Proceedings of the 56 Annual Northwest Fish Culture Conference

Two facilities, Pahsimeroi Hatchery and Sawtooth Hatchery, operated by the Idaho Department of Fish and Game remain positive for Myxobolus cerebralis. Both facilities rely on river water supplies to complete rearing of ESA-listed Chinook salmon to the smolt stage prior to release. We have previously reported the seasonal pattern of infectivity to rainbow trout sentinels exposed to these waters. Progress in reducing the exposure of cultured Chinook has been provided at Pahsimeroi Hatchery by Idaho Power Company through facility improvements and expansion of the well water supply. Restoration of the ground water supply volume for Sawtooth Hatchery has begun by LSRCP as the most cost effective method of expanding early rearing capabilities for Sawtooth Hatchery to avoid exposure to the parasite and other pathogens as well. We felt that determining the extent of M. cerebralis infectivity within the Salmon River water supply of Sawtooth Hatchery would assist these efforts. The portion of the Salmon River upstream of Sawtooth Hatchery includes the terminus of the entire drainage, the longest free-flowing river system in the continental United States. The upland area within the Sawtooth Valley is within federal ownership while the river bottoms are privately held. Glaciation was extensive in the Sawtooth Range resulting in extensive gravel deposits and spring water that emerges at the valley floor. Three trials with sentinel rainbow trout were performed in 2004 and 2005 to determine the distribution of M. cerebralis infectivity in the Salmon River upstream of Sawtooth Hatchery. The first trial was conducted during May at a time our previous projects demonstrated a high probability of infection. Exposure sites were selected to reveal the overall pattern of M. cerebralis infectivity throughout the drainage. Results of the first trial illustrated that infection was not present in Alturas Lake Creek, Camp Creek, Frenchman Creek, or Smiley Creek which join to form the Salmon River. There were, however, two areas in the Salmon River where infections seemed to originate: downstream of the confluence of Camp, Frenchman, and Smiley creeks and also in the main stem Salmon River in the vicinity of Obsidian, ID. In general, the prevalence of infection was high in the areas where sentinels became infected; the intensity as measured by spore counts was low compared to sentinel trials conducted in the Pahsimeroi River and Lemhi River. The second sentinel trial was designed to examine locations on Pole Creek, Beaver Creek, and the upper Salmon River to further define the source of M. cerebralis. Both Pole Creek at its confluence and the Salmon River (a small creek at this area) are sites where the infection originates. The third sentinel trial demonstrated that the previously-identified sources could be replicated during the spring as well as the fall months. The same pattern of increasing prevalence was obtained from the sites on Pole Creek. Therefore, the source of the parasite in the river supply of Sawtooth Hatchery is about 18 river miles upstream in the Salmon River. Management implications of this study indicate that this infection was independent of sockeye salmon recovery efforts in Alturas and Pettit lakes. The origin of the infection in the Salmon River may have resulted from the stocking of infected fish from a private hatchery or the IDFG Hayspur Hatchery when it was positive. Our laboratory has routinely detected M. cerebralis at Sawtooth Hatchery since 1987. Integrated Management of BKD Using ELISA-based Culling Doug Munson*, Idaho Department of Fish and Game, Eagle Fish Health Lab, Eagle, ID 83616. Phone: 208-939-2413. Fax: 208-939-2415. Email: [email protected] Abstract The Idaho Department of Fish and Game (IDFG) Chinook salmon program has a history of managing Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), dating back to 1969 at Rapid River Hatchery and 1980 for McCall Hatchery. The chronological events described in annual and brood year reports from these facilities document the progression of events that led IDFG into developing an integrated BKD management program for hatchery reared Chinook salmon. The cornerstone of this management strategy was use of the enzyme linked immuno-sorbent assay (ELISA) based culling of eggs from females with high optical density values for Renibacterium. The success of this program has been documented by mortality records, routine inspection, and diagnostic sampling during the 18 month period of hatchery rearing.The Idaho Department of Fish and Game (IDFG) Chinook salmon program has a history of managing Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), dating back to 1969 at Rapid River Hatchery and 1980 for McCall Hatchery. The chronological events described in annual and brood year reports from these facilities document the progression of events that led IDFG into developing an integrated BKD management program for hatchery reared Chinook salmon. The cornerstone of this management strategy was use of the enzyme linked immuno-sorbent assay (ELISA) based culling of eggs from females with high optical density values for Renibacterium. The success of this program has been documented by mortality records, routine inspection, and diagnostic sampling during the 18 month period of hatchery rearing. Early attempts to control this disease were limited to injection of erythromycin for returning adult salmon and erythromycin medicated feed treatments after clinical signs had been observed. Fertilized