Bacterial outbreak closes three DFW hatcheries, over 60,000 trout have died at Mojave Narrows – ONS – Matthews – 03 July 2020

Department of Fish and Wildlife photo of its Mojave River Hatchery.

Bacterial outbreak closes three DFW hatcheries, over 60,000 trout have died at Mojave Narrows – ONS – Matthews – 03 July 2020

Bacterial outbreak closes three DFW hatcheries, over 60,000 trout have died at Mojave Narrows – 03 July 2020 Compiled by Jim Matthews

A bacterial outbreak at the Mojave River Hatchery in Victorville has already killed 60,000 of the 650,000 trout at this Department of Fish and Wildlife facility, according to Jay Rowan, the environmental program manager with the DFW’s hatchery program in Sacramento. Two other DFW hatchery facilities in Inyo County have also tested positive for the deadly bacteria, but they have not experienced any fish losses.

Jess Ranch, a private hatchery facility near Mojave River Hatchery in Victorville, has also tested positive for the virus but has also experience few losses.

Rowan said the outbreak has led to the immediate cessation of trout plants from these four hatcheries, including Jess Ranch, until the fish no longer test positive for the virus.

“The biggest problem is this bacteria is not out in the wild, and we can not plant these fish,” said Rowan. He said Jess Ranch hatchery managers have voluntarily agreed to not plant fish until the problem is remedied.

This means that there will be no DFW or Jess Ranch plants throughout Southern California, and that is expected to continue for at least the foreseeable future. This means the end of nearly all trout plants in Ventura, Santa Barbara, Los Angeles, San Bernardino, Riverside, San Diego, and Imperial counties through at least the rest of the summer. There will also be a reduction of plants in Inyo and Mono counties because both the Black Rock and Fish Springs hatcheries in Inyo County have also tested positive for the bacteria, but the Hot Creek hatchery remains negative for the bacteria and trout will continue to be planted from this facility.

The bacterium – Lactococcus garvieae – is a new bug in trout hatcheries, not found before 1950 and then only in the Far East infecting rainbow trout, yellowtail, and grey mullet in both hatchery and marine hatchery settings. It wasn’t until 1988 that it appeared outside of this region when it appeared in a European trout hatchery. It has since spread slowly, but this is the first outbreak in California.

While little is known about the bacterium, it is similar to streptococcus and infected fish show symptoms that including bulging eyes, lethargic or erratic swimming, and eventually death. Some fish carrying the bacteria may be asymptomatic, assisting spread. Out of caution and not wanting to spread the bacteria to wild populations, the DFW has ceased all plants from infected hatcheries until more is learned about its mortality and prevalence. Testing is ongoing at all other DFW hatchery facilities, but none have tested positive so far.

There is only one treatment for the bacteria in large hatchery settings, and Rowan said it has been ineffective at the Mojave River Hatchery, but it has worked fairly well at the privately-owned Jess Ranch hatchery.

“Our only option is not working well on the bacteria [at Mojave]. We’ve been treating for some time now, but 60,000 trout have died so far despite the treatments. The death rate just keeps going up, up, up,” said Rowan.

Dieoffs in Black Rock and Fish Springs have not been observed, and Rowan said this was because it is believed the bacteria become more virulent as water temperatures warm. In recent weeks, the water temperature at Mojave River has increased into the low 60s, while the Sierra hatcheries still have water temperatures in the mid-50s.

“We don’t have tried-and-true strategies on hand to combat it,” said Rowan. “A successful approach would have three components: Treating the affected fish at the hatcheries, finding the origin of the outbreak, and planning ahead to contain and prevent the spread of the bacteria.

“Unfortunately, we may be in for a long battle here, which means there will not be a lot of fish plants in the near future in the eastern Sierra and Southern California. I wish we could give anglers a target date for when we think we can start planting again, especially since our one treatment option does not appear to be working very well right now,” said Rowan.

Southern California’s other hatchery, the Fillmore Hatchery, is just now coming back on line after water problems and maintenance for over a year. It was just starting to receive fish for fall and winter plants at the three major state water project reservoirs in Southern California – Castaic, Pyramid, and Silverwood. The trout in this facility were sampled late this past week and results on those tests will not be known until late this week.

The DFW has not put a value on the losses of trout to this point because the losses have been across all age groups of fish at Mojave River, and this is just the early stages of the outbreak. Rowan said that the DFW routinely uses the figure of $5 per pound as the cost of producing trout, but that is based on trout raised to a half-pound size.

The medicated feed being used to treat the trout at the Mojave River Hatchery is more than double the cost of the normal feed used. The cost of this feed and the estimated value of the losses is approaching $250,000 just two months into the outbreak.

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