The Sterlet – Acipenser ruthenus
The Sterlet can be described as a prehistoric fish which dates back to the dinosaurs. Its ancient ancestry is also quite clear when looking at its body form, looking completely alien in a pond when compared to other traditional pond fish.
The Sterlet, a close relative of the Sturgeon, derives from rivers that feed into the Black and Caspian seas and although it is a river fish, the Sterlet acclimatises well to a garden pond existence.
Instead of the usual scales as found on koi and goldfish, Sterlets are covered with armoured bony plates called scutes which are arranged the body in five rows.
The Sterlet also swims like no other fish, flexing the whole length of body into a series of lazy curves, moving in an ungainly, clumsy and ‘waggy’ fashion. There have even been instances where this weak swimmer has become trapped in blanketweed.
The Sterlet can have difficulty feeding in a pond for a number of reasons. Firstly the Sterlets protruding snout and downward facing mouth only really enable this fish to feed off the bottom, meaning that it is usually necessary to offer sinking pellets. This can lead on to a second problem, and that is one of competition. In a typical garden pond of mixed pond fish the frenzy of activity experienced at feeding time may well result in no food getting down to the Sterlets. They are a carnivorous fish, naturally feeding on crustacea and invertebrates in the water column or on the river bed. It uses a set of four fringed barbels protruding from its mouth to feel, sense and locate food items. It also uses these to locate sinking food pellets.
Tench – Tinca tinca
Every garden pond should have a tench. This sturdy, bottom feeding fish performs a perfect scavenging role, rooting around in the silt and sediment that may have accumulated over the seasons.
The tench’s natural colouration offers superb camouflage, with its dark brown-green olive skinned back blending extraordinarily well with the weedy depths which it loves and inhabits.
Tench are likely to be sold from pale-bottomed tanks or troughs where they can be easily viewed and selected. It is nearly impossible to see tench unless they are exhibited in such tanks and would otherwise be easily passed, unnoticed. In addition, tench are a shy fish, better suited to the more protective garden pond than exposed retail tanks that are designed for ease of viewing and netting.
Tench are more valuable in a pond for the work they do than for their ornamental appeal. Performing the role of the catfish, the tench has a slightly downturned mouth which is equipped with a small pair of sensory barbels for detecting food in the murky depths. No wonder it’s eyes are so small, it must hardly use them.
A naturally occurring though rare golden colour variant of the tench is available quite sporadically in aquatic shops. It is very similar in colour to golden orfe, with the contrast being that the golden tench prefer to inhabit the lower rather than the upper regions of the pond. Of course golden tench are more visible in a pond than their naturally coloured relatives and their popularity has a significant affect on their price and availability.
Although you should have no cause to touch or handle a tench, they have a reputation for being an extremely slimy fish. Their tiny, firmly-rooted scales are covered by what seems to be a liberal daubing of protective slippery mucus. Folklore maintains that the application of this ‘magical’ mucus to wounds or abrasions will help to heal the afflicted individual; hence its name as the Doctor Fish.