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Waspfish, Toadfish and their relatives
14 October 2017
Toadfish and waspfish are distantly related but similar groups of predatory fish found in freshwater, brackish water and saltwater habitats. As the 'toadfish' name suggests, these fish are not brightly coloured and rely on their drab colouration to blend into their environment. The 'waspfish' name reveals another trait shared by the two groups, the possession of venomous spines in their fins used for defence.
Feeding toadfish and waspfish
Venomous fish without bright colours don't sound much like fun, but in fact toadfish and waspfish can be very resilient species that adapt well to aquarium life. However, for all their hardiness, these are fish that can cause problems for casual aquarists because they won't take flake or pellet foods. Without exception, these fish will need suitable live foods initially, and only with patience and persistence will they be weaned onto fresh or frozen foods.
Depending on the size of the fish, good foods to begin with including bloodworms, earthworms, river shrimps and crayfish. Oysterfish will also eat clams, mussels and oysters. Live fish are not recommended because of the risk of introducing parasites. Goldfish and minnows are also rich in thiaminase, an enzyme that breaks down vitamin B1, and over the long term thiaminase can cause severe health problems. Some invertebrates contain thiaminase as well, including mussels, shrimps, prawns and at least some types of squid. Inexpensive thiaminase-free foods including tilapia fillet, rainbow trout fillet, pollack (coley) and cockles.
Weaning predatory fish off live foods requires patience. Initially at least, the main thing is to get your fish feeding. This is where the live foods like river shrimps come into play. Even though shrimps might contain thiaminase, they're easy to gut-load with flake food, so in the short term, they're safe and nutritious.
Once the predatory fish has learned to associate you with its dinner time, you can then move onto offering fresh or frozen foods. Long forceps are useful here, though, a wooden satay stick might be used instead. Either way, wiggle morsels of tilapia fillet or whatever enticingly. With luck, the predator will bite, and once the food is engulfed it should be swallowed as well. Don't be afraid to let these fish go hungry: these fish are well able to do without for two weeks or more, and as the old saying goes, "hunger makes the best sauce!"
It's easy to overfeed waspfish and toadfish. Because they're sluggish animals, they don't actually need much food to stay healthy. Overfeeding can cause water quality problems, and if live foods are used, quickly becomes expensive. In most cases, one or two meals per week will be ample, though the more active Butterfly Goby Waspfish can be fed a bit more often than that, perhaps daily when young, and every other day once mature.
Judging the right amount of food needed by predatory fish can be difficult for experienced fishkeepers. Provide just enough that the belly fills out slightly but doesn't look swollen. When viewed from the front the profile of the belly should be flat to slightly convex, but neither concave nor obviously swollen.
Butterfly Goby Waspfish, Neovespicula depressifrons>
The waspfish family Tetrarogidae is mostly a marine family but includes a few brackish and freshwater species. One of these has become quite common in the trade, the Butterfly Goby Waspfish (Neovespicula depressifrons). These are very nice little fish that rarely exceed 8 cm (4 inches) in length, making them eminently suitable to relatively small single-species set-ups. A single specimen might be maintained successfully in tanks as small as 90 litres (19 Imperial gallons). They also seem to be reasonably tolerant of one another given sufficient space, so maintenance in a small group is certainly possible, allowing at least 90 litres (20 Imperial gallons) per specimen.
One of the good things about the Butterfly Goby Waspfish is its willingness to adapt to life in captivity. It quickly becomes tame, and unlike most other toadfish and waspfish, it will happily go swimming about the tank during the daytime. Feeding is not too problematic; though live foods are definitely preferred, they are small enough to be easily satisfied with earthworms, mosquito larvae, river shrimps and other small invertebrates.
Australian Bullrout, Notesthes robusta>
During the 1980s and into the early 1990s the Australian Bullrout (Notesthes robusta) was a fairly common import, but the author hasn't seen this fish in the UK for some time. To be fair, as aquarium fish go, the Bullrout isn't especially attractive. It is quite big, getting to between 20 and 30 cm (8 to 12 inches) in length, and essentially nocturnal.
They are found in freshwater streams, estuaries and shallow marine habitats. Although the precise salinity doesn't seem to matter much, but they don't do well permanently kept in freshwater conditions, so it's best to aim for a specific gravity between 1.005 and 1.010.
Bullrouts have venomous spines in their dorsal, ventral and anal fins and should be handled with care.
