Basic Tips for Successful Spawn Taking

Neil Van Gaalen
Former Hatchery and Brood Station Manager Colorado Division of Wildlife

During my tenure with the Colorado Division of Wildlife I accrued more than 30 years experience in taking spawn. I found that good techniques will result in less than a 10% pick-off. These tips cover two categories; wild fish spawning in natural conditions and domestic spawners raised in a hatchery environment.

The natural diet of wild fish gives them high quality eggs which will result in a very low pick-off. These fish are caught in fish traps placed at inlets or outlets of lakes or they are caught in rivers. When taking eggs in an open environment the sunlight shining on the spawning pan can have a negative impact on the fertilization process. This is particularly true in the late spring or summer when the sun is very strong. During this time it is advisable to construct a small shelter to protect the spawning pan from direct sunlight.

The fish should be presorted to separate the ripe females from the green ones before the spawn taking begins. Normally, when a female is ready her belly will become very soft. Separating the ripe females ahead of time enables the spawning process to proceed at a fast rate. The reason, of course, is to reduce the time that it takes for the eggs and sperm to come together. I have always used a glove on my left hand (I am right handed) in order to be able to hang onto the tail of the fish better while using my right hand to strip the eggs. Forcing the eggs from an unripe female is bad news.

For optimum fertilization, eggs from a couple females may be stripped into the pan and then be fertilized with a couple of males. More eggs may be added with additional sperm. Then the eggs should be rinsed in clear water to remove the sperm, placed in a container of clear water and allowed to water harden.

Successful spawn taking has to be a well orchestrated procedure. Once the physical conditions are met i.e. protection from the sun and separation of ripe from green females, the timing of each step becomes crucial. The time the eggs are first stripped into the pan until they are rinsed should not exceed 3 minutes. The number of eggs that go into the pan depends on the stripper. The life of the sperm depends on its exposure to water and in my opinion, that time frame is about 20 seconds. This brings up another important factor. The pan ,of course is wet, but there should be no standing water in it at the beginning of the stripping procedure. This would shorten the life of the sperm and thus produce a negative impact on fertilization. It is advisable to mix the sperm into the eggs by hand to assure that all the eggs are exposed to the sperm. Then the eggs are rinsed and placed in containers to water harden. The hardening process takes about one hour.

The eggs should be transported to the hatchery as soon as possible after they are water hardened. Remember, the water hardened eggs are beginning to get tender and should be handled with care. I prefer to transport eggs in a sealed container filled about half full with eggs and the balance with water, leaving no room for air in the top of the container. This keeps the eggs from sloshing around during transportation.

When the eggs reach the hatchery they should be put in incubators and not handled until they are eyed up. The reason for this is that the eggs go into a tender cycle when any physical movement to dead eggs will also kill live eggs. This is a vicious cycle that can result in a high loss of otherwise good eggs. Experience teaches that eggs with less than a 10% pick-off produce higher quality eggs. Situations where the pick-off is 30 to 50% or more usually result in very poor egg quality in the surviving eggs and on through the hatching process.

During the incubation period (remember, don’t disturb the eggs in any way until they’re eyed up) some eggs will turn white which indicates that they are dead. When the eggs are eyed up it is normal to submit them to a mild bump that will cause the infertile eggs to turn white. At this point, all of the white eggs should be removed.

If you put a white egg in a strong vinegar solution the egg will turn transparent and it will be easy to see what stage of development the embryo was in when it turned white. If no embryo is present, or only a white spot shows, it usually means that the egg was not fertilized or that it was injured in some way at the very beginning stage of incubation.

The actual taking and fertilizing of the spawn is the same for both domestic and wild fish.

Many fishery operations are taking rainbow trout during the fall and winter. The Rainbow is naturally a spring spawning fish but when held in constant water temperatures of around 50 degrees F, the Rainbow will gradually change to a fall and winter spawner. These fish can be further manipulated with the use of enclosed sheds with artificial lighting over the raceways or structures where the fish are being held. The enclosure must be totally dark with the only light coming from electric light bulbs. A timer is used to produce the desired amount of light for the length of time needed to further regulate the spawning.

I would like to point out two very important items relative to the enclosed fish:

1. The water temperature for this type of operation must be constant around 50 to 55 degrees F year around. If these fish are held in an area where the water temperature is ideal during the summer but starts dropping in the fall of the year, such as is common in streams, the spawning results will be very negative. The fish that are starting to spawn will not continue to do so properly. Holding their eggs abnormally long will cause the eggs to water harden in the fish which will result in a total loss of eggs.

2. The diet of the fish is very important in maintaining a hatchery brood fish operation. In my opinion, the fish should be fed fish food that is specifically prepared for a spawning operation by a company that has a satisfactory record of producing this fish food. My experience relative to the standard fish food (pellet type) used in a brood fish operation can result in high egg mortality, soft shelled eggs and an abnormally high mortality rate in the brood fish.

The training of personnel in the actual egg stripping process is very important in both wild and hatchery brood fish operations. It is my feeling that all strippers must develop their own sense of touch to be able to determine when a fish is ripe. Remember, forcing eggs from a female before she is ripe is very bad news.