With its circum-mediterranean distribution, the freshwater blenny Salaria fluviatilis is one of the most characteristic elements of the European freshwater fauna. As all other blennies worldwide are either marine or at least brackish water dwellers, much has been speculated about its ancestry and the way it could have colonized riverine and lacustrine water bodies surrounding the mediterranean sea. Studies have come up with several possible colonization scenarios, but ultimately failed to give a conclusive explanation yet. The only thing researchers seem to have agreed on lately is that the European freshwater-Salaria and their closest living relative, the brackish and marine S. pavo, most likely are monophyletic, that is having emerged from a single common ancestor, and entered freshwater habitats just once.
Genetic variation between most populations of S. fluviatilis is still comparatively low, which is striking given its wide distribution and the time these populations must have been separated from each other. A possible explanation for this could be the fact that S. fluviatilis can still acclimate to and successfully osmoregulate in full-strength seawater, leaving the option of marine dispersal. After all, some differentiation obviously has been going on, which led to the description of a blenny population from Lake Trichonis in western mainland Greece as a new species, Salaria economidisi, in 2004, which is hitherto only the second true freshwater blenny species described worldwide. Recent studies have shown that there might also be substantial genetic divergence between some populations from northern Africa (Morocco), Israel and Turkey, so we might see additional new species described in the future.
Also from a fishkeeper’s perspective, freshwater blennies (as much as their marine relatives) have a lot to offer. While their looks might appear unattractive to some (surely not me, though), it’s almost impossible to dislike their character. They show amazing behaviours, sometimes reminescent of gobies, then again worlds apart. While they lack a swim-bladder and consequently are bad swimmers, they’re nonetheless very active and curious (and they can swim if there’s something to swim for!). They soon know who’s feeding them and keep a close eye on you from behind the glass as soon as you enter the room. Food-wise, they consume about anything you throw at them, from small snails, fish, shrimps and all kinds of insect larvae, they’ll even pick on hair algae when they’re really hungry. They will soon learn to feed off your hand, but then again you don’t want such a pet fish, do you? Frozen foods pose no problem and it’s not impossible to get them to take a good quality pellet food, but it’s much more fun on both sides if they get the chance to hunt down the occasional Gammarus.
Although many authors have failed breeding freshwater-Salaria, it can be done. The problem is that the larvae go through a 3-4 week planktonic phase after hatching from eggs that the male guarded for about two weeks, so the key factor is providing the larvae with the right starter food. It appears mysterious why there has been not a single report of a hobbyist successfully rearing the larvae, as they are, though free-swimming, at about 5mm total length relatively large at hatching. Only in 2010, a team of Portuguese biologists published a paper on the successful raising of S. fluviatilis larvae, with the secret being nothing more than a diet of freshwater rotifers. This encouraged me to try breeding this species once again and hopefully there will be something to tell you about come next year.