Early Rearing of Cutthroat Trout Technical Report WESTERN REGIONAL AQUACULTURE CENTER Compiled by Gary Fornshell, University of Idaho Extension Christopher Myrick, Colorado State University United States Department of Agriculture National Institute of Food and Agriculture 1 2 PROJECT PARTICIPANTS Christopher Myrick, Colorado State University Mandi Brandt, Colorado State University Rick Barrows, US Department of Agriculture Ken Cline, Cline Trout Farms Gary Fornshell, University of Idaho Extension Greg Kindschi, US Fish and Wildlife Service Molly Webb, US Fish and Wildlife Service Kevin Kappenman, US Fish and Wildlife Service Jeremy Liley, Liley Fisheries, Inc. Photo credits: Cover: Dec Hogan/iStock/Thinkstock Above: U.S. Geological Survey/photo by Jonny Armstrong 3i TABLE OF CONTENTS Background 1 Native Cutthroat 2 Early Rearing Research 5 Optimizing Feed 5 Research Findings and Recommendations 5 Supplementing Live Artemia 6 Water Temperature 7 Rearing Density 8 Temperature Test Results 8 Rearing Density Test Results 10 Production Scale Trial 10 Cost-Benefit Matrix 11 Summary 11 Suggested Readings 12 Acknowledgments inside back cover 4ii FIGURES 1. Map showing the distribution of extant cutthroat trout subspecies in the western United States 4 2. Comparison of the effects of diet on the coloration of juvenile Colorado River cutthroat trout 7 3. A small-scale Artemia hatching system 8 4A. Effects of water temperature on the final wet weights of juvenile Snake River cutthroat trout 9 4B. Effects of water temperature on the final wet weights of juvenile Yelllowstone cutthroat trout 9 5A. Final wet weights of Colorado River cutthroat trout fed the regular Trout Co. #1 + Artermia 9 5B. Final wet weights of Colorado River cutthroat trout fed the Premium Trout Co. #3 + Artemia 9 TABLES 1. Primary state agency responsible for regulating aquaculture in the western United States 1 2. Protein and fat percentages of the feeds used in the cuttthroat trout early rearing study 5 3. Feeds used in the supplemental feeding trial with juvenile Snake River cutthroat trout 5 4. Final wet weights for Snake River, Yellowstone, and Colorado River cutthroat trout fed on a variety of commercially available or open-formula diets 6 5. Effects of rearing density on the growth of first-feeding Colorado River cutthroat trout 10 6. Cost-benefit matrix for Colorado River cutthroat fed one of three diet combinations 12 7. Cost-benefit matrix for Snake River cutthroat fed one of two diets 12 iii5 6 BACkgROUND The charm of fishing is that it is the pursuit of what is elusive but attainable, a perpetual series “ of occasions for hope. —John Buchan ” Cutthroat trout (Oncorhynchus clarkii) are popular game species are allowed for propagation. Table 1 below lists the fish in the western United States. For private fish farmers, state agency responsible for regulating aquaculture in each they represent a potential high-value fish for profitable rec- of the western states. State aquaculture coordinators can reation-based aquaculture. Cutthroat trout are potentially provide information about aquaculture regulations. For more valuable for the recreational market than the more a directory of state coordinators, go to the National common rainbow trout (Oncorhynchus mykiss) because Association of State Aquaculture Coordinators website they are in limited supply and are considered by some to (http://www.nasac.net/). Alternately, you can contact your be more aesthetically pleasing. County Extension Office for assistance. Propagation of cutthroat trout in public hatcheries is The Western Regional Aquaculture Center (WRAC) also necessary for conservation and restoration programs. recently completed a study on the economic contributions They are primarily produced for put-and-grow fisheries, thus placing a premium on high rates of fry and juvenile Table 1. Primary state agency responsible for regulating survival, and good fry quality (i.e., intact fins and oper- aquaculture* in the western United States. cula). However, insufficient knowledge of the optimal early rearing culture requirements has led fish culturists to use STATE DEPARTMENT conditions similar to those for rainbow trout with variable success. Arizona Department of Agriculture Lack of specific feeds for cutthroat trout is one factor California Department of Fish and Game that contributes to inconsistent and non-repeatable Colorado Department of Agriculture growth, survival, and quality from year to year. Two other critical factors that substantially influence fish perfor- Idaho Department of Agriculture mance are rearing temperature and rearing densities. Montana Department of Fish, Wildlife, and Parks Optimizing early rearing by focusing on feed, water tem- Nevada Department of Wildlife perature, and