If you fish in Georgia regularly, you’ve probably noticed something changing. Maybe it’s the lake where you used to catch nice crucian carp, but now every fish that hits your net is the same silvery, deep-bodied clone. Or maybe it’s the river stretch where the barbel are suddenly scarce, replaced by a predator you never saw there five years ago.

You’re not imagining things. Georgia’s freshwater ecosystems are in the middle of an invasion, and the invaders are winning.

The Usual Suspects

Georgian researchers have documented 27 non-native fish species in our waters. Fifteen of them have established self-sustaining populations. At least three are causing what biologists politely call “catastrophic ecological disruption.” Let me introduce you to the worst offenders.

Prussian carp (Carassius gibelio) is the undisputed champion of Georgian invasion biology. This fish has a biological superpower that sounds like science fiction: gynogenesis. The females don’t need males of their own species to reproduce. They use sperm from other fish – common carp, crucian carp, anything in the carp family – purely to trigger egg development. The male’s DNA is discarded. Every offspring is an identical female clone of the mother.

What this means in practice is terrifying. A single Prussian carp female introduced to a lake can, within a few seasons, produce a population of thousands of genetically identical copies. Saghamo Lake, just a few kilometres from Paravani, is the textbook case. The lake’s native fish assemblage has been almost entirely replaced. If you fish Saghamo today, you’re catching Prussian carp. That’s it.

And they’re not staying in the lowlands. In October 2022, researchers found Prussian carp in the Tergi (Terek) River at 1,729 metres above sea level, in water fed by glacial melt. These high-altitude fish have developed strange physical adaptations – slower growth, disproportionately large heads – and they’re now competing directly with the endemic Terek trout for food. Climate change is warming alpine waters just enough to open the door for these invaders.

Sharpbelly (Hemiculter leucisculus) is a different kind of problem. It’s a small, silvery Asian cyprinid that looks like bait and acts like a plague. First detected in the Alazani River in 2020, it has already colonized Bazaleti Lake and Sioni Reservoir. It has no value to anglers, no value to commercial fishermen, and no natural predators in its new range.

The most frustrating part? Its spread is almost certainly caused by anglers. Sharpbelly are small enough to be accidentally scooped up as live bait in one water body and then dumped, alive and well, into another. Every bucket of unused bait poured into a lake at the end of a session could be seeding the next invasion.

Zander (Sander lucioperca) is the newest troublemaker on the block. A sharp-toothed predator native to eastern Europe, zander were introduced to the Algeti River system around 2022 – illegally, by anglers who wanted a new sport fish. The dam on the Algeti River has fragmented the ecosystem in a way that perfectly suits zander. The still reservoir waters favour their visual hunting style, while the native cyprinids downstream evolved for fast currents and have no defence against a predator they never encountered in their evolutionary history. In just a couple of years, zander have devastated native fish densities in the middle and lower reaches.

How Did We Get Here?

During the Soviet era, the state introduced “Chinese carps” – grass carp, silver carp, and bighead carp – as a deliberate aquaculture strategy. The idea was to control aquatic weeds and boost cheap protein production. These fish rarely breed naturally in Georgian rivers because they need massive, turbid, unimpeded flows to keep their semi-buoyant eggs suspended. As long as the hatchery trucks kept arriving, the system was stable.

Then the Soviet Union collapsed. The hatchery network collapsed with it. But the fish, of course, were already in the water.

The modern problem is different. It’s driven by what researchers call “vigilante stocking.” Individual anglers, well-meaning or otherwise, catch fish in one water body and release them in another. Prussian carp. Sharpbelly. Zander. European perch in Lisi and Turtle lakes. The motivations vary – some want a new sport fishery, some just dump unused bait – but the result is the same. Species jump across watershed boundaries that they could never cross on their own, and the ecosystems on the receiving end have no time to adapt.

The Regulatory Vacuum

Here’s the uncomfortable truth: Georgia has no official catalogue of invasive alien species. No legally binding blacklist. No ban on importing specific problem fish. The National Environmental Agency issues stocking licenses based on long-term ecological plans, but post-licensing monitoring is essentially nonexistent.

This means there is no enforcement mechanism to stop someone from catching a bucket of Prussian carp in Saghamo and dumping them into a pristine alpine lake. None. The law has nothing to say about it.

What You Can Actually Do

This is not one of those blog posts that tells you to write to your MP. Here are practical things that matter:

  1. Never move live fish between water bodies. Not bait. Not catch. Not “just one interesting specimen.” The sharpbelly in Sioni Reservoir got there because someone ignored this rule.

  2. Don’t release Prussian carp. Unlike most fish in Georgia, there is no ethical argument for catch and release here. Every Prussian carp you remove is one less competitor for native khramulya, barbel, and trout.

  3. If you see something weird, say something. Zander in the Algeti were noticed by anglers before researchers confirmed them. Your observations matter. Report unusual catches.

  4. Clean your gear between trips. Invasive fish eggs and larvae can hitchhike on nets, boots, and waders. A quick rinse isn’t enough; dry your gear completely between different water bodies.

The fish in Georgia’s waters are a mix of ancient natives, Soviet-era introductions, and modern invaders. Some of that is permanent. The Kura barbel and the Prussian carp now share the Mtkvari, and that’s not changing. But the speed of the invasion – sharpbelly spreading to three major water bodies in four years, zander establishing a breeding population in two – is what should worry every angler in this country.

The lakes and rivers you fish today won’t be the same in ten years. Whether they’re better or worse depends partly on what we do, and mostly on what we stop doing.

Image Guide

Image 1 (hero): A split comparison photo. Left side: a clean, natural-looking Georgian lake with native vegetation. Right side: the same type of scene but visibly degraded, murky water with a dead fish on the shore. Alternatively, a close-up of a Prussian carp held in an angler’s hand, with the fish clearly showing its distinctive deep, silver body shape.

Image 2 (inline, after “The Usual Suspects” heading): A side-by-side identification chart showing Prussian carp vs Common carp vs Crucian carp, with arrows pointing to the key distinguishing features (body depth, scale size, colour). Clean white background, clear labels.

Image 3 (inline, with “Sharpbelly” paragraph): A macro close-up of sharpbelly against a neutral background, showing its small size (include a coin or ruler for scale). The fish should be freshly caught, still showing its silvery iridescence.