Experimental Study On The Technology Of Fish Grading And Harvesting For Cage Mariculture

This paper describes the development situation of deep sea anti-storm cage mariculture in China. On this basis, a flexible fish size grading system and a live fish harvesting machine, which can be used as facilities and equipment fitted for deep sea anti-storm cage mariculture, were designed and manufactured.In fish mariculture production, fish body sizes varied after a certain period of farming due to the differences of fish fry sizes and the feed taking abilities of individual fish. Sometimes, the body weight of the heaviest fish could be hundreds of grams heavier than that of the smallest one. In order to select the fish size in the same range of body weight during culture and harvesting, a flexible fish grading system was designed and manufactured based on the selective principle of fishing gears. The system, consisting of a fish separation panel, a separation net, ropes and other necessary fittings, was strong, flexible, safe and maneuverable. By using the grading system, fish size can be selected effectively. Referring to the vacuum and negative pressure theory, a fish harvesting machine was also designed and manufactured. It consisted mainly of a vacuum fish tank, a vacuum pump, a water line limitation switch, an automatic circuit control box, electromagnetic valves and dynamoelectric valves, watertight gate and rubber pipe. Moreover the harvesting machine had no damage on fish and was fit for fish harvesting in the deep sea cage, and could reduce manpower effectively.83 pieces of Sebastes schlegeli and 86 pieces of Japanese sea bass were randomly selected from the cage. Weight and size were measured. And two linear regression equations could be got to show the relation between weight and body size: W=0.1157L2.1906, R2=0.9266 (for Sebastes schlegeli) and W=0.1634L2.165, R2=0.9694 (for Japanese sea bass ).Referring to the two equations, we could get the result that a aperture of 44mm was fit to select fish Sebastes schlegeli with a body weight of 0.5kg. In an experiment, 800 pieces of Sebastes schlegeli less than 0.4kg and 200 pieces more than 0.6kg were prepared in a cage of 4m X 4m X 4m. Statistical data showed that 90.33% of all the small fish, which could escape out, was separated by the grading system after 10 minutes separation. In a cage of 50m in circumference, the test result showed that the average body weight of the big size fish remained in the grading net was 0.13 kg more than that of fish without sizing grade.Another very valuable use for the Flexi-Panel is in removing unwanted wild fish. In a cage where Sebastes schlegeli had been cultured for 6 months, a separation panel with aperture of 30 mm was used to remove the unwanted fish and 58.6 kg of wild fish were caught.Furthermore, different sizes offish can be selected by changing the flexible panel with different apertures.The trial harvesting results showed that the harvesting capacity of the machine can be up to 20 tons per hour when the proportion of fish and water reaches one to one. Moreover the harvesting machine has no damage on fish and reveals stable, reliable performance and high degree of automation. It is proved that the machine can be widely used in cage farming industry.