Spain's Unwelcome Fish Guests

Buscalo November 2006

The angler’s latest challenge in Spain is not to clutch the largest carp or barbel but to bag the most number of different fish. As each year unfolds there are tens of new fish species waiting to be caught and then identified. This does not mean that Spanish fish are evolving into new species faster here than elsewhere.  But that invasive fish are arriving more frequently than before.

Believe it or not piranhas are now on the loose. Some have turned up on the River Turia near València exceeding 1kg in weight. It was introduced presumably to eat sunfish! Next time you decide to dispose of those garden pond fish, please think again.

Where do they come from? Roach, rudd and bream were imported by French and German anglers, as live bait in order to attract huge catfish (siluro) from the River Ebro in north east Spain during the 1970’s.  

In this age of globalisation you stand as much chance of bagging an exotic fish species, from Spain’s rivers and reservoirs, as you do a native shad.

The small sunfish (perca sol - pumpkinseed), which is a member of the Bluegill family, have come from Mexico. They arrived in small numbers but have multiplied into millions thanks to Spain’s welcoming aquatic conditions and year-round, favourable climate.

Fish don’t have to be big to cause havoc. Numbers count more in nature than size. Sunfish average just 0.05kg in weight but have caused immense damage to native Spanish fish stocks through competition for food and habitat.  Its young grow much quicker than native fish fry and therefore deny food to competing species. Juvenile sunfish eat fish eggs of every native fish species by the tonne.

Buscalo readers will be familiar with the story of a neighbour, but never themselves, releasing goldfish and other tropical species into local irrigation channels when their own garden pond has become overcrowded.
If brown trout can thrive in a drain or ditch – trout are very sensitive to pollution and low oxygen levels, then so can most other fish.

It’s possible for just a handful of invasive fish to conquer the whole of Spain in two decades. There are two reasons. Spain’s extensive system of irrigation channels and canals connect up a region’s main waterways, rivers and reservoirs provide an eco highway along which fish can colonise new territories. Constant spawning conditions, in a warm climate boost numbers.

All release of non-native fish into Spanish continental waters is considered illegal, unless the government has given permission. And the government has made errors of judgement.

Lousiana Red crayfish from the United States were introduced as a cash crop, under licence in the 1970’s but were found to be too bitter for the Spanish palette. From a single point of distribution, in Andalusia it has spread more than 700km in less than five years. It has displaced the native Spanish crayfish from lakes and rivers and it eats the stems of young rice plants, a huge commercial crop in València and Catalonia.

Andalusia has created a plan for the control of invasive fish species. It’s called Plan Andaluz Para el Control de Especies Exóticas Invasoras.  A decision has been taken to eradicate carp in the Reserva Natural de Laguna de Zóñar by the environment agency (Medio Ambiente de Andalucía), in collaboration with the Córdoba University.

In this instance common carp have been thought harmful to the local habitat because they are believed to have decimated submerged and semi-submerged aquatic vegetation. This was creating serious problems for a site recognised as of regional and international importance for bird life.

Rain fell recently: eventually filling everyone’s buckets. Rivers that had ran dry for the last nine months (barrancos) will now be re-colonised by barbel, a migratory fish and carp – a very adaptable fish.

Nature follows a cycle of events. You will be surprised how quickly the environment recovers. During dry periods, large carp hold up in drains and ditches off the main channel. And wait for rain.

However natural water supplies will be put under even greater pressure when Murcia plans to kick start the property market by planning construction of four major new large towns.

This economic initiative is unsustainable and it will result in further degradation of the environment. Investment in de-salinisation plant and modernisation of fifty year old irrigation techniques is expensive. For example, València’s ground water has been sufficient for its own needs but is polluted through industrial neglect.

The Spanish economy’s claim on natural resources will produce, in the near future, further dry river beds for longer periods of time.  There is enough water for everybody.

Tips for catching piranhas include leaving your toes in the water.

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