Since I am now unable to collect the Danio margaritatus, I will be moving the Pseudosphromenus dayi to this aquarium instead. This anabantoid comes from Kerala, the most south-western Indian state where air temperatures range from 15 to 36 °C, which I assume corresponds to water temperature of 16 to 34 °C. The fish have been found in fresh and brackish water, usually in lentic conditions, and may be very common in Chalakkudy River, Muvattupuzha River and Periyar River. There are some claims that this species can also be found in south-east Asia, but this is very likely to be a mistake caused by a mislabelled P. cupanus holotype.
As with other Osphronemidae, P. dayi possesses a labyrinth organ as well as gills, which allows it to breath air instead of extracting oxygen from the water as most other fish do. The labyrinth organ is located in the gills, at the first gill arch. I have read of research done into the breathing of Betta splendens, another labyrinth fish, where results showed that without access to air, the fish suffocated, so it is safe to assume that fish which have a labyrinth organ do require access to air at all times.
Apparently, the fish can grow up to 75 mm, although one of my females is currently at 30 – 35 mm and the male is around 35 mm at, by my estimate, at least one year of age. Fish are normally measured nose to base of tail for consistency, as tails can vary in length between individuals; with the tails included, the same female is around 45 mm and the males is close to 50 – 55 mm.
Mature males of the species have more orange throats, considerably elongated and pointier dorsal and caudal fins, and slightly elongated anal fin compared to females. Juveniles are almost impossible to sex unless the males’ fins have already started growing longer and I have found that the orange throat is usually more noticeable when the fish are ready to breed.
These gouramis are not shy, but do require plenty of plants as they spend most of their time under leaves. I currently have three of these fish in a 420 litre aquarium, where each one has taken up residence in a specific group of plants. One female has chosen a large Anubias barteri (spending most of her time under one of the broad leaves or swimming thought the roots), the other female has taken up residence in some plants which have floated to the surface, while the male lives in a patch of Cryptocoryne wendtii ‘brown’ (I often see him wrapped around one of the leaves). Flow does not seem to matter much to them as the females are both in areas where there is almost none, while the male spends much of his time about 15 cm away from a circulation pump, which is pointing directly at him. They are not strong swimmers, so I would say that a densely planted aquarium or one with low-flow areas is compulsory. The aquarium is 60 cm tall, but all three fish spend their most of their time either within 15-20 cm of the bottom or inside floating plant clumps, with the exception of feeding times, when they happily come out into the open.
As with many other gouramis, P. dayi is a surface feeder and their natural diet includes insect larvae. In an aquarium environment, they readily take all prepared and live foods of appropriate size. They are a slow feeder which takes its time to come out for the food, so it is important to make sure that they receive their portion of the food, especially if they are kept with fish which are known to be greedy for food.
P. dayi are compatible with most peaceful, community species, with the usual exception of other labyrinth fish and those which are big enough to eat them. Because they are a slow species with a flowing tail, they will make prime subjects for abuse by fin-nipping species, so it is best to avoid those.
The species breeds in pairs, with the male building a bubble nest inside a cave or under some leaves. The female lays approximately 200 to 300 eggs, which sink to the bottom and are collected by both parents before being spat into the nest. The eggs are guarded by the male and will usually hatch within 24 – 36 hours. After a few days, the fry use up their yolks and become free swimming.
P. dayi are currently classed as vulnerable by the IUCN, so it is worth looking for aquarium bred specimens over wild caught ones. Deforestation and agricultural activities, man-made pollution, mining and destructive fishing are the main threats to their habitat.
After more than a few hours of searching, I finally located the journal that the species was originally described in on Google books, but I am unable to find somewhere that I can download it from. For reference, the species was originally described as Polyacanthus cupanus dayi by W. Köhler in 1908. The paper, Untersuchungen über das Schaumnest und den Schaumnestbau der Osphromeniden, was published in Blätter für Aquarien- und Terrarien-Kunde, Stuttgart, volume 19 (pages 392-396). If anyone has a copy of it, please let me know as I am interested in reading it.