Stocking Levels - What’s the limit?

Stocking levels, this is possibly the most confusing and conflicted subject in the hobby, what is right and what is wrong? A short and simple answer, there is no right or wrong, its about finding what works for you and your system and also what is right for the welfare of the fish.

Often do I find people setting up new ponds that come to visit me and more than likely the first question after explaining their setup is “how many fish can I have?” I have always taken the same approach, and questioned what the hobbyist is trying to achieve. For example, we will use a 10,000L system fitted with a nexus 320+ as a standard guide, there is no magic number in regards to how many fish can live within a certain amount of water, too many people are getting caught up on this idea of having say 1 fish per 300 gallons. This isn’t the most effective way of managing things or even judging how many fish you can put in the pond. There are hundreds of variables that would effect the stocking level, which should all be considered before even buying fish, my best advice to any hobbyist or customer, isn’t to think of a number and just stick to it from day one, find what works. 

A big factor when looking into stocking levels is the biological capability of the filters, regardless of water volume, if the biological capacity isn’t sufficient, the pond will have issues and inevitable fatalities due to ammonia and nitrite not being processed properly, this can also then lead to secondary issues, potential bacterial issues or even parasites getting out of control. Fish have got to be fed an adequate diet, throughout winter feeding slows down and would be around a small handful of food per day, just to keep the fish ticking over and their digestive system active. In summer however, this is a different ball game entirely, koi especially will be looking for food throughout most of the day and in most cases could be continuously fed over and over.

Unless pushing for growth, the need to deliver feed into the pond in mass quantities isn’t necessary. As mentioned before, the actual limit is dependant upon what the individual wants to achieve. If taking tosai through to nisai and trying to push for the best growth, ideally you want a heated system that can keep the temperatures stable, as throughout the summer we still see slight variation in temperature at night when it is cooler. Also, feeding levels would be higher too than in a normal garden pond, increasing throughout the season as the fish get bigger and inevitably more hungry. If this is the desire, I would advise starting out with around 20 tosai in the example pond given. However, it needs to be considered that as these fish grow, the amount of ammonia being produced also increases. If the nexus is struggling with the load, then there are a few options that can be considered, the most obvious is the feed, you could cut back on feeding, however if growing this needs to be increasing, not decreasing. The next option would be to upgrade the filter system, I don’t mean by removing the nexus, my suggestion would be to add a shower filter after the nexus and potentially an additional pump directly fed from the pond to push water over to take the stress off the nexus. The third option would be to remove some of the fish in the pond, as it would reduce the ammonia levels being produced. Another factor that has to be included however is how regularly fresh water is being added into the system by either means of water changes, trickle in/out or regular maintainance of the filter systems. 

The pond above would happily deal with 20 tosai gradually growing, without little issue, no heavy feeding or stress on the system would allow the fish to grow at a more natural rate, but again the fish will grow and further down the line the same problems would occur with either moving a few fish on or increasing the biological capacity of the pond. Of course there will be people who buy a set number of fish and grow them and they will be successful, but that is in an ideal world, chances are along the way you will face ph swings, parasites or possibly other factors that could lead to fatalities, or even be drawn into buying additional fish. Water quality issues or parasites aren’t too difficult to irradicate, with the right advice, so I would always advise speaking to a dealer if unsure, as some advice seen on forums is misleading and potentially more dangerous than the issue at hand.

My advice as a dealer, would be to consider what you’re trying to achieve, if you want a pond with a few koi carp in there that allows you to sit by and enjoy your pond, then don’t get too hung up on trying to have as many fish as possible, if you’re really wanting to grow tosai on then by all means do it, its great to watch and a rewarding experience, but be careful and keep in mind that at some point something will need to be changed, whether that be the amount of food going in, the water changes, filters or the stocking level. And then the third option which I haven’t really mentioned as its not overly common, some people enjoy buying big fish - say 70/80cm in length and keeping those. There is often no desire to buy tosai at 12/14cm and see how they develop, but along with this comes great expense. The stocking level in this sort of setup for these kind of fish is probably maxing out around 8-10 fish, before any upgrades etc. There are hobbyists out there who have ran similar systems and been successful with more fish in there, but I wouldn’t advise trying it unless you’re willing to risk a lot of money if a fish was to have complications.