Top of the Food Chain: Dorado (Salminus spp.) in Aquariums
Author: Brian M. Scott
Members of the family Characidae are broadly known as characins, a family that includes interesting fishes like the feared piranhas and pirembebas, fruit-eating pacus, torpedo-shaped Leporinus, the brilliantly colorful cardinal tetra, headstanding Anostomus, and the stout dorado.
Today, it is hardly possible to search the aisles of your local fish shop and not see many types of characins being offered for sale. In fact, many fish shops have tanks dedicated to various species of tetras, silver dollars, and piranhas—all of which are characins. One tankbusting characin you are less likely to see in those shops, however, is the fascinating dorado.
Dorado are insanely powerful, robust fishes belonging to the genus Salminus. Recently there has been some debate about the correct taxonomic validity of several species within Salminus, so in the interest of accuracy I will not get into what species is what. This will not put you at a disadvantage though, as they all require the same basic care and husbandry in aquariums.
Generally, the biggest aquarium possible is best for keeping these creatures. Dorado are capable of attaining total lengths in excess of 2 feet and weights of more than 30 pounds, and if you are a dedicated reader of this column you will surely be wise to the fact that a bigger aquarium is always better when dealing with large-growing predatory fishes.
What concerns me more than simple length is the outrageous power that dorado are capable of unleashing at a moment’s notice. Essentially “tropical trout,” dorado are amazing fish to angle for, and are therefore one of the premier attractions to those traveling to South America for a getaway fishing vacation. This fish’s insane power is turned on in an instant, and when this happens it doesn’t matter if the fish is being kept in a tank or not, it will basically go wherever it wants. So again, to keep one in captivity you will need a really large tank!
I cannot rightfully tell you that a dorado will be happy in a 180-gallon aquarium, nor can I say the same about a 265-gallon aquarium. A small dorado or group of small dorado will appear happy and healthy in such tanks, but not for long. If I had to give an estimate of where said fish would thrive rather than merely survive, it would be a 540-gallon aquarium. And that would be for one or two specimens. However, I have seen them housed in much smaller aquariums for rather long periods of time with great success. As with most large-growing fishes, it’s really something that has to be judged on a case-by-case basis, and what I suggest is just that...a suggestion.
Water Circulation and Filtration
Dorado are best kept in aquariums that have a high-flow filtration system. Since they are naturally found in areas of strong, heavy current, their dissolved oxygen requirements are very high. In fact most large characins have similarly high dissolved oxygen needs. That being the case, supplemental water circulation pumps, like powerheads for example, are a must when it comes to providing a setup for your dorado to thrive in.
Generally the aquarium’s water should be turned over at least 20 times per hour with a good portion of the turnover being directed toward the water’s surface. It’s the surface agitation created by the water movement that will increase the amount of dissolved oxygen in the aquarium. For those of you that are having further problems keeping the dissolved oxygen level high enough, the use of strong aeration will assist in this as well. A good strong supply of air bubbles will always do the trick, and many like the aesthetics of the bubbles, too.
Regarding filtration, dorado are less finicky about actual water quality as compared with some other members of their family. Dorado do best in water where extremes are avoided. They tolerate, and thrive in, water that has a wide range of pH values, as well as nitrate and other metabolite compounds. While my dorado-keeping days have been past me for a while now, I do seem to remember that my nitrates would always read as “off the chart” no matter how many water changes I performed or how much water I changed at a single interval.
They are sloppy fish with even sloppier eating habits, so a strong filter that provides a large surface area for beneficial bacteria is essential. I prefer to have at least two filters on most of my aquariums: one for the removal of suspended particulate matter, to keep the water clear, and another unit to provide effective biological filtration. Since I perform frequent large-scale water changes on my aquaria I tend to not use chemical filtration. However, for those of you who don’t have the time to do water changes so regularly, there are certainly many benefits to using chemical filtrants, such as carbon or various types of ion-exchange resins.
Diet and Feeding
Dorado are carnivores, specifically piscivores. That is, they eat fishes. However, as with even the strictest species of piscivorous fishes, they can easily be trained to accept non-living and even non-fish food items.
Some of the best non-living foods that you can offer large predatory species like dorado are clams, mussels, shrimps, and squid. The food items should always be of the proper size for the fish being fed. That is, don’t throw in a whole squid to a dorado that is a mere 3 inches long.
How to Feed
Once you have selected a food item to try, and have either cleaned the food and/or cut it into the appropriate size for your dorado, you can now offer the food. Do this by placing the food in an area of high current, such as a filter return. Often, hungry predatory fishes will feed based on the movement and taste of the offered item, in that order. In other words, it’s a case of strike first, taste later!
