Attack of the Green Munchers! 10 Plant-Shredding Fish

Author: Amanda Wenger

A well-planted tank is a beautiful thing: a miniature ecosystem unto itself. However, when it comes time to add the fauna to complement your dazzling flora, take some time to consider that not every fish is plant friendly. The reasons for this vary from rampant herbivory to size- and behavior-related collateral damage. Regardless, some fish are just not cut out for life in an aquatic jungle. Let’s take a look at some of the worst disruptors of otherwise harmonious planted tank setups.

1. Goldfish (Carassius auratus)

No matter how big and well maintained your setup is, it’s best not to place plants in goldfish tanks except when providing them as food. Goldfish (Carassius auratus) are not pure herbivores, but they are voracious omnivores. When they decide that they haven’t eaten enough, plant salad is definitely on the menu.

Even if they don’t like the taste of a particular plant, in the wild they love to root around in the substrate hunting for worms and crustaceans and they will do the same thing in your aquarium. Anubias spp. at first look like a safe bet to keep with goldfish, as these plants are epiphytic, meaning they attach to rocks and driftwood. They also have tough leaves laced with raphides, which are crystals of calcium oxalate that some plants produce as a defense mechanism. The needle-like crystals jab and sting the mouths and throats of any oblivious animal that takes a nibble, the reason for such plants having common names like dumb cane (Dieffenbachia spp.).

Still, for every success story I’ve heard of goldfish and Anubias being kept together, there’s another where the goldfish tore up the Anubias plant for no reason other than they could. Since results vary, I would err on the side of caution and avoid putting plants and goldfish together in a tank.

2. Mbuna

If I tried to individually list all of the mbuna (haplochromine cichlids from Lake Malawi) that are hazardous to plants, this article would be called “1000 Fish to Avoid for Your Planted Tank.” Mbuna are voracious herbivores; in their native waters, they mostly eat forms of algae attached to the rocky lakebed, but they will eat any plant they see. I keep a tank of mbuna just to use as a waste disposal for all of my overgrown floating plants.

Some hobbyists report success with Anubias in their mbuna tanks, but more often than not, the fish will even nibble those plants, although I’m not entirely sure how they get around the raphide problem. It may be that each fish takes just one bite and decides not to continue. Even this will quickly destroy a plant, since mbuna tanks tend to be densely stocked to prevent any one fish from becoming a target of its tankmates’ aggression.

I also hear occasional stories of varying degrees of success with Java fern (Microsorum pteropus), Bolbitis, and vals (Vallisneria). The first two are tough-leaved ferns, but the last is decidedly edible—another common name for the assorted val species is water celery. Still, the vast majority of mbuna keepers don’t spend their time or money experimenting with plants in their aquariums.

3. Oscars (Astronotus ocellatus)

The South American oscar is an incredibly popular cichlid in the hobby because of its intelligence and individualistic personality, and its carnivorous diet may lead to hopes of keeping it with plants, but this fish has one big flaw: It fancies itself an interior decorator. If any of the dÉcor is small enough to be picked up by an oscar, it’s a pretty sure bet that the oscar will impose its will upon your meticulously placed tank layout sooner or later (and probably sooner). Any plants in the substrate will be dug up, torn out, or otherwise mauled.

Even Anubias plants aren’t safe, because oscars will tear off the leaves or yank the rhizomes off whatever they’re attached to. Sometimes it doesn’t happen right away and you can keep a plant in there for a few months, but oscars are also known for being moody: After three months of ignoring a plant, an oscar might just decide it’s fed up with those annoying green leaves and decimate it.

4. Uaru spp.

The triangle cichlid (Uaru spp.) is another large South American cichlid species, but unlike the oscar, it causes difficulties in planted tanks because of its diet, which mostly consists of vegetable matter. They display many interesting behaviors, including feeding their young via a slimy coating much like the more popular discus. In fact, the triangle cichlid was known as the “poor man’s discus” before captive breeding of discus drove prices down. Uaru spp. cichlids are best kept with plants of the artificial variety.

5. Leporinus spp.

A fair number of myths exist in the hobby when it comes to the genus Leporinus. One I often hear in pet shops is that banded leporinus (L. fasciatus), the most common species of this genus in the hobby, will only reach a modest 6 inches (15 cm) in length; in fact, they actually get to about a foot and a half (half a meter) in length.

