Little Fish Going Crazy in Tanks, What is Wrong?! Little Fish Going Crazy in Tanks, What is Wrong?!
21 June 2021

Little Fish Going Crazy in Tanks, What is Wrong?!

Written by: Fabiola Torres

A few weeks ago, I spoke about the technicalities of pond culture, where I pointed out how delicate and complex it could be to successfully grow endangered Lost River and Shortnose sucker in ponds. However, before fish are set in ponds, they are taken out of the wild and dropped into tanks. The Klamath Falls National Fish Hatchery sucker recovery program depends on capturing very small (approximately 12 millimeters total length) juvenile fish from Upper Klamath Lake. T

his is the life stage where the sucker fish population is declining. The poor habitat conditions found in the lake cause few young suckers to survive to sexual maturity, and therefore, the population size does not increase in the wild. The US Fish and Wildlife Service Klamath Falls Field Office concentrates its efforts for growing this juvenile population in tanks and ponds to help the overall population increase once they are released back into the wild at an older stage where they can thrive.

Once the captured juveniles are in the tanks, they are fed and taken care of until they are ready to be placed in ponds. While in tanks, the staff have noticed something called the corkscrew behavior which is fish randomly swimming in circles. This behavior is thought to be associated with different detrimental factors. However, after discarding factors that are already controlled for at the hatchery, the conclusion is that some fish may be suffering from thiamine (vitamin B1) deficiency. In my last document created as part of this fellowship, with the help of biologists, I created a Standard Operating Procedure to reduce thiamine deficiency in fish in tanks and analyze samples. There are a few reasons that could point out why juveniles are presenting thiamine deficiency: it could have been passed down from the mother, Aphanizomenon flos-aquae blooms that produce something that breaks down thiamine or the food that is being given to the fish lacks the vitamin or the necessary amount of it. To study this theory, we looked into the Otohime brand fish diet that is being given to the fish which seem to lack this vitamin. Then, we looked into supplements that are being used for this deficiency and we found that soybean oil, Otohime B1/B2, and thiamine baths could be our best route for our circumstances. As previous studies have shown, thiamine bath treatments are effective in controlling for this factor. Thiamine baths were the main focus of my SOP and it included protocols for conducting thiamine baths and to sample for thiamine analysis before and after thiamine bath treatments. 

It is also important to mention that once the juvenile fish are transferred to the ponds, the proper management of ponds will continue to provide healthy thiamine levels to fish. Fish feed on plankton in ponds that also depend on good water quality to produce desired thiamine levels to serve as vitamin for fish. If the ponds are not well managed, thiamine levels on plankton will decrease, thus not providing the necessary thiamine levels for fish survival.

I am proud to say that the conservation efforts done by the Klamath Falls Field Office have helped prevent the species from extinction. However, both Lost River and Shortnose sucker continue to encounter severe threats to their survival. I am hoping the work I managed to do for the office will help in reducing more factors that cause mortality of juvenile fish. 

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Aquaria where juvenile suckers are being kept in the facilities.  


On an unrelated note: We still have one Latino Conservation Week up and running! The Bruin Audubon Society and Birding Club has the Family Activity Box + Raffle / Caja de Actividades Familiares + Rifa! Please check out the activities on their website and participate in the raffle!

Agency: U.S. Fish and Wildlife Service

Program: US Fish & Wildlife Service - DFP

Location: Klamath Falls Field Office

MANO Project
is an initiative of Hispanic 
Access Foundation.

P: (202) 640-4342