If a small item is moving at a rapid pace, a dorado will often strike it then make sure it is acceptable to be swallowed. So if a small shrimp is placed in the path of a filter’s return, then a dorado will usually strike the shrimp and take it in its mouth. Since shrimp are usually accepted by most fishes, you will usually have little difficulty in getting dorado to eat them. Once a taste has been acquired for the shrimp, other food items can be tried.
Feed dorado a variety of foods. Since one type of dorado, the golden dorado, is brilliantly colored, they will benefit from a wide variety of food items in a way that will also allow their striking colors to develop to their full potential. A large display tank with two or three golden dorado in full color is a hard display to beat. But only a varied diet, great filtration, and a large aquarium will allow such a display to be maintained successfully so your fishes will thrive in it.
In addition to fresh fish and seafood, you will want to introduce some type of prepared food into the diet for dorado. Most hobbyists I know who have kept these fish trained their dorado to take a large pelleted food. Many manufacturers formulate pellets, and the types marketed for large fishes seem to work best.
As dorado grow, and grow, and grow some more, they are less likely to accept small food items, for the energy expended in consuming them outweighs the energy gained from them. For this reason very large dorado, say over 18 inches in length, should have been trained to feed on a pelleted or nugget-type feed many months prior. This way, hopefully they will still find such foods interesting when they grow far too large for many other prepared foods down the road.
Wouldn’t it be nice if all there was to feeding a hungry dorado is to simply lift the lid and toss food in the tank? Unfortunately, that is not the case and feeding dorado can become a complicated task. Remember that these fish are very powerful. If any of you have tanked trout before, you know exactly what I am talking about, and dorado are basically a tropical version of our native trout here in the United States.
Because of their power, dorado often knock decorations over, and even knock lids off of their tank, when feeding time rolls around. Additionally, in their haste to be the first to the food, many dorado will inadvertently injure themselves in the process. Because of this you may wish to keep tank decor to a minimum.
Also, feed small amounts frequently. In past columns on different fishes, I’ve advised this because it’s often bad for fishes to consume large meals on a sporadic schedule. For this article I say it again, partially for the same reason but also because dorado seem to be just a bit less likely to blitz to the top of their tank if they are not quite starving. A good schedule, for example, is to feed your dorado every-other day, just enough to barely see a difference in their stomachs, and then on the other days feed them to satiation. This way there is always some food in their stomachs and they just might only blow one lid off the tank during feeding, rather than all of them!
When it comes to disease, dorado are rarely victims. However, unlike parasitic diseases or bacterial infections and the like, dorado are prone to obesity. Obesity is caused by three main factors: too much food, fatty foods, and lack of exercise.
By far, the single cause of obesity is too much food. I have seen many dorado that quite simply resemble footballs with fins rather than the sleek, rugged, toothy tetras that they essentially are. Instead of the fast-moving blitzkrieg-type super predators, they become more like swimming sea turtles. Dorado in this condition are not going to live long lives.
Dorado should be kept on the thin side—sleek and agile. They need to eat, don’t get me wrong, but feeding them until their bellies are bulging every day, and keeping them in a 75-gallon tank with a simple hang-on filter just ain’t gonna cut it! I will say it again, dorado need big tanks with lots of strong water movement. They essentially thrive in deep river channels, and their setups should somewhat reflect those types of conditions to the best ability of the hobbyist.
Dorado are fascinating fish to keep in an aquarium—as long as they are respected by the hobbyist and kept properly. These fish are no joke, I have seen them bust glass lids to pieces, and I have observed them sail out of their aquariums chasing feeder fishes. Many people say that there is no fish as aggressive as snakeheads when it comes to feeding time. To those people, I say try a dorado!
I would like to extend a special thank you to Mr. Ed Wong for his outstanding photography and patient willingness to work with my last-minute decisions when it comes to selecting a topic to write about each month. Also, I would like thank Mr. Jesse Yang. The dorado depicted in the two photos by Ed accompanying this article are of Jesse’s outstanding specimens. Both Jesse and Ed can be easily found by visiting www.waterwolves.com. I strongly encourage all of my dedicated readers to visit this website, and the others advertised within the pages of my column, for top-quality, factual information on all their predatory fishes! Thanks again Ed and Jesse!
[For an adventurous tale from Ivan Gonzalez and Stan Sung about collecting the ferocious dorado and other monster fishes in their native Uruguay, see “Monsters of the Pampas,” p. 88—Eds.]