Even among those concerned with the defense of animals, it is not uncommon to be unaware of the plight of animals in fish farms, despite the significant harms animals may suffer in these places. A significant cause of the harms that can occur are the many diseases they can suffer, some of which are agonizing and lethal. Moreover, these diseases are often passed on to other animals living in the wild, harming them, too. Additionally, the antibiotics the animals are given can be harmful to them due to side effects, and can also negatively affect other animals in the wild.
In fish farms, many different animals are raised. We will examine here the diseases suffered by fishes and crustaceans. (See Diseases suffered by animals living on land farms to learn more about other ways animals suffer due to disease.)
As on land farms, in fish farms, there are very common threats to fishes’ health, including those caused by pathogens such as bacteria, viruses, and parasites. These can be found in very high concentrations in farms (even though they also occur in nature). As happens with land animals, the fact that the farms are so crowded makes it very easy for diseases to spread. Viral infections are particularly dangerous in this regard, since fishes who survive their infections can be carriers of the viruses and transmit them to non-infected animals, even if they present no symptoms.
In addition, the chemicals present in the animals’ environments can irritate their skin and mucus membranes, making them very susceptible to germs, similar to when they suffer from wounds.
Some bacteria commonly live in the digestive tracts of these fishes, without doing them any harm, and actually being beneficial in some cases. However, under conditions of stress, these bacteria can become harmful to the animals and actually be the cause of serious infections.
In addition, they are often given food that is not healthy. It makes them grow faster but causes health problems, such as lipid visceral degeneration, a condition from which many fishes suffer due to being fed products such as other fishes and crustaceans with a high density of fat and carbohydrates.
Fishes can suffer from diseases with various causes, including viruses, bacteria, fungi, protozoa, copepods or other fishes parasiting them. The most common bacteria attacking fishes in fish farms are those of the genera Vibrio, Aemonas, or Renibacterium, among others.1 One significant bacterial disease is enteric septicaemia, caused by the bacterium Edwardsiella ictaluri. Affecting catfish in particular, it is very common in the USA and in other parts of the world.
Among viruses that attack fishes in fish farms are those from the genera Birnaviridae, Rhabdoviridae, and Iridoviridae, which can all cause several serious conditions. For instance, infectious pancreatic necrosis affects salmonids and can be extremely lethal (affecting up to 90% of the animals in a given population). Birnaviridae can also be found among other animals such as basses and turbots. Another very common disease is the pring viraemia of carp, which affects several varieties of carps in various parts of the world, and is caused by a rhabdovirus. Another virus caused disease, which has very significant consequences for wild animals, is the eel rhabdovirus disease.
In addition to these hazardous viruses, these animals may suffer considerably due to parasites. Because of the conditions in fish farms and the high densities in which these animals are kept, parasites are extremely numerous and are not only a major threat to fishes’ health, but can also cause them great pain.2
For example, sea lice infections in salmon can make them suffer a great deal, although adult salmon may survive the infection. Juvenile salmon, on the other hand, are thin-skinned and are affected much worse by the action of sea lice;3 in fact, they often die due to these infections.
There are many different variables involving how a disease can spread in a population of fishes in a fish farm. How virulent the pathogen is that causes the disease is obviously one key factor, but there are others to take into account. They primarily include the animals’ resistance to disease, that is, their immune system conditions, as well as how stressed or weak they are. Certainly this can vary between different individuals, but there can be many general trends in fish farms. Also, the quality of the water and the environment in which the fishes are kept affects the impact of diseases. Crowded conditions, of course, foster an even swifter spread of disease.
Moreover, the problem with the spread of diseases in fish farms is that they are not caused only by pathogens that are native to the farms’ local areas; rather, many of them are caused by pathogens indigenous to other areas that have spread from certain regions to others. This is due to the conditions in fish farms that facilitate the spread of diseases so much that they extend across vast areas of the globe. As a result, animals living in the wild can eventually be infected. Because they may not have defenses against alien diseases, these animals are often harmed in massive ways.
The treatment of diseases with antibiotics and other drugs or chemicals also has an impact on animals living in the wild.
The following is a list of different diseases that fishes suffer from, both in nature and especially in fish farms.
|Bacterial kidney disease (Renibacterium salmoninarum)||Ceratomyxosis||Channel catfish virus disease|
|Eel rhabdovirus disease||Enteric redmouth||Enteric septicaemia of catfish (Edwardsiellosis)|
|Epizootic haematopoietic Necrosis||Epizootic ulcerative syndrome||Flexibacteriosis|
|Furunculosis||Gyrodactylosis (Gyrodactylus salaris)||Ichthyophthiriasis (White Spot)|
|Infectious haematopoietic necrosis||Infectious pancreatic necrosis||Infectious salmon anaemia|
|Koi herpesvirus disease||Lactococcosis|
|Oncorhynchus masou virus disease||Pancreas disease of salmon||Pasteurellosis|
|Pike fry rhabdovirus disease||Proliferative kidney disease||Red sea bream iridoviral disease|
|Sleeping disease of trout||Spring viraemia of carp||Streptococcicosis|
|Trout fry syndrome||Vibriosis|
|Viral erythrocytic necrosis disease||Viral haemorrhagic septicaemia||White sturgeon iridoviral disease|
Crustacea can also suffer from a wide range of diseases that can be massively fatal in farms.Viral infections that can affect crustacea include Iridoviridae, Reoviridae, and Picornaviridae, among others. These viruses can cause blindness and also affect behavior, which may become erratic. Infected animals may then die due to any of several reasons, including respiratory problems and problems with their osmoregulation (the regulation of the osmotic pressure of the fluids in their body to control their water content).4
They may also be infected by parasites, including amoeba5 and protozoa,6 such as those caused by Haplosporiodosis, as well as by fungi (for example, by the genera Fusarium or Lagenidium7). These parasites can cause a significant number of deaths among populations of these animals.
