Stone Loach a Secretive Existance

 

If you asked the general public what a Stone Loach was I would wager most have never heard of one, in fact I would guess even a lot of wildlife enthusiasts have never heard of one, or couldn't identify it. As with lots of aquatic species this is perhaps best described as out of sight out of mind. This is a secretive species of fish which goes under the radar, too small to be caught regularly by fishermen and out of sight of most naturalists. Further to this it has a largely nocturnal and benthic existence amongst the stones and gravels on the riverbed, often laying partially buried, making it even more difficult to spot.

This is a small species although larger individuals can top 20cm in length, it is also well distributed across most of Europe and is locally common around North Yorkshire and parts of East Yorkshire. It has a prerequisite for well oxygenated water, meaning it is almost always recorded in streams or close to where streams run into larger waterbodies. 

Larval Stone Loach are benthic as with the adults, having a preference for slightly slacker sections of water often with a more sandy base. As the develop they slowly move towards more gravelly substrata with faster flows. This shows the importance of habitat structure and how different life stages have different habitat requirements. This species is short lived with a maximum lifespan of around 5 years. The diet is largely made up invertebrates, particularly gammarid shrimps and chironomid larvae, in this species. Spawning occurs largely over gravels and sands, although occasionally vegetation is used. The productivity of the watercourse influences the amount of spawning events per year, with spawning occurring more than once a year in more productive areas. 

Stone Loach are good indicators of water quality, whilst they can persist with moderate organic pollution, they are highly intolerant of heavy metal pollution, chemical pollution and low oxygen levels. It is therefore clear to see that discharging of sewage and similar practices from agriculture and water companies could quickly have negative impacts on populations of this fish.