Rumors of their compatibility with plants are also off the mark. Leporinus spp. are omnivorous, and young specimens in particular (the ones you see for sale) are known for favoring a plant-heavy diet.

6. The Common Pleco (Hypostomus plecostomus)

While some of the smaller omnivorous and carnivorous plecos can be kept in planted tanks with careful attention to plant selection, the common pleco is far too large and clumsy to make a good planted tank candidate. As an omnivore, this fish will nibble at tender plants and rasp sturdier plants with its sucker mouth. It can also reach an alarmingly large size of about 18 to 20 inches (45 to 50 cm) in length.

It’s a nocturnal fish that shies away from observation during the day but roams at night, bulldozing the dÉcor along the way. Plecos like to create hideaways by digging beneath objects. Male plecos frequently signal to females and make territorial displays by wagging their tails with fins fully extended. While a 3-inch (8-cm) clown pleco doing this is harmless, a foot-long (30-cm) common pleco’s wagging will sweep away substrate in wide swaths, which doesn’t contribute to a plant-friendly environment.

7.Silver Dollars (Metynnis spp.)

The various silver dollar species are classic candidates for a list of plant-devouring aquarium fish. As is typical of members of the family Serrasalmidae (the meat-eating piranhas are the exception rather than the rule for this family), their diet in the wild consists of fruit, nuts, and miscellaneous vegetable goodies that they happen across. If you add silver dollars to your planted tank, your flora will become part of its diet as well.

8. Buenos Aires Tetras (Hyphessobrycon anisitsi)

The vast majority of tetra species (characins) are perfect for the planted aquarium. They love to dart in and out of plant thickets for shelter, their schooling habit creates a lot of action in a large aquarium, and the bulk of their diet consists of insects, fry, and other small, meaty things. But this is only true for most tetras; a handful of species are far more inclined to feast on a salad-based diet, and of these, the Buenos Aires tetra (Hyphessobrycon anisitsi) is by far the worst offender.

I learned this lesson a few years back when I attended a regional fishkeeping group’s auction that ran a few hours longer than scheduled. Those of us who had stayed the duration of the event were exhausted, but our endurance was rewarded with low-cost bags of fish. Not all of the bags were well labeled, however, and in the interest of moving things along, I picked up a bag described merely as “tetras,” figuring they’d get along with the other small shoaling fish that inhabited my 120-gallon (454-liter) planted tank.

The tank was heavily planted with a lush carpet of Sagittaria in the foreground and already housed a number of other tetras, so when I finally got home after midnight, I quickly acclimated and added the small group of 2-inch (5-cm) tetras with washed-out colors and promptly fell asleep.

Fortunately, I didn’t have work the next day, so after I had a nice long lie-in, I went down to the fishroom and had to pinch myself to see if I was actually awake: There was my tank, and in it were the shredded remnants of my once-gorgeous Sagittaria carpet and a handful of fat, happy silver tetras with bright red fins and distinctive black diamond marks on their caudal peduncles. Overnight, they’d settled in, colored up, and promptly set out to eat the delicious buffet I had unwittingly provided them.

Needless to say, the fish were promptly removed to a smaller holding tank with plastic plants, and I contacted a hobbyist friend who I knew had plenty of unplanted tanks and asked if she would be willing to take them. Fortunately, she had room, so the tetras ultimately found themselves another abode far, far away from my aquatic jungle.

9. & 10. Scats and Monos

I list these two fish together because, from a husbandry standpoint, they’re practically the same. Scats (genus Scatophagus) and monos (genus Monodactylus) somewhat resemble the carnivorous blackwater discus and angelfish, respectively, but they are brackish fishes with a decidedly omnivorous diet that includes plants.

Few plants can tolerate truly brackish water, and scats and monos need increasingly saline conditions as they mature. There is no such thing as a fully aquatic euryhaline plant (capable of adapting to both fresh and saltwater) in the hobby, so a long-term setup for these fish would be impossible to maintain. If you had a particularly large, well-lit setup, however, a handful of emergent, unpalatable plants like mangrove seedlings and marsh grasses would be suitable—but the scale required for such a setup is better left to a public aquarium than a hobbyist tank.

Do Your Research

While the 10 fishes mentioned here are top contenders to keep out of planted tanks, there are more than just these to consider. Always research fish carefully before adding them to your aquarium (learn from my Buenos Aires tetra experience!) and see if they would pose a threat to any of your plants and/or livestock.