Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2008
Publication Date: 3/1/2009
Publication URL: http://handle.nal.usda.gov/10113/55801
Citation: Summerfelt, S.T., Davidson, J., Wilson, J., Waldrop, T. 2009. Advances in Fish Harvest Technologies for Circular Tanks. Aquacultural Engineering. 40(2):62-71. Interpretive Summary: Fish transfer and grading technologies for large circular tanks were evaluated for their labor-saving potential and fish survival, as well as to demonstrate the technology required to enable dramatic increases in domestic commercial fish production. A clam-shell type crowder/grader system used with an air-lift fish pump or with a culture tank sidewall drain box (both incorporating a dewatering/sorting chamber) were found to reduce labor when grading and harvesting large circular culture tanks. Only 1 worker was required at the sorting box to selectively grade and harvest a 150 m3 circular culture tank. With these selective harvest technologies, the majority of the fish in the culture tank were never lifted from the water during the self-sorting process, which minimized stress, perhaps enhancing final product quality. In contrast, harvesting the tank using the purse seine and hand brailing was much more labor intensive and increased the stress on the fish, as indicated by a nearly 10-fold increase in fish mortality compared to the mortality observed when the clam-shell type crowder/grader system and an air-lift fish pump or sidewall drain box were used during fish harvest. In addition, a non-invasive technique that takes advantage of the fish's carbon dioxide avoidance response was developed to passively encourage fish to congregate in a distinct location where they could be readily pumped to another location, or to voluntarily swim into a separate tank. Application of these new processes can provide a more efficient, inexpensive, safe, and reduced stress process for transferring fish from large and deep circular culture tanks. This work, together with technologies being developed by industry, could significantly improve production efficiency in land-based fish farms, and pave the way for major expansions in overall production.
Technical Abstract: Improved equipment and husbandry practices are required to effectively grade and harvest fish in large land-based culture tanks. The objective of our work was to develop and evaluate several types of relatively inexpensive, portable, and efficient fish handling equipment to reduce the labor requirement for grading and harvesting fish from large circular culture tanks. This equipment and husbandry practices also had to provide for worker safety and minimize the stress or damage to the fish. Two techniques were developed and evaluated to remove the entire population from a large and deep circular tank, i.e., (a) purse seine and (b) carbon dioxide avoidance response. Two other techniques were developed and evaluated to remove the fish from a culture tank after they had been top-graded in situ using a 3-panel clam-shell grader: (c) an airlift fish pump and hand sorting/dewatering box and (d) a sidewall drain box for hand sorting/dewatering. Some of these technologies are brand new, while others (such as the purse seine) have been used in other applications. Our commercial-scale evaluation of these technologies provided insight into the advantages and disadvantages of each option. Use of the carbon dioxide avoidance response can be effectively used, with little labor input and practically zero mortality to non-selectively remove the entire fish population from a fish culture tank. The combination of the clam-shell crowder with the sidewall drain harvest box was our preferred harvest method, especially when top-grading the population was required, primarily due to its low labor requirement, low fish mortality, and rapid harvest rate. Ultimately, the more effective technologies and practices should help fish farmers overcome scale-up issues and improve land-based fish farm production per unit investment.