This abstract summarizes the information obtained from the first 2 years of a study to produce 0-age smolts in the Carson Hatchery stock reared at Leavenworth National Fish Hatchery. Production of 0-age smolts is being investigated as a potential means to improve production of spring chinook in the mid-Columbia region. Disease, passage, and other undefined problems are currently limiting hatchery production through poor return rates in the range of 0.001 to 0.007 adults per smolt.

The studies are conducted under the mid-Columbia Coordinating Committee with the cooperation and support of the U.S. Fish and Wildlife Service and the Washington Department of Fisheries. Under the Coordinating Committee, the studies have been restricted to using only accelerated rearing as a means of producing 0-age smolts. Accelerated maturation in brood stock was not permitted because of concerns by some members that this procedure might result in adverse genetic changes.

The first objective of these studies is to determine if 0-age smolts can be produced. Second, we are attempting to determine if there is an advantage to producing 0-age smolts in this region with this stock. We have just completed the second year of this study. We have reared and assessed the smoltification of two year classes of 0-age spring chinook. However, we do not yet have any adult return data to complete our evaluation.

Our method of producing 0-age smolts was to take the first embryos available at the Leavenworth Hatchery and incubate these embryos and rear the young under the warmest water conditions we could provide. Eggs taken from the first and second spawnings in mid-August were fertilized with a single male for each female and incubated separately for each female until IHN test results were available. Embryos from IHN-positive fish were then incubated separately from those of IHN-negative parents. In 1987, all embryos were incubated at Leavenworth; however, in 1988, about 125,000 IHN-free embryos were transferred to Wells Hatchery for rearing in warmer water.

At Leavenworth, the incubation and early rearing water temperature was raised about 2-3°C above the well-water temperature used for normal production fish. A swimming pool heater heated the Leavenworth well water to provide temperatures of about 12°C. The group of eggs taken to Wells Hatchery in 1989 were incubated in warm well-water of about 12-14°C.

Prior to release, the Wells groups were returned to Leavenworth for a 2-week holding period. This was to ensure that all spring chinook test fish returned to the Leavenworth Hatchery. In 1988, the Wells group was held in a modified fish ladder. High water and debris in Icicle Creek allowed some of these fish to escape after only 2 days holding.

All fish in this study were marked with a freeze brand and coded-wire tagged. Tagging and branding of the individual groups was conducted in March to give the fish adequate time to recover from any marking stress prior to release.

Physiological monitoring of each group was conducted to detect changes in plasma thyroxine (T₄) and gill ATPase levels. Beginning in early March, samples of 10 fish were collected each week from each group for this monitoring. Growth was measured by taking weight and length measurements from each of these samples.

Following release, the migration rates of each group were monitored at several downstream locations. Smolt sampling activities at Rock Island, Priest Rapids, and McNary Dams collected these groups during their migration through the Columbia River reservoirs.

Samples of about 1,100 fish from each group were retained at release for saltwater survival testing. These fish were transferred to Manchester, Washington, on Puget Sound where they were placed in net-pens at the National Marine Fisheries Service facility. The fish were placed in a freshwater lens held in place by a vinyl skirt around the top of the pew. An initial sample of 100 fish and all mortalities were collected for disease analysis.

This study is in progress and has not produced final results. Results available include information on rearing and migration of juveniles. No adults have yet returned.

As anticipated, the growth of juvenile spring chinook at Leavenworth was increased considerably by raising the water temperature during their first winter. Fish hatched in late September and emerged in late October. The size (weight) of these fish remained about twice that of fish from the normal hatchery production as shown by the 1987 data (Fig. 1). The 1988 fish showed similar growth rates.

By the April release dates, the accelerated fish had reached sizes apparently capable of beginning migration. Accelerated fish reared at Leavenworth were about 8 g while fish reared in part at Wells in warmer water had reached about 16 g by late April. Similar growth rates were produced in 1988-89, when both embryos and fry were transferred to Wells for rearing.

Physiological monitoring showed that the accelerated fish were producing peaks in T₄ and ATPase levels that indicate smolting or readiness to smolt. This response was greatest in the Wells group. The peaks in T₄ were generally lower in accelerated fish than in yearling or normal production 0-age fish at Leavenworth.

Use of a longer photoperiod in a small group of Leavenworth accelerated fish in 1989 showed a greater T₄ peak comparable to normal production fish. The ATPase levels in all accelerated groups tended to be nearly the same as or slightly higher than yearling or normal production fish.

Migration rates of accelerated groups were initially very rapid but decreased markedly downstream from the first recovery location. Accelerated fish appeared at Rock Island Dam in large numbers within 2-3 days of release. Accelerated fish tended to be collected in higher numbers than yearlings at Rock Island Dam. This differential recovery appears to be a unique characteristic of the dam rather than an indication of survival. However, at Priest Rapids and McNary Dams, yearlings were recovered at much higher rates than the accelerated fish.

Travel times to Rock Island Dam (Fig. 2) were longer, on the average, for accelerated groups than for yearlings, although initial portions of each accelerated group matched the rapid yearling migration to this rust dam. At Priest Rapids and McNary Dams, the migration rates of accelerated groups were much lower than the yearling rates. At McNary Dam, few 0-age fish were recovered until early June, while nearly all yearlings passed the dam in May (Fig. 3).

Saltwater survival was initially high for both years. This indicates that the physiological condition of the accelerated groups allowed them to adapt to seawater. All fish had moved from the freshwater lens into the deeper seawater layer after several days. Mortality rates were high (46-80%) in accelerated groups during the first 120 days of saltwater rearing. Those deaths were due to vibriosis and BKD during 1987. In 1988, the fish were vaccinated against vibrio and had low mortality rates (0.3-3.6%) for the first 30 days. Later, mortality rates due to BKD were much higher.

Future adult recoveries will provide a complete evaluation of this study.

Figure 1. Growth curves of the accelerated 0-age groups (Take 1, Take 2, and Wells) and the normal 0-age Leavenworth group that was spawned on the same day as Take 2.

Figure 2. Daily brand recoveries of Take 1, Take 2, Wells, and Leavenworth yearling groups at Rock Island Dam expressed as percentages of the total number of each brand recovered for the season (shaded area).

Figure 3. Daily brand recoveries of Take 1, Take 2, Wells, and Leavenworth yearling groups at McNary Dam expressed as percentages of the total number of each brand recovered for the season (shaded area).

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