I asked Bill Cody if he would write the first reply - to get the thread started on the proper note. He graciously agreed and put together an extensive response!

Originally Posted by Bill Cody
They write books about this topic. I have a book that 53 years ago, listed known parasites of BG are 9 protozoans, 56 trematodes, 8 cestodes, 11 nematodes, 5 acanthocephalans, and 6 leeches, 1 mollusk, and 12 crustaceans. Known parasites of LMB as 13 protozoans, 45 trematodes, 11 cestoda, 14 Nematoda, 5 Acanthocephala, 4 leeches, and 10 crustaceans. Most of these parasites are not very obvious on or inside the fish. So parasites of just these two fish species can be pretty numerous, thus one should have a concern for transporting or moving fish parasites especially from wild water sources that do not get periodic fish renovation.

The primary parasites will arrive from or be delivered from mainly wading birds. There are numerous other ways that nature and man can introduce parasites to fish in a pond but about 70%-80% usually come in from the waterfowl transport pathway. Fish diseases which are very different from fish parasites and this is a completely different topic. Fish diseases usually arrive from infected or contaminated fish that have been somehow introduced.

Parasites and diseases can be internal or external for the fish. Healthy fish maintained in good water quality have the ability to most often avoid getting or being significantly harmed by fish diseases. Fish in natural waters live in a “soup” that has many natural forms of health contamination. Some water bodies contain more health problems than others. It is hard to know all the sources of contamination from any one water source. The individual contamination “problem” itself goes through highs and lows of population density because it is a living virus, bacteria, or larger organism (parasite). Basically healthy fish are naturally designed to fend off most of the health problems by use of the fish’s continually produced slime coating. Unhealthy or severely infected fish will die and in that process,,, spread the infection. This is similar to the Corona virus problem. Healthy people survive and/or have few affects, of the viral infection and vulnerable people get sick in varying degrees based on their genetic composition and the overall health of the person.

When stocking fish the salt baths are a good way to minimize or reduce but not completely eliminate introduction of the most common parasites and some fish diseases. There are books with numerous chapters that describe and discuss the wide range of parasites and diseases that affect fish. Very few pondowners do salt bath precaution because it takes extra time and effort. Plus very few pond owners know about the need or benefit of doing it. A lot or even most of these wide ranging types of fish health problems are not easily noticed on a wiggling, squirming, wet fish. Very few fish buyers even know what to look or test for when buying and casually looking at the fish. Plus if the fish are coming from a fish farm or hatchery many of the weakest ones have already died somewhere during the holding period before the fish are actually sold or delivered. Many fish farms remove dead fish from tanks each morning. Number of fish deaths is usually closely related to how long the fish have been held in tanks prior to sale. The degree of minimization or reduction of the “problem” from the salt bath is dependent on if the “problem” is external or internal and what or who comprises the “problem”; again some “problems” are external some are internal. Salt and chemical baths are primarily used to reduce the most commonly occurring externally related “problems”. Fin rot problems are usually not cures using salt baths.

The question is: "Is the transfer of parasites from a forage pond to a main pond a legitimate concern?" "If so, what steps should we take to minimize parasite transfer and contamination?"

1. IMO the transfer of parasites from a forage pond to a main pond should ALWAYS be a concern. Why introduce “problems” into the main pond if that particular problem does not already exist in the main or receiving pond?
2. “What steps should one take to minimize parasite transfer”.
For the average pond owner I think the basic and simplest answer is to pay attention to or monitor the basic health of the fish in the forage pond. Are there or have there been any apparent parasites on any of the fish such as black spots and or noticeable adorations or abrasions on the skin or fins of any of the fish that are being monitored in the forage pond? You will not see all the problems. But periodically carefully looking at fish in the forage pond is a good routine policy. The number of ‘infected fish’ indicates the degree of the problem.

Generally my rule is, the longer the forage pond has been active since the last draining or fish renovation the more likely the pond fish will have some sort of parasite / disease contamination. Nature has numerous ways to introduce these health “problems”. Once present these “problems” almost always continue to multiply in the natural setting especially in over-crowded forage ponds. Selling, trading, or giving away infected fish is bad for business and your reputation. Periodic forage fish renovation is really the best plan of managing a forage fish pond. Many of the best fish farms do this every year. Clean out the fish and start over. Plus fish farms are usually dealing with fry to fingerling so fish populations in these ponds are renewed each year or frequently or routinely. This helps a great deal to minimize parasite and disease problems on the commercial and private scale.

The most common visible parasites will be on fish that come from ponds that have common visits from wading birds, which does occur on most all types of forage ponds. The other item to look for or pay attention to is have you noticed any or several sickly, infected, or dead fish in the forage pond? Is it a common or a rare occurrence? Usually in the main community fish pond weakened or sick fish become easy prey items before the infected fish dies so the problem is often not even observed. The frequency of any of these health ‘problems” will determine when it would be most beneficial to use a salt bath when transferring fish from the forage pond to any other water body.

Snipe from his extensive experience with State DNR fishery workers demonstrated the salt bath use in the transfer of forage fish in Snrub’s pond. The salt bath dip is always the best standard and a safe precautionary procedure to use; although it is not a fool proof method due to the wide diversity of health problems that can infect fish. See Snipe’s salt bath technique during fish harvest in this link:
https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=528099&page=12

The other concept or philosophy here is if the receiving pond already has fish with the same parasite problem as the fish in the forage pond then there is IMO less need to treat the infected incoming forage fish at least for the same obvious “problem”; such as black spot parasite, or white, yellow grub. An infected fish is often a weakened fish so a salt bath can be a beneficial thing to routinely use if you place high value on your fish community. This is just my philosophy that I use for my private ponds. However, if you are trading, selling or giving away fish and you have any form of infected fish the salt bath becomes a more important method to use.