According to data available from the FAO, global aquaculture produced 65.2 million tonnes of products, compared to 67.2 million tonnes caught by fishing boats. The European Union is the world's third largest fishery and aquaculture producer (4.4 per cent), after China and Peru. Spain is the EU member state with the highest production (21.6 per cent of total), ranking 21 in the world as a producer of seafood products, be it aquaculture or fisheries. Fish production in our country is estimated at 1.3 million tonnes, with a coverage rate of 60 per cent, resulting in the need to rely on imports to supply domestic demands.
Such is the importance of our country in this sector, that on the 1 July, 2008, the headquarters of the Community Control Agency for fishing moved to the city of Vigo (Pontevedra).
After four decades of continuous growth, aquaculture make-up half of aquatic products consumed by humanity in 2010. This high growth sector plays an important role in the European diet, as the average annual consumption of fish is 21.4 kg per person, compared to the world average of 16.1 kg per person.
The aim of this work is to study one of the main residues found in aquaculture, malachite green. Until recently, it was frequently used as a disinfectant, especially in salmon farms, and was considered irreplaceable, but later antiseptic and antiparasitic effects were discovered.
In the last decades, misused substances have posed a serious risk to human health. The technical reasons that its use is promoted lies in the improvement of animal husbandry production rates, increasing the economic benefit for producers. Given this, in 1989 was approved the National Plan of Waste Inspection (PNIR), monitoring of the detention of waste in the production chain of animals.
Uses of malachite green
Malachite green (MG) is a basic dye soluble in water; for the treatment of fish and their eggs, it is used in preventive and curative baths as one component (only MG in various concentrations), or multi-component baths (in combination with bright green, crystal violet, formaldehyde, etc..) in the following infections:
• Fungal infections: Parasitic Saprolegnia, The effects of fungicides have been known since 1930, mycosis produced great economic losses, not only by decreasing the amount of product, but due to poor conservation of infected individuals. Saprolegnia does not survive in environments with a high salt concentration, therefore, it can be seen as a freshwater disease.
• Parasitic infections: Ichthyophthirius multifiliis (protozoan) freshwater fish parasite, known as white spot disease, affecting the animal's skin, producing a visible white cyst, which explodes when ripe releasing new parasites that infect other specimens.
• Bacterial infections: Flavobacteria located in the gills, skin and muscles of various freshwater fish.
MG is still very popular in aquaculture plants since it's a potent antifungal and antiparasitic compound, it has a low cost, high efficiency and there are a lack of alternative products with similar benefits.
Symptoms and health risks
Scientific evidence indicates that MG, in particular its reduced form leucomalachite (LMG), is absorbed and accumulated in the liver, kidney, muscle and other tissues of fish, persisting for long periods of time, depending on: water quality, concentration, duration of the bath, temperature, pH and waiting time.
MG produces negative properties with acute toxicity in fish, with the difficulty that the lethal concentrations and the concentrations recommended for therapeutic treatments are sometimes very close. The typical clinical symptoms they cause are: nervousness, uncoordinated movements of fish in tanks, swimming in the upper third of the surface, apathy, agony and death. Its pathology in fish, caused by malachite green poisoning, is characterised by the greenish colour of the skin, gills are swollen with excessive mucus, discoloured, showing the dilated veins, muscle tissue and internal organs show a slightly greenish colour.
Treatment of eggs to reduce fungal infection, cause malformations, mitotic defects and chromosome breakage.
Currently only be used in aquaria of ornamental fish, not intended for consumption since the residues in aquatic products have been causing high toxicity in mammals, with effects including: carcinogenic, mutagenic, teratogenic toxicity, respiratory and chromosomal fractures, which pose a threat to human health.
The scientific literature gives us little information on the adverse effects of MG on the environment, but we must not forget its persistence in the aquatic environment, which is estimated at over 80 days.
Regulation 2377/90 of the EU imposes a ban on the use of malachite green in all categories of edible fish processing, including fish eggs, this ban came into force on January 1, 2000. In 2002, the European Commission adopted the Decision No 2002/657, which refers to the minimum required detention limit for analytical methods (MRPL) for the use of certain substances that were never approved for use in member states or are explicitly prohibited. The MRPL for malachite green is 2 mg per kg.
Material and results: We compared the number of samples collected in Galicia, Spain and the EU, during the years 2005-2007, on the residues analysed in aquaculture (A1, A3, A5, A6, B1, B2a, B3a, B3c, B3d, B3e).
B3e (dyes, triphenylmethane derivatives), namely malachite green, makes up the majority of residues, appearing in 76 per cent and 56 per cent of the results, in the EU and Spain, respectively.
EU data that detected malachite green in aquaculture products were in 2002 (112), 2003 (81), 2004 (57). The years 2005 to 2007 are reflected in the following table. In Galicia, the matrix studied was trout muscle collected from farms.
In parallel were studied the assessments by ANFACO
(accredited laboratory) in the period between 2005 and 2008. With a total of 1,421 samples, 77 per cent substances being in Annex IV of Regulation 2377/90 and the remaining 23 per cent being the search for derivatives of triphenylmethane. 16 results were NC (not compliant), 15 belonging to group 1 samples from Chinese shrimp (11 SEM, AOZ 3), Peru (1 chloramphenicol) and MG detected in pangasius fillets from Vietnam.
For the production and growth to be optimal, the aquatic animal husbandry sector should have excellent sanitary conditions, have high quality feed and obtain veterinary drugs approved for the sector, their limited availability being one of the main problems in aquaculture.
Develop new methods of prevention, such as vaccines, improved nutritional quality, selection of disease resistant species. It must ensure the protection of consumers and recognise the health benefits of seafood. Keep to scientific knowledge and the precautionary principle to ensure that seafood, both domestic and imported, should be safe for consumers. The EU has almost 2 per cent non-compliant results of waste in aquaculture, much lower than other countries. The import controls were more present (Chile, Vietnam) on MG. We need a guarantee that the waste import controls are adequate and sufficient, in order to avoid unfair competition and market entry of products that do not meet legal standards.
Increase its control, unlike in Galicia where it has been absent in trout farms for years, due to it being focused on areas such as antibacterial and antiparasitical residues being present in the offspring of numerous species. Aquaculture producers are launching Health Defence Groups with the essential presence of veterinarians, which aim to raise sanitary standards through the establishment and implementation of joint programs of prophylaxis, the fight against animal diseases and improving hygiene conditions, which will allow production levels and improve the health of fish.