During recent weeks, there has been considerable question regarding the proper diet and feeding of captive piranhas. So I wrote a little essay about it. What follows is a brief overview of what you, the hobbyist, need to know, and understand, in order to provide a happy and healthy captive environment for your piranhas.
Piranhas are for the most part, carnivores. That is, they consume flesh from other animals in order to fulfill their dietary requirements. In nature, piranhas feed mainly on whole fish and fish parts. What is valuable to understand most can be broken down into two main points: First, just because a fish is a carnivore, does not mean that it's a predator. Without trying to cause mass confusion, please let's clarify that in this case (with piranhas), they are predatory in nature. But how predatory? Second, piranhas eat far more fish flesh than any other type of food. Why? Well it is safe to say that there are far more fish to be eaten than cattle, capybara, storks, or even ducks. Piranhas are fish, they live among many hundreds of millions of other fishes, and they eat fishes.
HOW PREDATORY ARE PIRANHAS
Certainly we all have watched the poor mouse swimming frantically across the top of the water only to get ravaged by Satan's goldfish several times on videos and/or in sequence pictures posted here and other places among the WWW, but seriously, does mammalian flesh make up a considerable portion of wild piranhas diets? No, it does not. Neither does the flesh of birds, amphibians, nor reptiles make up a considerable amount of any species of piranhas regular diet. Now in extreme circumstances such as a drying lagoon in the peak of the dry season in the Llanos of Venezuela, maybe. I think it not too wise to consider home aquariums an extreme circumstance however.
Piranhas are better scavengers than they are pursuers. For this reason, a sub-grouping is in order for them. While piranhas are no doubt predatory in nature, they are also well adept at scavenging and therefore are referred to herein as opportunistic predatory scavengers (OPCs). OPCs are known for their uncanny ability to hunt down the weak, dead, or dying animals in their elements. With great sense of taste, good eyesight, and a remarkable ability to detect nervous, abnormal motion in their environment, certainly, piranhas are very well suited for such a task.
Very rarely will normal, healthy piranhas hunt down normal, healthy food. This is so in aquaria due to the confined space, however, in nature, the flow of energy (energy dynamics) is much more important to their survival and this topic is way out of the scope of this mini-article. More another time on this issue.
CAPTIVE DIET OF PIRANHAS
That said; the diet of captive piranhas should consist of at least 95% whole fishes or parts of fishes. These can be varied but some species are more nutritious than others. For example, some good choices to feed your piranhas regularly are those that have what is called "white" flesh. These include but are not limited to: catfish, sea bass, striper, flounder, scrod, blackfish (tautog), halibut, and Tilapia. These fishes are bland but nutrient packed and offer a near complete diet with the only exception being the lipids and fatty acids that are found in organ meat.
Then we have "pink" fleshed fishes such as: Salmon, trout, sea trout, and orange roughy. Those species that have "pink" flesh are usually fine to feed piranhas in captivity provided that they are fed fresh, very fresh, as the oils that are contained in these fishes are heavy and can cause considerable pollution in your aquariums. The feeding of these fishes to your piranhas should be limited or avoided all together if you cannot clean up after their meal. These meats will definitely cause an oil slick on the surface of your tank's water so be cautioned.
Finally we have "red" fleshed fishes. These include: Mako, swordfish, marlin, tuna, and all other sharks and billfishes. These meats can be extraordinarily messy to feed and they often release high levels of blood and other juices into the aquarium. The tanks often stink within hours of feeding such foods and they are best avoided all together.
WHY NOT MAMMALIAN RED MEATS OR POULTRY?
Aside from not being a natural food source, mammalian red meats are often high in hormones and fats. These will cause undesirable weight gain and retention in captive piranhas to the point of obesity and ultimately a premature death. They often have very high pollution associated with their use should a hobbyist not remove uneaten foodstuffs after feeding. All in all, stay away from these meats except for a rare treat. For these reasons, red meats and poultry should only make up 2-3% of the piranhas diet in captivity.
The same can be said about organ meats as has been said of red meats and poultry. Captive piranhas will get all of their dietary requirements that organs provide through the regular feedings of live/frozen/fresh-killed whole fishes. Foods such as beef heart, lung, liver, and intestine should NOT be a part of piranha’s regular diets in captivity.
HOW MUCH? HOW OFTEN?
As a general rule of thumb, smaller piranhas need to feed more frequently than larger ones do respectively. There exists no magical chart, table, or graph that depicts such a feeding schedule and don’t be fooled into believing there is (by anyone). This is something that you will have to formulate on your own. It is strictly trial and error. If you feed you 5” cariba six times a week and they look as if they are ready to pop after each feeding then you are probably feeding too much, but maybe not. There are variables that come into play.
The only generally safe statement to be made here is that when feeding your piranhas, feed to satiation, that is, round out their bellies. Do NOT make them teeter-totter on the bottom of their aquarium and do not feed them until they start to vomit. When you notice a slight rounding out of the belly then stop. They have had enough, usually.
VARIABLES IN FEEDING
Just as in humans, normally more active piranhas require more food than do conspecifics that are less active. If you have two identical aquariums, both with six 10” piranhas each and the only difference being that one had a flow rate (filter’s turnover rate included) of 1000 GPH whereas the other had a flow rate of 2000 GPH. It would be true to say that the piranhas in the aquarium with the higher flow rate would require more food than those in the other aquarium. Why? Because of energy usage and energy dynamics.
Another variable in feeding your piranhas is water temperature. Since piranhas are cold-blooded, that is, they have no thermal regulatory device for maintaining internal temperature, they are directly influenced by their thermal metabolism and how it processes foods. The higher the temperature is, (to a point) the faster the metabolism. The colder the temperature is, the slower the metabolism.
WHAT IF MY PIRANHA IS OVER WEIGHT?
If you are, or have been, over feeding your piranhas then stop feeding them so much and so often. Small, frequent feedings are better than large, sporadic feedings. Piranhas fall somewhere in between that statement and it is up to you to figure out their optimum balance. Another good thing to do is to increase (slowly if possible) the water flow as to provide exercise to your piranhas. This increased water flow will force them to use more energy and shed some pounds (or ounces) off their bodies. If your tank is heavily planted or decorated then you may need to open it up a bit so the fish are forced into the open. The end results will prove to be healthier, happier piranhas and happier, more educated hobbyists.
Happy piranha keeping!!!!
**This essay was prepared by Brian M. Scott, TFH Publications Inc. exclusively for Piranha-Fury.com***
This post has been edited by B. Scott: 08 November 2003 - 12:01 AM