If you want to push the boundaries of the reef, we introduce you to the neon blue eye Pseudomugil cyanodorsalis. Pseudomugil gertrudae and furcatus, a genus of primarily freshwater fish native to Australia and New Guinea, are the two species normally found in tropical planted tanks with their delicate blue eyes, double back, and the flare of male fins.
As you learn more about Pseudomugil, you can find and keep the beautiful P. paskai or P. ivantsoffi. However, if you go deeper you will find that some of these members of the rainbow fish family go into brackish water in the wild and beyond.
“Cyanodorsalis are essentially estuarine fish,” photographer and rainbow fish expert Gunther Schmida told Reefbuilders. “They swim in the open water of canals or between mangrove roots in completely marine environments and in low salinity conditions.”
“I collected them at night at low tide in tiny, shallow pools in mangrove areas. I also kept them in self-sufficient small schools in 180-liter tanks with a salt content of 30-50% seawater. They survive in pure fresh water for a few weeks, but not in the long term. Although I have never kept her in full sea water, I cannot understand why that would be a problem. They are great little fish to hold, but they do need some space to jump around. You are incredibly active. “
We’ve explored the species further and sure enough. The Neon Blue Eye lives in salt water and occurs naturally in salt contents of up to 40 per thousand. Our reef tanks typically run between 33 and 35ppm, so this tiny rainbow fish can and should live pretty happily in full strength seawater in captivity, as it survives this and more as part of its life cycle in the wild.
They are a tiny species and grow to only 3.5 cm. The natural range extends from Broome in Western Australia to Darwin in the Northern Territory.
However, this does not mean that if we find products for sale we can toss them into our mixed reefs and they will be fine. Their tiny size will put them on the menu of hawks, anemones, and even some wrasse, and our reef crest river patterns are a far cry from the calm, tangled backwaters of a mangrove swamp. There is a risk of them being drawn into drive heads and they can even fit through bulkhead screens and weir combs.
Instead, the demands of this delicate species scream for shallow saltwater lagoon, live mangroves, and even a tidal system if you have the know-how. Set the scene with a bed of fine sand or a sea mud substrate with vertical roots and macro algae and bright, weak Kelvin light with a slow, steady flow.
This other type of marine tank could then also be used to care for other small, sensitive species such as Red Spot Cardinalfish, Pipefish or Scooter Blennies, which also do poorly and can compete for food in the daily rough and tumble of a mixed reef.
Or keep it authentic and set up a North Australian mangrove biotope, a true home for that special little saltwater fish.
Image courtesy of the copyright holder Gunther Schmida.