The Effects of Increased Water Flow on Salmon Fry in a Remote Site Salmon Incubator

Problem: Will an increased water flow to 6-8 gallons per minute (gpm) through a five gallon Remote Site Incubator (RSI), as opposed to the normal 3-4gpm, be detrimental to the salmon fry from the RSI?

I chose this project because I have been involved with the working of RSI’s and other salmon enhancement projects for about six years. I have set up and run an RSI at my home for about six years. I also have participated in other salmon enhancement projects. I acted as team leader and investigator in studying benthic macroinvertebrates. I have directed and participated in salmon carcass replenishment for the last three years. I have a strong background in salmon enhancement but wanted to expand my knowledge and opportunities in this field.

A meeting was organized with Jerry Manuel, the head of a local salmon hatchery, to clarify a direction for my project and determine an area of research that had not yet been fully explored. It turned out that Jerry is also the designer of remote site incubators (RSI's). A remote site incubator is an all polyethylene barrel (usually 5 or 55 gallons in size) used for the incubation of salmon at streamside locations. After talking with Jerry, it was determined that it was a concern of his and of other fish biologists, that some salmon eggs and fry are developing problems and diseases from too much water flow in the incubators. I decided to study flow in the new polyethylene barrel type RSI's. RSI's have proven to be very successful and easy to maintain and use, but there is concern that various diseases observed in RSI's may be related to water flow. No actual research has been done to prove if excess flow was the cause, so I decided I would explore the effects of high flow on five gallon RSI's.

These RSI's were designed and fabricated by Jerry Manuel in 1985-'86 for the Washington Department of Fish and Wildlife in response to a problem with older style gravel box incubators. These new RSI's were designed to be far lighter, more portable, easier to set up and clean, and cheaper than the formally used large, heavy gravel box incubators. These new RSI's were rapidly being deployed and set up all around the Hood Canal region. They were originally used to supplement fisheries by increasing the number of chum salmon in Hood Canal so that the fishermen could catch more fish. These RSI's proved to be very successful. They were easy, inexpensive, and had a good egg to fry survival ratio. Due to budget limitations within the Washington Department of Fish and Wildlife, no further testing could be done to find out other advantages or disadvantages about these new RSI systems. Yet, the demand for RSI’s has expanded to areas as far away as New Zealand.

The new use for these incubators is to re-establish native salmon runs. This new intention is brought about from the realization that hatcheries aren't as good as originally thought. It is now realized that hatcheries are a factor in the decrease of wild salmon size and health. Hatcheries take "survival of the fittest" out of play and even weak fish can reproduce. Therefore, hatchery practices are slowly genetically altering the salmon population to smaller, less vigorous and less healthy species. Because of these newfound disadvantages of hatcheries, the RSI's function is not solely for supplemental enhancement. They are now being used in remote areas to help bring back the native salmon. They are doing this by what is called "pumping redds". This is done by taking fertilized salmon eggs out of their salmon nest and placing them into the RSI. Another more favorable method is, taking the native salmon once they have made it up stream to near the RSI and removing the eggs from the female. Then several males are found and used to fertilize the eggs from the female and all the fertilized eggs are placed into the RSI for hatching. This is done because the eggs have a 90% survival rate in a RSI as opposed to about a 5% survival rate in the river. Their carcasses are then placed back into the stream for food for the fry when they leave the RSI.

The average working water flow in these five-gallon RSI's is between 3-4gpm. This measurement was obtained solely by figuring out how much water was needed to provide the eggs and alevin with enough oxygen to survive. It was never tested to find out an excessive or a more optimal flow rate for the RSI. I hypothesize, based on my conversations with salmon biologists, that an increased flow, twice that of normal, may have negative affects on salmon eggs and alevin for several different reasons. The alevin will have to fight more against the upward current of the water to stay down in the substrate. This may cause the salmon to use up their yolk sac more quickly than usual because they are using it for energy to move and stay warm rather than for growing. This would lead to the alevin emerging earlier looking for food and on an average weigh less than the average alevin when it emerges from the substrate. It may also result in a higher mortality rate than the alevin in the "average" flowing RSI. Also, the excess alevin movement in the substrate will cause the alevin to hit and rub their yolk sacs on the hard plastic. This may lead to such things as coagulated yolk, bacterial gill, or even cold temp disease.

Coagulated Yolk, also called White Spot Disease is nothing more than the hardening of the yolk sac before it is used up by the alevin. This renders the remaining yolk worthless before the salmon is fully developed. Not all causes of coagulated yolk are known, but an increased water flow may be a contributing factor to this problem. The coagulated yolk on a salmon seems to interfere with the salmon's ability to maintain covering of its extremities. The fins are usually the first to be affected by this condition and often develop "Tail-Rot" or "Fin-Rot". This can cause many problems including death. Coagulated yolk can also make the salmon more susceptible to other diseases such as Cold Water Disease.

