showed that the large variables of the Fischtechnik machines make them well suited to handling catfish. The fish came through the grading process completely unharmed and showed excellent vigour. The accuracy of grading was also good.

Following minor modifications to the machinery to suit the species, Fischtechnik can recommend its grading machines for use with African catfish.

All commercially significant fish species can be graded with either the standard model or customised versions of Fischtechnik grading machines. The range comprises models capable of grading fish weighing between 5g and 3kg in up to five sizes. Standard machines have a handling capacity of between 1 and 3 tonnes per hour. Custom-built models can handle up to 10 tonnes.

Fischtechnik International Engineering GmbH specialises in systems for intensive, low environmental impact fish farming. Chief focus is recirculation aquaculture systems that use a minimum of water and electricity. Close links to research institutes, universities and specialised companies all over the world ensure state of the art systems of the highest technical and biotechnical standard.