|GOOD, CHRISTOPHER - Freshwater Institute|
|DAVIDSON, JOHN - Freshwater Institute|
|WELCH, CARLA - Freshwater Institute|
|SNEKVIK, KEVIN - Washington State University|
|SUMMERFELT, STEVEN - Freshwater Institute|
Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2011
Publication Date: 5/1/2011
Citation: Good, C., Davidson, J., Welch, C., Snekvik, K., Summerfelt, S. 2011. The effects of ozonation on performance, health and welfare of rainbow trout Oncorhynchus mykiss in low-exchange water recirculation aquaculture systems. Aquacultural Engineering. 44:97–102. DOI: 10.1016/j.aquaeng.2011.04.003.
Interpretive Summary: Ozone is used in modern aquaculture facilities to improve water quality by reacting with organic and inorganic impurities. In this way, ozone is useful in improving water quality in water recirculation aquaculture systems (WRAS), particularly when these systems are operated with very low water exchange. The effects of ozone on the health and welfare of fish raised in WRAS, however, needed to be examined to determine whether this water treatment technology is detrimental to overall fish health and welfare. A controlled four-month experiment was carried out at The Freshwater Institute using 6 WRAS (3 with ozonation, and 3 without) stocked with rainbow trout that were grown under these conditions from ~300g to market size. By study's end, fish in the ozonated WRAS weighed significantly more than the non-ozonated fish cohort. Numerous fish health outcomes were examined, including histopathology, blood gas and chemistry, and fin condition. Although minor subclinical differences were noted in several of these areas, no major differences in the health and welfare of fish were determined between the two treatment groups. Our results demonstrate that ozone can be used in low exchange WRAS to improve fish performance without significantly affecting fish health and welfare.
Technical Abstract: A controlled four-month trial was conducted to compare the effects of ozonation (oxidation-reduction potential setpoint = 250 mV) versus no ozonation on rainbow trout Oncorhynchus mykiss performance, health, and welfare in replicated WRAS operated at low exchange rates (0.26% of the total recirculating flow) and high feed loadings (3.9 kg/day per cubic meter/day makeup flow). Rainbow trout at 74 +/- 2g (mean +/- standard error) in size were randomly stocked into six replicated 9.5 cubic meter WRAS (1000 fish per system). Ozonation of the three treatment WRAS began two months post-stocking following biofilter acclimation when fish were 295 +/- 1g. Fish were maintained at densities between 40 kg/cubic meter and 80 kg/cubic meter throughout the study at water temperatures of approximately 13-17 degrees C. By study's end, percentage survival for both groups was high (>98%). Fish in ozonated systems weighed significantly (p<0.05) more at study's end than fish from the non-ozonated systems (1161 +/- 6g vs. 993 +/- 12g, respectively). Histopathological evaluation revealed increased levels of gill epithelial hyperplasia and hypertrophy, as well as hepatic lipidosis, in fish from ozonated systems; however, all lesions were subclinical. Fin condition was good overall in both groups, although fish from non-ozonated WRAS had better (p<0.05) dorsal fin indices than fish in the ozonated cohort. The major blood chemistry finding was higher (p<0.05) urea nitrogen in fish from non-ozonated systems (15.33 +/- 0.90 mg/dL, vs. 6.800 +/- 0.470 mg/dL in fish from ozonated WRAS). Overall, the results of this study indicate that raising rainbow trout to market size in ozonated WRAS improves fish performance without significantly impacting their health and welfare.