Eyeballs On Oddballs: A Whale of a Nasty Fish Derek. P.S. Tustin

subfamily Cetopsinae, the distal ends (basically the Introduction trailing or end edge) of both the first dorsal ray (first Recently, I made a trip to Lucky Aquarium in the Market “spine” in the dorsal ray), and the first pectoral ray, are Village next to the Pacific Mall in Markham, Ontario elongated into filaments. Unlike most members of the (www.luckyaqurium.com). That store usually has an subfamily Cetopsinae, these filaments are present in interesting selection of oddballs, and in addition to the both the male and female, but C. coecutiens males tend prehistoric monster fish (Thalassophryne amazonica) to be more slender in appearance, and the above mentioned in the January issue, there was another mentioned filament on the tapers to a finer extremely unique fish in stock. point. The colouring is as detailed above, and they have eyes (which are very small – sometimes described as While it took me some detective work to establish the true “pig-like”) situated on the upper surface of the head. The identity of the monster fish previously mentioned, this eyes are visible when the fish is viewed from above, but other oddball was clearly labeled as “Baby Blue Whale”. not when viewed from below. The body is described as I jotted the name down, and went home to do some being “naked or devoid of scales”, and this results in the research. Friends, if ever I have found a fish that fish having a particularly slimy skin. The mouth is very emphasizes the logic and necessity of doing your large when compared to the rest of the body, usually with research before you buy, this is it. the width of the mouth being equal to one half the length of the head. Nothing is known about the breeding habits or methods of these fish, either in their native habitat or Description in captivity. The twelve or so fish in the tank at Lucky Aquarium were all between 10 and 12.5 centimeters (4” – 5”) in length. They were very streamlined in shape, with the dorsal surface being a turquoise blue in colour, and the ventral surface a milky white colour. However, the truly odd aspect of their appearance was the very small inset eyes, and the round mouth that appeared to be more of a wound than a true mouth.

With a bit of research, I found that the Latin name of this fish is actually coecutiens. Cetopsis is derived from the Greek “cetos” meaning whale and “opsis” meaning likeness, or basically “whale-like”. The name refers to the shape, which is similar to some whale species, and has been described as cylindrical, torpedo or cigar shaped. It is actually a native to the river channels of the Brazilian Amazon that is usually found at depths ranging from 2 – 40 meters (6.5 – 131 feet). Locally they are extremely common, but are rarely imported.

Photo: silurus.acnatsci.org

We all know that body characteristics of the fish we keep tell us something about both their environment and feeding characteristics. In all likelihood, none of the members of the Durham Region Aquarium Society have kept a fish like this. The natural feeding habit of these fish is to bite lumps out of larger river channel fish such as pictus cats (Leiarius pictus), tiger shovelnose catfish

Photo: www.zoopet.com (Pseudoplatystoma fasciatum) and red-tail catfish (Phractocephalus hemilopterus). It is reported that these As suggested by the body shape, these fish are found in fish swim towards the body of the target fish, bite the water with fast currents. Like many members of the body of the target fish, spin their body like a cork-screw

Tank Talk – March 2009 4 Volume 36, Number 7

to tear out a piece of the prey, and then swim away. the armoured catfish family, and then leaving it to be a Apparently they will continue to worry the same wound, potential target and/or prey for the baby whale catfish. taking deeper and deeper bites from the same location until they burrow a hole into the side of the target fish. It has been reported that these catfish have actually been Feeding found inside the body cavities of the larger fish and that The only advantage that these fish seem to have over they may actually burrow into larger fish, eating them some of the other rarely seen oddballs is that feeding from the inside out. The inset eyes and slimy skin make them seemingly presents no problems. As mentioned, it easier for the baby whale catfish to get in and out of they should be kept in a species only tank as they will the wound cavities, and the mouth makes it extremely attempt to eat any other fish, larger or smaller, that share easy to bite out a piece of the target fish. their space. However, their voracious appetite is not

limited to live prey. They will willingly (even eagerly) In nature, they form large schools. While difficult to accept other meaty foods such as chopped mussels and duplicate in home aquariums, it is recommended that live earthworms. They can be easily weaned onto you do keep these fish in groups, but only in a single processed foods, such as frozen meaty foods and species tank. And remember that these fish hunt by shrimp pellets. But even with this, care must be taken as biting. Be extremely careful when performing tank they will gorge themselves if given the chance and you maintenance or you may find some flesh missing from therefore must not overfeed. your hand.

Other Species Tank Set-Up There are at least twenty different species of known As mentioned, these fish come from rapid flowing water, Cetopsis, but several have very little information and in the home aquarium you will need to duplicate available on them. In all the time that I have been these conditions by providing a strong current with high wandering fish stores, I have never seen C. coecutiens levels of dissolved oxygen. Powerheads located at one except at Lucky Aquarium, and have never seen another end of the tank and running along the length can assist member of this species anywhere. It is reported that in duplicating the required current, while filter returns that there are a few colour morphs of this species including agitate the surface can help with the level of oxygen green and tiger-striped. required.

To me this was a very interesting fish to research and Keep in mind that these fish are carnivores and as a read about. It emphasized that there are so many result will produce higher levels of waste. You therefore unique facets and adaptations possessed by fish around need to maintain excellent water quality, with frequent the world. Many we can never keep, but this rare and water changes (at least weekly) of a minimum of 25%. unique fish, for all its specific requirements, is one that allows us to cross from observing the more common fish A tank with dim lighting, few decorations, and plenty of to keeping a creature that showcases adaptations that open swimming space is recommended. There are no are not often observed. Should you have the time, specific requirements relating to the substrate, so inclination and resources to keep the baby whale catfish, common aquarium gravel is suitable. The dim lighting is it would surely be a unique and rewarding experience. recommended due to the relatively poor eyesight of these fish and the fact that they are found in relatively deeper waters in their natural habitat where little light Species Profile penetrates. Latin Name: Cetopsis coecutiens As these fish swim in open waters, you will want to Common Name(s): Baby Whale Catfish, Blue Shark provide a longer tank. Given that these fish can grow up Catfish, Peruvian Blue Shark, to 30 cm (12”) in length, and given the most commonly Blue Torpedo Catfish, Blue available size of tanks, I would recommend a minimum Whale Catfish, Whale Catfish size tank measuring 1.2 m (4’) in length with a minimum Size: 350mm (12“) o o o o width of 45 cm (18”). Depth doesn’t seem to be as Temperature: 22 C – 26 C (72 F – 79 F) important, but 45 cm (18”) seems reasonable. PH: 6.0 – 7.4 Remember that the more you keep, the greater the size GH: 36 – 269 of the tank required. Diet: Frozen foods, shrimp pellets, chopped mussels, live earthworms. Suitable Tank Mates However, it will always prefer In doing research on the baby whale catfish, the live prey, especially smaller fish. common consensus is that these fish should be kept in a species only tank. While some sources suggest that Distribution: Major freshwater rivers including they could be kept with armoured catfish, I would the Amazon and and personally recommend that this not be attempted. I other rivers in Boliva, , cannot see the logic in paying for a unique member of , and .

Source: Various Œ

Tank Talk – March 2009 5 Volume 36, Number 7