Collection of feed spill and faeces from tank outlet. The FOGAS project

Summary

Feed spill collection and stripping of faeces are common tasks in fish nutritional trials at Nofima’s Research Station for Sustainable Aquaculture at Sunndalsøra. The established method for collection of feed spill requires manual work and is time consuming. A simpler method for feed spill collection, which also allowed collection of faeces at the tank outlet, was developed. The result was a demonstrator denoted ‘Spillbox’. The Spillbox, with a vertical screen with horizontal wires, was placed at the tank outlet. Uneaten feed was collected in a container separated from the water flow. By using compressed air, faeces were collected in another container, also kept away from the outlet water. In the recovery test (n=4) with one feed, 87 % of the feed was collected. Feeding salmon (biomass 46 kg) one diet containing Y2O3, faeces was collected for 24 hours, resulting in 31 g of faeces (mean, n=3). Apparent digestibility measured from faeces collected with the Spillbox resulted in very small variation among replicates, and digestibility of dry matter and energy was very similar to data obtained by stripping. The calculated digestibility of fat and nitrogen (protein) deviated from data obtained with stripping. The Spillbox worked satisfactory for its purpose with the feed type used. For further documentation of the Spillbox for feed collection, testing with several pellet sizes and physical pellet qualities is required. For collection of faeces, it is recommended to investigate the deviation in AD values obtained with the Spillbox method and the stripping method. Faeces quality varies with feed, and these initial tests indicated that the system may be controlled and adjusted for varying faeces qualities. However, a certain firmness of the faecal particles is required for collection with the Spillbox. It is relevant to upscale and adapt the Spillbox for collection and reuse of uneaten feed, and collection of faecal matter (sludge) in commercial land-based salmon farming. Theoretic mass balance and amount of sludge produced in commercial farming in different situations was calculated. In conclusion, the Spillbox could be used for collection of uneaten feed and for collection of faeces for digestibility measurements for the feed tested. Some optimization and adjustment of the system when used under different conditions, and documentation of its accuracy using several feed types is recommended.