eggs were water hardened in 1 mg/l erythromycin. Prophylactic feeding of erythromycin medicated feed began in 1977 in the juvenile salmon at Rapid River Hatchery. The treatments became a standard operating procedure for rearing Chinook salmon at Idaho Department of Fish and Game facilities in 1984. An integrated program of treating hatchery reared salmon for BKD at each life stage was implemented in 1993. This program consists of the following: (1) 20 mg/kg intra-peritoneal injection of erythromycin to returning adult salmon; (2) iodophor disinfection of fertilized eggs in 100 mg/l iodine for 30 minutes during water hardening; (3) testing of kidney tissue from all spawned females by ELISA. To limit risk of vertical transmission and subsequent horizontal transmission, the eggs from brood females with ELISA optical densities of 0.25 or greater were usually culled. In years with low adult numbers, a high BKD segregation group consisting of progeny of females with ELISA optical densities of 0.25 to 0.6 has been reared in isolation. This has been considered the high BKD segregation group since 1998; and (4) usually each brood year receives two prophylactic regimens of erythromycin feed. The high BKD segregation group received an additional erythromycin medicated feed application. Pre-spawning mortality of Chinook salmon adults due to BKD averaged 37.3% before the implementation of the strategy described above. Average pre-spawning mortality has decreased to an average of 5% per year, since the implementation of this integrated strategy. The IDFG Chinook salmon hatchery program has not experienced an epizootic due to BKD since 1993. Although clinical signs of BKD have been noticed after stressful events, minor outbreaks have been controlled with medicated feed. Cumulative mortality from ponding to release, from all causes, has decreased from an average of 4.2% to 0.6% per year at Rapid River, and an average of 6.8% to 1.7% per year at McCall, since implementation of this strategy. This strategy has been instrumental in reducing the risk of vertical and horizontal transmission of BKD in the hatchery and subsequently to wild/natural stocks after release. We recommend implementation of this BKD management strategy if the salmon hatchery program is considered risk intolerant. Environmental Risk Assessment for Application of Erythromycin to Control Bacterial Kidney Disease in Salmon Christine M. Moffitt*, Idaho Cooperative Fish and Wildlife Research Unit, University of Idaho, Moscow ID 83844-1136. Phone: (208) 885-7047. Fax: (208) 885-9080. Email: [email protected] Abstract Erythromycin is effective as a therapeutant to control bacterial kidney disease in salmonids. FDA requires an environmental risk assessment to assess the proposed therapy. Use patterns for seven years in Idaho, Washington and Oregon were examined using records of use. FDA’s worst case scenario was developed assuming all the day’s treatment was applied directly into the water and released over a24 h. Using this scenario, the average discharge from all hatcheries in Washington and Oregon was less than 10 μg/L. Average discharges in Idaho were variable. In a few cases the worst case scenario produced effluents that might be considered toxic to some algae.Erythromycin is effective as a therapeutant to control bacterial kidney disease in salmonids. FDA requires an environmental risk assessment to assess the proposed therapy. Use patterns for seven years in Idaho, Washington and Oregon were examined using records of use. FDA’s worst case scenario was developed assuming all the day’s treatment was applied directly into the water and released over a24 h. Using this scenario, the average discharge from all hatcheries in Washington and Oregon was less than 10 μg/L. Average discharges in Idaho were variable. In a few cases the worst case scenario produced effluents that might be considered toxic to some algae. Intermittent feeding for controlling steelhead growth at Hagerman NFH Hagerman Hatchery Evaluation Team; Nathan Wiese*, Hagerman National Fish Hatchery, 3059-D NFH Rd, Hagerman, ID 83332. Phone: 208-837-4896. Fax: 208837-6225. Email: [email protected] Abstract As part of the Lower Snake River Compensation Plan, Hagerman National Fish Hatchery releases steelhead at 180 -250 mm according to NOAAFisheries guidelines designed to reduce competition and predation on native salmon. Steelhead are reared at 59 F that requires reduced feeding to meet target size. Experimental groups were fed for 15 days and then fasted 15 days during brood years 1996-99 to determine if intermittent feeding would reduce growth effectively. Intermittently-fed steelhead performed as well asAs part of the Lower Snake River Compensation Plan, Hagerman National Fish Hatchery releases steelhead at 180 -250 mm according to NOAAFisheries guidelines designed to reduce competition and predation on native salmon. Steelhead are reared at 59 F that requires reduced feeding to meet target size. Experimental groups were fed for 15 days and then fasted 15 days during brood years 1996-99 to determine if intermittent feeding would reduce growth effectively. Intermittently-fed steelhead performed as well as continuously-fed steelhead based on returns and fish health parameters. Hagerman NFH has adopted a modified intermittent feeding approach that reduces steelhead growth. Heat Induced Triploid Trout Production Brad Dredge*, Idaho Department of Fish and Game, Hayspur Fish Hatchery, 071 US Highway 20, Bellevue, ID 83313. Phone: 208-788-2847. Fax: Email: [email protected]