Cold Water Disease, sometimes called "Peduncle Disease" is a bacterium that slowly eats away at the skin of the yolk sack on fry or alevin. This may cause problems such as the spilling of the yolk sac and death. If obtained by the salmon after it has absorbed its yolk, it will have such symptoms as external lesions and loss of tail leading to internal infection and often death. This Cold Water Disease can also attack the gills causing symptoms identical to Bacterial Gill.

Bacterial Gill is exactly what it sounds like. It is the formation of one of several types of bacteria that can form on the gills and interfere with the exchange of gas between the blood and water. The symptoms for such a bacteria are pale color in the fish, loss of appetite, and accelerated gill activity. In advanced cases, it can even cause the complete fusion of the gill filament causing suffocation and death.

I hypothesize that the salmon fry in the RSI with the 6-8gpm will on an average weigh less than the fry coming from the 3-4gpm controlled RSI. There should also be a higher mortality rate of eggs and fry from the 6-8gpm RSI then the 3-4gpm RSI. This phase will be completed in this paper. Phase Two will be completed in February or March as a subsequent research project. If excess flow is detrimental to the alevin, the alevin will use up their yolk sac quicker trying to stay warm and fight the flow and not so much for growing. These alevin from the 6-8gpm RSI may also develop such diseases as Cold Water Disease, Coagulated Yoke or Bacterial Gill due to this increase of water flow while they are in the substrate or the incubator.

The items that will be necessary for this experiment are as follows, two 5 gallon RSI's with all the necessary equipment (piping 2", valves 2", connectors 2", substrate, pea gravel, egg trays & cover). 1'x1'x12' raceway holding tank, divided into two sides to separate salmon fry will be needed along with 7,400 fertilized salmon eggs in each RSI. Some sort of flow meter will be needed for monitoring gallons per minute. A screen to block holding tank outflow, net cover for holding tank and 1 month supply of fish food for all the fish will be needed for Phase Two. An Aculab electronic scale will be used to weigh eggs, alevin, and fry.

My general procedure is to:

Use a site that is already set up with a clarifying tank and plenty of flow so I would just have to hook up my RSI's. It was on a small creek at a Hood Canal Salmon Enhancement Group member's house. He was able to make sure the RSI was secure and functional in my absence.
Set up both RSI's according to the Washington Department of Fisheries Volunteer Fisheries Resource Programs Remote Site Salmon Egg Incubation procedures provided.
Set up the raceway near the RSI so that the RSI outflow will flow in to the two separated sections of the raceway necessary for Phase Two.
Adjusted the valves to 3-4gpm on the control RSI and 6-8gpm on the test RSI.
Pipe the outflow of the raceway back into the stream.
In the raceway connected a 2" pipe to the outlet and elevated to the desired depth of the water (about 3" from the top). Screen it off to allow water to flow through but not salmon fry.
Let both systems operate for several days to ensure all is working properly
Introduced salmon eggs to each RSI. Weighed out 7,400 eggs into each RSI.
Placed them on the egg tray in the RSI
Checked daily on progress and waited for them to hatch.
Monitored hatched eggs and observe alevin swimming down to the substrate
Weighed and measured alevin in the two separate RSI's.
Counted dead eggs and compared mortality rate between the two RSI's.
Phase I is completed.
Obtaining eggs for salmon enhancement isn't easy! It requires permits, etc. Al Adams, Hood Canal Salmon Enhancement Group member had a 55 gallon RSI's right there, he was already slated to get 125,000 chum salmon eggs. He allowed me to transfer my eggs from his larger RSI. I obtained 14,800-eyed chum salmon eggs and placed 7,400 in each of my five gallon RSI's. Because these eggs were eyed they only had a few weeks left until they hatched. I carefully measured the eggs by weight, 7,400 eggs weigh 1,872.2 grams. This weighing method was used to get an accurate and equal count of the eggs in each incubator. The eggs were carefully placed into the incubator until the desired amount was reached. At the time the eggs were placed into the incubator the flow was measured at 3gpm for the control incubator and at 4gpm in the test incubator. The flow was adjusted until it was at the desired 6-8gpm for the test incubator and 3-4gpm in the control incubator. With the eggs in the incubators the only thing left to do until they start hatching is wait. Eggs were checked every couple of days and finally after about a week and a half the eggs began to hatch into alevin. The alevin began to swim into the substrate and the remaining eggs were checked every day until they were all hatched and moved down into the substrate. The remaining dead eggs will be left on the tray in the incubator for several more days to ensure that they are actually dead and not just really late hatchers. When sure that the remaining eggs are dead, the egg tray is removed and dead eggs are counted in each of the two incubators to determine if there is much difference in mortality rate between the two incubators. One can see in the below graph that there was a noticeable difference in mortality as there were 30 dead eggs in the 3-4 gpm and only 23 in the 6-8 gpm RSI.

