Rearing in enriched hatchery tanks improves dorsal fin quality of juvenile steelhead

The present study compared the dorsal fin Condition of juvenile steelhead Oncorhynchus mykiss reared in conventional hatchery tanks, enriched hatchery tanks (i.e., with the addition of submerged structure, overhead cover, and underwater feeders), and a natural stream to determine whether structural enrichment would reduce dorsal fin erosion in hatchery-reared fish. Dorsal fin height at 27 d postemergence did not differ significantly between the two hatchery rearing treatments. Steelhead reared in the conventional tanks had dorsal fins 78% as long as steelhead reared in enriched tanks and in the natural stream at 50 d postemergence (P < 0.05) and 45-55% as long at 64 d posternergence (P < 0.05). Variation in fin length did not substantially affect the ability to achieve dominance in agonistic contests for feeding territories; fish with longer dorsal fins won approximately 57% of contests against fish with fins that were 25% shorter on average. Rearing methods (such as structural enrichment), that simultaneously improve several attributes of juvenile salmonid morphology, physiology, or behavior may be important in the development of conservation hatchery rearing strategies.