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Research Project: Developing and Refining Technologies for Sustainable Fish Growth in Closed Containment Systems

Location: Cool and Cold Water Aquaculture Research

Title: Crowder/grader units improve harvest efficiency in large circular tanks

item Summerfelt, Steven - Freshwater Institute
item Davidson, John - Freshwater Institute
item May, Travis - Freshwater Institute
item Crouse, Curtis - Freshwater Institute
item Waldrop, Thomas - Freshwater Institute

Submitted to: Global Aquaculture Advocate
Publication Type: Trade Journal
Publication Acceptance Date: 6/8/2015
Publication Date: 7/1/2015
Citation: Summerfelt, S.T., Davidson, J., May, T., Crouse, C., Waldrop, T. 2015. Crowder/grader units improve harvest efficiency in large circular tanks. Global Aquaculture Advocate. 18(4):66-68.

Interpretive Summary:

Technical Abstract: The use of larger and deeper tanks can reduce building, labor and other aquaculture production costs. However, the ability to grade and transfer large numbers of fish is more challenging when using large tanks. At The Conservation Fund Freshwater Institute, the authors have developed and evaluated in-tank crowders and top graders, as well as technologies to simplify the transfer of fish from the growout tanks to finishing/purging tanks. In a comparison of the effectiveness of a purse seine and a hinged clamshell to crowd fish in large tanks, the latter was easier to control and less stressful to salmonids. With a slotted bar rack in a side panel of the clamshell crowder, fish were simultaneously graded in size. A sidewall harvest box was developed to take advantage of the flow discharged through a sidewall drain box in a circular tank. To harvest fish crowded into this sidewall box, a normally vertical perforated door through the sidewall drain is opened, which allows crowded fish to rapidly flow into the sidewall drain box. A dewatering rack is also installed in the sidewall drain box to enable rapid fish harvest through the box while fish are dewatered. The fish outlet sluice channel, located opposite the sidewall box entry gate, provides a slope to its lower end. The fish outlet sluice channel is connected to a 20-30 cm diameter transfer hose, which is used to slide harvested fish to another location, such as a finishing/purging tank or palletized transfer tote. This technique has been used successfully to harvest rainbow trout, Arctic char, Atlantic salmon, and yellow perch.