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TENTATIVE SOLUTIONS TO AN ALIEN SPECIES INVASION FROM

AQUARIUM AQUACULTURE: DEVELOPING VIABLE INDUSTRIES TOEXPLOIT AND CONTROLPTERYGOPLICHTHYS MULTIRADIATUS

HANCOCK 1828 IN MEXICO.

Carlos Martinez Palacios*1, Carmen Aguilar Valdez, Philip Scott2, Lindsay Ross3

1Lab de Acuicultura, IIAF, UMSNH, Michoacn, Mxico. fobospalacios@hotmail.com2Univerisdade Santa Ursula, Rio de Janeiro, Brazil

3Institute of Aquaculture, University of Stirling, UK.

Introduction

The Rio Balsas catchment in west-central Mxico covers an area comprising 6 states ofthe republic and a number of important dams have been constructed along its length. The

largest of these, the Adolfo Lopez Mateos dam (el Infiernillo) covers an area of

2,475km-2

. It was constructed in 1961 and quickly became one of the largest Tilapia

fisheries in Latin America with many families dependent upon its productivity.

The South American sail fin catfish Pterygoplichthys multiradiatus was released

accidentally into the upper tributaries of the Rio Balsas catchment, probably fromaquaculture for the aquarium trade. The species was first found in the natural

environment in 1995 but appeared in the dam in 2000/2001. At that time it was a relative

rarity and even the subject of some competition between fishermen to land a specimen.

The tilapia fishery has declined in recent years for a number of reasons but one of the

major changes has been the explosion of the population of Pterygoplichthys

multiradiatuswhich has increased to such an extent that 80% of every catch now

consists of this alien species.

There is no tradition of utilization of

this fish in the region and hence, up to

now the species is considered as a by-catch, albeit a massive one, from what

is essentially a tilapia fishery.

Concern has also grown because thefish damages gill nets and the spiny

scales and fins make the animal

difficult to remove from the mesh, as

well as being painful to handle. Thebody of this species has a large head

and small tail (Fig. 1) and so therecoverable flesh quantity at about

28% is relatively low when compared

to many other species (Fig. 2).

Possible solutions

One ideal solution to this problemwould be to remove the species from

the natural environment (Mendoza et

al.,2007) although there is littleprospect of achieving this in the short to medium term. A better immediate term solution

is to intensively exploit products from this new fishery and here we describe a series of

trials, ongoing during 2007, to investigate this opportunity.

Fresh product: This and similar species are consumed fresh in Brazil, Colombia and

other countries. This fishing activity and natural predation contribute to keeping the

populations under control. In fact, in parts of Brazil the fishery is now controlled to

avoid over-exploitation. Preliminary trials in Mexico show that with proper traininghigh quality fillets can be recovered from the species (Fig. 3). Simple preparation

Fig. 1. Adult specimen of Pterygoplichthys

multiradiatus.

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250

Fillet weight (g)

Totalbodyweight(g)

Fig. 2. Flesh yield of Pterygoplichthys

multiradiatus.

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has resulted in a product which has high

nutritional value and which has been wellaccepted in taste trials with the local

communities.

Smoked product: Trials with artisanalsmokers have been very successful. The

smoked tail fillets have a good flavour

and quality and also give a product with

added value. The main impediment to thisapproach is in developing a market.

Silage: Once the flesh has been recovered

from the species, the head, guts and skin can be ensiled to produce a proteinaceous

product for addition to animal feeds. Preliminary trials at the kilogram scale have

shown that a stable, semi-moist product can be produced from relativelyunpromising ingredients.

Soap manufacture: A by-product from silage manufacture is a layer of oil on top of

the mixture. This can be skimmed off and used, either alone or in combination withwaste cooking oil, to prepare soap for local use or sale.

Enzyme extraction: The alimentary tract of these fish contains a range of powerful

enzymes for dealing with the detritus on which they principally feed. Theseenzymes can be extracted, concentrated, freeze dried and used for digestion of

sewage and polluted waters to reduce environmental impacts.

Fish meal production: There have been several proposals to develop a fish meal

industry based on this fishery. However, this is not a viable economic proposition

because the fishery is not sufficient to provide the source material for even theminimum sized industrial fish meal plant. Current estimates show that a fish meal

yield of only 8 tonnes per day could be expected if collection and management were

optimized. Artisanal fish meal operations almost always result in a very poor

quality product and also have no future in this situation.

State and Governmental involvementAs there is no established use for the species the current practice is to simply discard the

product. This has environmental consequences as well as being a waste of a resource. As

already mentioned, exploitation is the most probable short to medium term solution tothe problem. The problem has become so serious that the national biodiversity agency

(CONABIO) has expressed concern and National and State governments have moved to

develop projects to resolve the issue. This involves not only technical research todevelop exploitation methods but also essential work with communities to increase

awareness and to raise the value of this species so as to promote its exploitation. An

important aspect of this will be the development of markets and a serious programme ofcommercialization of any viable products.

Conclusions

This paper shows some of the alternatives for intensive exploitation of an invasive alien

species. We suggest that these methods are the best approach to managing the problemof population explosion of this species but the success of such a project requires not only

technical solutions but also the financial and political support of state and localgovernment.

References:Mendoza, R., Contreras, S., Ramirez, C., Koleff, P., Alvarez, P. and Aguilar, V. Los peces Diablo:

Especies invasoras de alto impacto. Biodiversitas. 70: 1-5.

Fig. 3. The fresh product tastes good!