Disease Tolerance of Pathogen-Free Fish

We have had a few questions where customers expressed concerns that our disease-free fish would have no immunity to the diseases in their tanks and would get sick more readily than fish that had been previously exposed to these pathogens. We certainly haven't made the huge effort required to have disease-free fish just to have them do poorly in other's tanks. So, let's look at this a little more closely.

There are no scientific studies on this that we can refer to. Heck, there may not be another disease-free hatchery in this country, so it's not something that would even be a concern until just recently. However, let's be clear. The reason people wonder about this subject is not that people are experiencing sick fish from our hatchery. It's just a concern based on suppositions.

We've shipped tens of thousands of fish that have come from our disease-free hatchery over the past decade. This gives us a pretty good base to come to some conclusions. We've had plenty of feed-back and can easily compare it to when we had a very healthy hatchery, but not one where we were sure there wasn't a pathogen of some type present. We've always quarantined to an extreme and treated for any possible parasites and other pathogens, but it's only been about a decade since we've instituted our new techniques for obtaining pathogen-free eggs from fish and then transferring these eggs to a hatchery that has never had anything other than these clean fish eggs entering it.

We need to point out that people who received our fish are given no guarantees to not have a problem. No matter how disease-free they are when we ship them, they can become sick and die when exposed to virulent pathogens or poor care. There are also opportunistic bacteria everywhere waiting to pounce on a stressed fish. These are not virulent pathogens, but quite capable of overcoming a fish that has a compromised immune system from too much stress.

The big question is, does exposure to virulent pathogens and opportunistic parasites give some degree of immunity to fish down the road? With some pathogens, like viruses, there is no question. Yes, immunity will develop. But with any virulent viruses, the goal is to never expose them to the virus. Viruses have no cure and exposure at any point is very undesirable, since the fish seldom survives the infection. Even if they survive the virus, they are of little value after exposure. With every other common pathogen that we can think of, either that pathogen is not designed to kill the fish or it is no indication of an advantage to having the fish get sick at an early age. In fact, getting sick when young and in the highest growth stage is about the worst thing we can think of. We'd much rather have them grow up in the best pathogen-free conditions and be strong fish with capable immune systems able to better handle any pathogens in the future.

What we have experienced: Our fish have a very high survival rate. With no pathogens in the body to attack the stressed fish, they go through shipping like a walk in the park. Normally, when they arrive they are ready to explore, eat and some (mature fish) are even ready to spawn within hours. We've had a lower than the normal number of people call with problems and most problems crop up much later down the road. Fewer people have complained about fish getting sick and dying (at any point). Without a doubt they are being exposed to pathogens in customer tanks. It is the rare customer who quarantines in a manner where our fish are never exposed to a pathogen, yet we've experienced greater customer satisfaction than ever before. While this is not a scientific conclusion, it is based on actual outcomes. We can say with confidence that pathogen-free fish are not more susceptible to getting sick when exposed to them at a later time in life. We believe it is an advantage to stay disease-free as long as possible before exposure to any problems.