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below the dorsal fin, and on the caudal peduncle. Juvenile bluegill lost elastomer marks applied to the dorsal surface of the skull but retained all other marks. Bonneau et al. (1995) reported elastomer retention of nearly 100% after 4 months for implants in juvenile and adult salmonids on the top of the head, adipose tissue behind the eye, adipose fin, dorsalfm, pectoral fin, and caudal fin. During the course of our study, razorback sucker mortality averaged 12%. The mortality was spread among fish of all groups and apparently unrelated to marking (Table 3). Colorado squawfish suffered heavy mortality (79%) between 11 July and 16 September, the result of bacterial septicemia. The mortality was also spread among fish of all groups and apparently unrelated to marking (Table 5). Our experience was that between 130 and 140 fish per h could be marked by one person implanting elastomer at two locations on each fish and one person anesthetizing and handling fish. Approximately three times that number can be freeze-branded per h by a single individual. Conclusions 1. Freeze branding had excellent retention for 15 months for both razorback sucker and Colorado squawfish. 2. Elastomer recognition, although acceptable for short time periods (red and orange) on Colorado squawfish, were not suitable for marking fishes if identification is desired beyond 12 months. 3. One person implanting elastomer at two locations on each fish and one person anesthetizing and handling fish can mark 130-140 fish per h. Approximately three times that number can be freeze- branded per h. 15