 |
|
Glassfish
Warning! Periodically, glassfish are sold which have been injected with brightly coloured dyes. Besides being very cruel, this process weakens the fish and may make it more susceptible to disease. Please don’t buy these dyed fish.
Glassfish are small perch-like fish which are found in salt and brackish water around the coastline of tropical Asia and Australia. They are laterally compressed perch-like fishes that are remarkable for their transparent bodies. Several species are offered to aquarists, but actually identifying these species is rather difficult. At least three species in the genus Parambassis that are traded fairly regularly as the ‘common glassfish’ or ‘Indian glassfish’, but of these Parambassis ranga appears to be the most frequently seen.
Glassfish are not easy to keep for several reasons. Firstly, they are very picky about their food, and while they may sometimes take dried foods this is rarely the case with newly imported specimens, and even after months in captivity most will only take live or frozen invertebrate foods. Frozen bloodworms, mosquito larvae, and lobster eggs are readily eaten, and once settled down you can try a variety of other small, meaty foods such as shrimp eggs and small pieces of shrimp or white fish.
The second problem is that none of the glassfish is really hardy in the sense of being tolerant of rapid changes in water chemistry or poor filtration. When introduced into immature aquaria they often sicken and die rather quickly, although the aquarist may be warned that something is wrong when these normally silvery or transperant fish take on a milky hue.
Finally, it is debatable whether or not these are truly brackish water fish. In the wild the species offered to aquarists normally inhabit fresh rather than salty water, but by the time these fish arrive in your local tropical fish shop they will invariably have been maintained in slightly brackish water for several weeks. At least some species appear to do well in slightly brackish water, and most aquarium books recommend keeping them in aquaria with a specific gravity of around 1.002 to 1.005. Even so, it is as well to be aware of the fact that these fish actually prefer neutral, soft to moderately hard fresh water. Glassfishes are sensitive to low temperatures, and will need to be kept at around 25° C (75° F) outside of breeding.
Otherwise these fish do not pose any major problems. Most are relatively small (typically around 4 to 8 cm in length), completely peaceful, schooling fish. They do best in planted tanks and prefer a mix of bright and shady spots and enjoy a strong water current. Good tankmates include gobies, peaceful livebearers, and halfbeaks. Some species have bred in captivity. Raising the temperature up to 28° C (84° F) and allowing the tank to get some natural sunlight in the morning appear to be most reliable triggers. The eggs are scattered among plants, and although generally ignored by the parents it is probably best to remove them just in case. The eggs are prone to becoming fungused, but this can be prevented by use of an antifungicide. Raising the fry is difficult because they are very small and can only take infusoria at first.
The most commonly seen glassfish are Parambassis ranga, Parambassis lala, and Parambassis siamensis, all of which are offered simply as ‘glassfish’. In breeding condition, male Parambassis lala have blue-white edges to their anal and dorsal fins while those of Parambassis ranga and Parambassis siamensis are off-white or grey. Otherwise, all these fish are wonderfully transparent fish and tricky to tell apart. These best indicator is body shape and markings. Parambassis siamensis have rather elongate bodies (they are about three times long as they are deep) while Parambassis lala and Parambassis ranga are much more diamond-shaped (about twice as long as they are deep). Parambassis lala and Parambassis ranga can be distinguished by their markings: Parambassis lala have three vertical bands running down the flanks while Parambassis ranga has at most a single dark spot behind the eye.
A giant among glassfish is Parambassis wolffii, which can easily reach a length of 20 cm (8 inches) or so, though once fully grown is no longer transparent but a rather plain steely-grey in colour. This is a very rarely traded species: in twenty years I have only ever seen a single adult of this species offered for sale, though juveniles may get mixed up in batches of common glassfish rather more frequently. Another large glassfish is the hump-headed glassfish Parambassis pulcinella. This species was unknown in the hobby until very recently, but it is now exported from Thailand and Burma fairly frequently. Both Parambassis wolffii and Parambassis pulcinella are unquestionably freshwater fish and should not be kept in brackish water aquaria.
Another very rare glassfish is the filament glassfish Gymnochanda filamentosa, similar in size and habit to the common glassfish but with the males possessing greatly extended anal and dorsal fin rays. They need soft, acidic water conditions similar to those of discus and tetras. Obviously this fish is unsuitable for brackish water aquaria.