Prehistoric Monster Fish, Thalassophryne amazonica
When it first appeared in the trade a few years ago, Thalassophryne amazonica caused a bit of a stir. Unlike so many other 'freshwater' toadfish and waspfish, this species really is a freshwater denizen, making its maintenance that bit simpler. It is also a rather striking animal, with a pale, mottled brown body and tiny eyes at the top of its head. Because of its weird looks, retailers quickly took to calling this unusual species the Prehistoric Monster Fish.
Thalassophryne amazonica like to hide in the sand with just their eyes poking out above the surface, suddenly lunging upwards when suitable prey comes into range. Under aquarium conditions a suitable bed of lime-free sand is essential, smooth silica sand being ideal. Take care not to use anything abrasive, like Tahitian Moon Sand.
Like other toadfish, Thalassophryne amazonica is hardy and not difficult to keep once feeding. Because of their small size—adults are only 10 cm (4 inches) long—live foods need to be suitable small as well. Livebearer and killifish fry are probably the most economical options, but because these are surface fish, while Thalassophryne amazonica never leaves the substrate, getting predator and prey to meet is very difficult. Thalassophryne amazonica really only goes for prey immediately in front of its face, and that means the best prey will be things that swim about on the sand. Prolific cichlids such as kribs and convicts might be useful here, since they will produce lots of fry that feed from the bottom of the tank rather than the top. Freshwater shrimps such as cherry shrimps that breed readily under aquarium conditions are also worth a shot, though they're far less productive than cichlids and would need to be gut-loaded with flake food to offset any thiaminase content.
Can Thalassophryne amazonica be weaned onto non-live foods? Yes, it's been done, much as with other toadfish, but it takes a long time. Anyone planning on keeping Thalassophryne amazonica must be prepared to supply suitable live foods for a long period, perhaps indefinitely.
While the author has never seen them in the UK, there is another small Amazonian toadfish that might turn up. It is called Potamobatrachus trispinosus and only gets to 5 cm in length. Basic care is presumably similar to the Prehistoric Monsterfish. Do take care not to confuse this small freshwater toadfish with the much brackish water species Batrachomoeus trispinosus. While their Latin names are similar, they are very different fish!
Brackish-water toadfish sold as "freshwater" toadfish
At least two "freshwater" toadfish are seen in the trade Batrachomoeus trispinosus and Allenbatrachus grunniens. Despite being called freshwater toadfish by the less scrupulous retailers, both are brackish water to marine fish, and neither can be maintained indefinitely under freshwater conditions. Aim for a specific gravity of at least 1.005, and in the long term 1.010 or more is probably best.
Telling the two species apart is difficult since they share very similar colouration. Both species can get up to 30 cm (12 inches) in length, but they are not particularly active fish, so a single specimen might be maintained in a 200-litre (44-Imperial gallon) without problems.
Both these toadfish are peaceful towards things they can't swallow, but their ability to tackle surprisingly large prey shouldn't be underestimated. Tankmates should be deep-bodied and as big as the toadfish to be considered truly safe. Adult Scats, Green Chromides and Colombian Shark Catfish would make good companions.
Like most other toadfish, Batrachomoeus trispinosus and Allenbatrachus grunniens are venomous, with spines in their dorsal fins and on the gill covers capable of delivering quite a nasty sting. They are also notorious 'biters' when irritated, so care should be taken when handling them.
At least one oysterfish, Opsanus beta, is occasionally on sale in the larger marine aquarium shops. It comes from the tropical Western Atlantic region including the Gulf of Mexico, and is sometimes known as the Gulf Toadfish. An alternate common name, the Orange Toadfish, refers to the bright mottled orange colouration of some specimens. Not all are bright orange, in fact most are mottled brown, but the ones that appear in the trade tend to be the orange specimens. To a degree their vary their colours depending on their environment.
Opsanus beta is a fairly large predator, with a maximum length of just over 30 cm (12 inches). Their social behaviour is interesting. Males attract females by producing songs consisting of remarkably loud grunts and whistles. After spawning the males look after the eggs until they hatch.
Gulf Oysterfish are not venomous, but should be handled carefully nonetheless because they have strong jaws adapted to crushing shellfish such as oysters, and can inflict nasty bites. They are very hardy animals that live well in captivity, but like any aquarium fish, do best when given good care.