Freeze Brands and Submandibular Latex Injections as Identifying Marks on Rainbow Trout

Abstract
The percent retention of freeze brands and blue and red latex injections on 5,080 rainbow trout (Salmo gairdneri) was evaluated in a hatchery and in a stocked stream. Freeze brand retention was 98% after 13.5 weeks in the hatchery. In the stream, retention was 96% at 13.5 weeks and 92% at 22 weeks. Blue submandibular latex injections were retained at 92% after 13.5 weeks in the hatchery. Red latex injections, however, were consistently inferior (75% at 13.5 weeks) both to the blue latex and freeze brands. Fish examined in creel surveys (used to recover marked fish from fished streams) contained an average of 10% decapitated fish; thus, injections were missing. The brands were recognizable, however, even when fish were scaled. Our stainless steel branding symbol produced fewer high quality marks than silver branding symbols used in other marking studies.

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