rearing density should result in improved New Mexico Department of Game and Fish growth, quality, and survival. Ultimately, fish culturists Oregon Department of Fish and Wildlife that optimize early rearing conditions for cutthroat trout will produce a fish desired by both customers of the Utah Department of Agriculture private recreation-based aquaculture sector and the public Washington Department of Fish and Wildlife hatcheries engaged in conservation and restoration efforts. Wyoming Department of Game and Fish Aquaculture producers of recreational fish are located * Some states have two departments co-regulate aquaculture throughout the western states with the majority in Cali- where one department may issue a fish propagation license fornia, Colorado, Oregon, and Washington. State regula- and another department regulates species allowed and impor- tions for private aquaculture production vary, including tation requirements. which state departments regulate aquaculture and which 1 of the private, recreation-based aquaculture industry in • Cutthroat trout are generally spring spawners, a trait the western United States (depts.washington.edu/wracuw/ that can increase the likelihood of hybridization (inter- research/starter-diets_trout.html). Western suppliers of breeding) with the closely related rainbow trout. recreational fish generate annual sales of $57.2 million and • Their natural diet consists primarily of insects (both 1237 jobs. The total annual economic contribution of this aquatic and terrestrial) and other aquatic invertebrates, important aquaculture sector in the West is $108.2 mil- though larger fish will also start to feed on other fish. lion. A variety of cold-, cool-, and warm-water species are • Because they are very closely related to rainbow trout, sold to recreational outlets, to brokers, as food fish, and to cutthroat trout readily interbreed to produce cuttbows, other markets. The majority of salmonids (88%) are sold a hybrid cross that can sometimes breed on its own. to public and private recreational outlets, such as private This propensity to hybridize with rainbow trout is fisheries, fishing clubs, municipalities, and home owner one of the reasons cutthroat trout subspecies declined associations. Only a small percentage of salmonids are throughout their range—as rainbow trout were intro- sold to brokerages. Almost all salmonids produced in the duced, the pure lines of cutthroat trout hybridized and western region are sold within the western states. declined in fitness, range, and abundance. • Like all trout and salmon, they build redds, typically NATIVE CUTTHROAT TROUT in the gravel of streams, rivers, or the inlets and outlets The western United States was home to a variety of of ponds and lakes. Egg incubation times vary with cutthroat trout (O. clarkii), including at least 11 distinct water temperature. subspecies or strains of which approximately 9 were still • All cutthroat trout are excellent sportfish, responding extant in 1992 (Figure 1). Historical distribution of cut- favorably to flies, lures, and bait. They are often prized throat trout subspecies included temperate rainforests by anglers for their coloration and vigorous fighting of the Pacific Northwest, pluvial basins within the Great abilities. Basin, subalpine areas of the Rocky Mountains, and high deserts of the Southwest. These fish, while closely related The focus of this paper is on the optimization of early to rainbow trout (O. mykiss), were found primarily in rearing techniques for three subspecies of cutthroat trout: inland drainages, while the strongholds of rainbow trout the Colorado River cutthroat trout (O. c. pleuriticus), the were the coastal drainages. The inland cutthroat trout Yellowstone cutthroat trout (O. c. bouvieri), and the Snake were able to take advantage of a diverse range of habitats River cutthroat trout (O. c.). These subspecies were chosen and occurred in everything from tiny headwater streams for a variety of reasons, including their availability in to large rivers and very large lakes (e.g., Lake Tahoe on large enough numbers to permit controlled laboratory the California–Nevada border). studies, their relationships to other cutthroat trout (e.g., Not surprisingly, this diverse group of habitats also the Colorado River cutthroat trout is closely related to led to a diverse set of life history strategies, with some the greenback cutthroat, O. c. stomias, and Rio Grande fish acting much like anadromous salmon, living in large cutthroat trout, O. c. virginalis), and the growing demand lakes and migrating into rivers to spawn, while others were from fish culturists for information on these species. resident in rivers and streams year-round. In terms of size, The Colorado River cutthroat trout