The White Spot Syndrome Baculovirus Complex is a very common condition among Penaeid shrimps.8 It has this name because infected animals show white stains on their shells. This disease can kill entire populations of these shrimps in a matter of days. It attacks animals from different species and is widespread today in countries surrounding the Pacific Ocean.
Giant tiger prawns suffer from a very contagious disease known as the Yellowhead disease, which can kill them in less than four days.9 When they suffer from this disease, the cephalothorax of infected shrimps turns yellow after a period of extensive feeding dramatically before they die.
Another widespread disease is Taura syndrome, which affects a species of shrimp whose individuals are commonly raised in several parts of the world. The disease spreads rapidly, and has already reached many parts of the world – cases have been recorded in places throughout Africa and Asia.
Another condition that has received much attention is Infectious Hypodermal and Hematopoietic Necrosis, which has affected many animals in the Pacific waters (both in fish factories and in the wild). This is a very lethal disease which can kill up to 90% of the animals in populations of western blue shrimps, as well as causing many other harms (including for instance severe malformations) among whiteleg shrimps.
Other diseases crustacea suffer from which can be fatal in farms include crayfish Plague (Aphanomyces astaci), tetrahedral baculovirus (Baculovirus penaei), spherical baculovirus (Penaeus monodon-type baculovirus), chitinolytic fungal disease (black mat syndrome) of crabs, and infectious hypodermal and haematopoietic necrosis (IHHNV), among others.
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1 Biosca, E. G.; Amaro, C.; Alcaide, E. & Garay, E. (1991), “First record of Vibrio vulnificus biotype 2 from diseased European eel”, Anguilla anguilla L.”, Journal of Fish Diseases, 14, pp. 103-109. Toranzo, A. E.; Magariños, B. & Romalde, J. L. (2005) “A review of the main bacterial fish diseases in mariculture systems”, Aquaculture, 246, p. 37.
2 See for instance: Glover, K. A.; Nilsen, F. & Skaala, O. (2004) “Individual variation in sea lice (Lepeophtheirus salmonis) infection on Atlantic salmon (Salmo salar)”, Aquaculture, 241, pp. 701-709; Johnson, S. C.; Treasurer J. W.; Bravo, S.; Nagasawa, K. & Kabata, Z. (2004) “A review of the impact of parasitic copepods on marine aquaculture”, Zoological Studies, 43, pp. 229-243; Revie, C. W.; Gettinby, G.; Treasurer, J. W.; Grant, A. N. & Reid, S. W. J. (2002) “Sea lice infestations on farmed Atlantic salmon in Scotland and the use of ectoparasitic treatments”, Veterinary Record, 151, pp. 753-757.
3 Morton, A.; Routledge, R.; Peet, C. & Ladwig, A. (2004) “Sea lice (Lepeophtheirus salmonis) infection rates on juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon in the nearshore marine environment of British Columbia, Canada”, Canadian Journal of Fisheries and Aquatic Sciences, 61, pp. 147-157.
4 Bonami, J. R. (1997) “Crustacean viral diseases: Recent developments”, Bulletin of the European Association of Fish Pathologhists, 17, pp. 188-190. Nash, M.; Nash, G.; Anderson, I. G. & Shariff, M. (1988) “A reo-like virus observed in the tiger prawn, Penaeus monodon Fabricius from Malaysia”, Journal of Fish Diseases, 11, pp. 531-53. Lightner, D. V. & Redman, R. M. (1993) “A putative iridovirus from the penaeid shrimp Protrachypene precipua Burkenroad (Crustacea: Decapoda)”, Journal of Invertebrate Pathology, 62, pp. 107-109.
5 Sawyer, T. K. (1976) “Two new crustacean hosts for the parasitic amoeba Paramoeba perniciosa”, Transactions American Microscopical Society, 95, p. 271.
6 Sawyer, T. K. & MacLean, S. A. (1978) “Some protozoan diseases of decapod crustaceans”, Marine Fisheries Review, 40, pp. 32-35.
7 Miller, J.D. & Fleming, L.C. (1983) “Fungi associated with an infestation of Pseudocarcinonemertes homari on Homarus americanus”, Transactions of the British Mycological Society, 80, pp. 9-12.
8 Chou, H.-Y.; Huang, C.-Y.; Wang, C.-H.; Chiang, H.-C. & Lo, C.-F. (1995) “Pathogenicity of a baculovirus infection causing white spot syndrome in cultured penaeid shrimp in Taiwan”, Diseases of Aquatic Organisms, 23, pp. 165-173. Corbel, V.; Zuprizal, Z.; Shi, C.; Huang, S.; Arcier, J.-M. & Bonami, J.-R. (2001) “Experimental infection of European crustaceans with white spot syndrome virus (WSSV)”, Journal of Fish Diseases, 24, pp. 377-382.