Bacterial coldwater disease and other infections caused by Flavobacterium psychrophilum are a worldwide concern, particularly for freshwater salmonid hatcheries. F. psychrophilum infections can be difficult to control; antibiotic resistance is common and no effective vaccines are currently available. This review summarizes the biology and characteristics of this important pathogen, as well as the techniques required for isolation and identification. In addition, the epidemiology, clinical signs, treatment, and possible preventative measures of bacterial coldwater disease are discussed.

While structural complexity has been used extensively during hatchery rearing in an attempt to improve poststocking survival, the potential impact of this complexity on hatchery rearing performance has largely been ignored. This study examined the growth and condition of juvenile Rainbow Trout Oncorhynchus mykiss reared in nearly fully covered circular tanks containing nine vertically oriented round aluminum rods (structurally complex) compared with that of trout reared in almost fully covered tanks with no rods (control) at two water velocities (2.0 body length (BL)/s and 2.75 BL/s). After 51 days, total tank weight gain was significantly higher in the structurally complex tanks than in the control tanks, regardless of water velocity. The feed conversion ratio was also significantly better in the structurally complex tanks [mean (SD) 1.25 (0.10)] than in the control tanks [1.66 (0.41)]. There were no significant differences in hepatosomatic index, splenosomatic index, and viscerosomatic index between the fish from the structurally complex and the control tanks. Total tank weight gain was significantly higher and the feed conversion ratio significantly lower in the lower water velocity tanks than in the higher water velocity tanks. These results indicate that vertically oriented aluminum rods can be used to increase structural complexity and improve Rainbow Trout rearing performance in circular rearing tanks, with minimal effects on regular tank cleaning.

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This study evaluated the effectiveness of two different environmental enrichment structures on the growth and condition of juvenile Rainbow Trout Oncorhynchus mykiss. Fish were reared in covered tanks with vertically suspended linear or spherical structures. Spherical structures were comprised of seven colored plastic balls that were vertically stacked and suspended on a string from the overhead tank covers, while linear structures consisted of vertically oriented aluminum rods. In the tanks with either of the environmental enrichment treatments, weight gain and feed conversion ratio were significantly improved relative to control tanks. Weight gain and feed conversion ratio were also significantly improved with the use of spherical structures compared to the use of linear structures. To provide substantial benefits during the rearing of Rainbow Trout in circular tanks, the use of vertically suspended spherical structures is recommended.

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