 The last step in Phase One was to weigh the alevin to see if there is an average difference in size between the alevin in the 6-8gpm incubator and the 3-4gpm incubator and see if there is an alevin mortality difference. The 3-4 gpm RSI shows a drastic difference in alevin mortality about 5,500 dead alevin, and produces noticeably smaller fry than that of the 6-8 gpm RSI, an average of .22 grams/10 alevin less than the 6-8 gpm RSI.

Phase Two began as soon as the alevin from the incubator emerged from the substrate and enter the raceway. Once salmon have buttoned up or used all of their yolk sac they are called fry. The fry were separated into two sides of the raceway between the two incubators. The fry were carefully removed a few at a time being sure to keep the fish separate. They were sent to a pathologist to be analyzed for the diseases discussed above and for any other possible problems to determine if the flow is affecting these salmon in any way.

After the live eggs were all hatched, I removed the egg trays to begin collecting data on the alevin. Everything was normal and there was a fairly low mortality rate. The egg death rate was less than 1%. I weighed an average of ten alevin at a time to get an average alevin weight. I had planned on also taking a length measurement but was told by a HCSEG member that the length of alevin was irrelevant to the project. When I got into the 3-4gpm RSI I observed that there was an apparent, very high mortality rate. It was assumed that this might have been caused by a clog of salmon or silt in the bottom or the RSI against the screen. I decided to take everything out to determine if this was the cause. Along with the help of Al, we carefully removed the salmon and substrate from the RSI into a five-gallon bucket. We expected to find either dead salmon against the screen or a mass build up of silt around the defuser bar. We found none of these. Instead we found that the salmon had died in the substrate and formed a solid mass of decomposing alevin carcasses and so were blocking the flow to the other alevin. After taking all this out to check for the cause I carefully placed the substrate and the alevin back into the RSI. The mass of dead alevin was broken up to allow for the 3-4gpm again. After talking to Al Adams and Bob Rodgers, a Fish Pathologist at Ells Springs Hatchery on the Skokomish River, we came to the conclusion that these fish were suffocated because the 3-4gpm was not sufficient for the 7,400 salmon eggs in the incubator. As a few of these alevin began dying they begin to block the water and soon formed a solid mass of dead and decomposing salmon intertwined in the substrate. This ended up blocking the water flow to the other alevin and so they soon suffocated. This kind of limited my original plans for this experiment so I was not able to get as much data like the weight of the alevin. I was able to get some limited quantities of data and it did show that the alevin in the 3-4gpm were on an average about 2/10 of a gram lighter per ten alevin weighed. At the same time it provided some insight to what is known about RSI's. There is no other evidence that 7,400 chum eggs in a five-gallon RSI with flow of 3-4gpm may not be adequate and needs to be examined further.

Phase Two was the comparison of diseases between the salmon in the two RSI’s. Twelve salmon fry from each group, in the holding tank, were taken to a pathologist on March 11, to be tested for diseases. The results showed no diseases in either group of salmon and so further strengthen my findings. The high end limits have no detrimental effects on the salmon fry. This shows that the high end is actually closer to the recommended than expected because the salmon require more flow than believed. The low end limits do not appear to cause any disease it does increase death rate, lower size and health. This should be further investigated to find the optimal flow rate. Action is currently being taken to inform people of these findings, by rewriting the manual and procedure for the operations of the RSI’s and a web site to inform current owners.  

Works Cited

Adams, Al. Personal interviews. January 1999.
Dermit, Ken, and Howard Fuss. Evaluation of Remote Site Incubators as an Enhancement Tool Progress Report for 1994.
Endicot, Rick. Personal interview. December 1998                             Manuel, Jerry. Personal interview. Nov.-Jan. 1998-‘99                      Manuel Jerry, & Richard Kolb, Ken Demitt, Remote Site Salmon Incubation, 1991.
Rodgers, Bob. Telephone interview. 2 January 1999                        Wampler, Philip L. & Jerry Manuel, A Test of Remote Site Incubators Using Green, Untreated Fall Chinook Salmon Eggs, 1992.
Wood, James, Disease of Pacific Salmon Their Prevention and Treatment, January 1979.

The Effects of an Increased Water Flow on Salmon Fry in a Remote Site Incubator

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