Fish and Marine Invertebrates: Health, Disease and Physiology


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See also:

Book reviews: Fish

Animal Care and Behaviour: Fish


City fish take in antidepressants

Trout near Montreal may be affected by antidepressants in sewage

source: New Scientist vol 209 no 2797, January 29 2011 p5

Trout near Montreal, Canada, may be affected by antidepressants in sewage from the city. University of Montreal's Sebastien Sauve screened the muscles, livers and brains of trout exposed to sewage that came from Montreal, mixed with water from the St Lawrence seaway. The antidepressants found in the trout included Prozac. Sauve fears that the drugs could have an effect on fish behaviour in the long term.


Accidental electroshock of fish in a recirculation facility

Effect of short, accidental electrical exposure on fish in a research facility

source D.J. Pasnik et al
Veterinary Record vol 153 no 18, November 1 2003
starts p 562, 3 pages long

Fish can be hit by lightning, or affected by faulty electrical equipment. This study shows the effects of a brief, accidental exposure on yellow perch, kept in a lab setting. The fish were all found lying on the tank bottom, and their bodies were distorted. The system was repaired, but the fish were subsequently not able to eat unless fed by hand. Ten weeks after the event, they were euthanased. The fish were examined and found to have luxations and vertebral fractures. There were also haemorrhages in the fishes' dorsal musculatures. These injuries were caused by the accidental shock, though the equipment was designed to cut out after some 0.025 seconds. The spinal deformities seen in these fish appear to be the result of severe contractions of white muscles. The vertebral column absorbs stresses, and fractures or compresses. These fish did not show signs of burns, which is to be expected, since they were immersed in water. Electrocuted fish can be permanently deformed after electrical exposure, and this can lead to 100% mortality rates. Nerve, tissue, and muscle damage can result from exposure to electricity. Fertility, growth and stamina can be affected, and changes in the blood chemistry of electrocuted fish have also been noted, including higher levels of cortisol and glucose.


Efficacy of bronopol against infection of rainbow trout (Oncorhynchus mykiss) with the fungus Saprolegnia species

Bronopol found effective against Sarolengnia fungus infection in brown trout

source: E Branson
Veterinary Record vol 151 no18, November 2 2002
starts p539, 3 pages long

Saprolegnia fungi are probably the pathogenic fungus species most commonly affecting fresh water fish. The fungi tend to affect fish that are already weakened by disease, injury or malnutrition. Handling may cause injury to skin, which can lead to infection, which gives the fish the appearance of having cotton wool patches. Malachite green, a teratogen and carcinogen, is traditionally used to treat salmonids, but no licensed treatment for UK fish farmers exists.

The trial sought to assess how useful bronopol could be in tackling a natural Saprolenia infection affecting rainbow trout. Bronopol is an enzyme inhibitor, and the formulation used came from Novartis Animal Vaccines. Eighty broodstock were used in the trial, carried out after handling to strip their eggs. The group was spilt into four groups of 20 fish each, moved to separate raceways from a common raceway. Two groups were treated with bronopol at 20mg/litre for 30 minutes per day, and two were given a placebo over 15 days.

The fish receiving bronopol showed zero infection level by the end of the trial, compared with 40% for one group and 70% for the other at the start, while the untreated fish showed an increased in infection from 35% to 55% in one group, and 45% to 74% in the other. Some infections in the untreated fish may have come from river water used in the raceways during the trial, while the treated fish were protected against reinfection. No adverse reactions to bronopol were apparent. 


Flavobacterium columnare (Flexibacter columnnaris) associated with severe gill necrosis in koi carp (Cyprinus carpio L)

Columnaris disease in koi carp

source: A. Decostere et al
Veterinary Record vol 150 no 22, June 1 2002
starts p694, 2 pages long

Columnaris disease is common among edible and ornamental fish found in cold and ornamental waters, and vets need to be able to recognise it and treat it in time, or it can cause heavy losses.

One case involved 25 Japanese koi carp, which were hit by an outbreak in May 2001. Their symptoms included hanging at the surface of the water, listlessness, and lack of appetite. They did not show discolourations or skin lesions. They then started gasping for air and lay side upwards, dying within 48 hours of first showing symptoms. Nine of the koi died during a four-day period. The temperature of the water was 20 deg c, while the pH, oxygen, ammonia and nitrate levels were normal.

The kois’ gills showed an excess of mucusy secretion, visible as yellowish-white areas through all the arches of the gill. Just a slight touch of the gill tissue led to haemorrhage. No parasites were found in the gills or skin, nor were there internal lesions found in post mortems of two euthanased fish. Affected gill tissue was studied by histological examination. There were necrotic cells, and long, slender bacteria in numerous clusters. The gill architecture had totally disappeared in some of the koi. Incubation using Shieh plates revealed F Columnare.

Treatment comprised oxytetracyline added at a dosage of 2.0g per 100 litres during three days, repeating the treatment four days later. An additional two koi died during the first day, but the remaining fish recovered, with an improvement in appetite and activity levels.

This disease has been linked to poor environmental conditions and stress, but this did not appear to be the case with these koi, and it may simply have been an especially virulent strain. There have been comments on the different virulence of strains of F columnare.

It is important to diagnose this disease early on, especially if a virulent strain is involved, since fish that are badly affected usually have to be euthanased, while earlu treatment can save the other fish. F columnare needs special media to grow, and blood agar cannot be used. Vets can spot the typical gill lesions, and can see the filamentous, long, slender bacteria, through microscopial examination of gills. Vets can start treatment before getting confirmation of the disease. Oxolinic acid, nifurprinol, and oxytetracycline have all been successfully used to treat this disease.


The eyes have it

Eye whites give off signals about health and social status of salmon

source: New Scientist September 22 2001 p25

The eye whites of salmon give off signals about the health and social status of the fish, according to Glasgow University’s Hayley Suter and team from the unit for fish biology. The sclera, or white of salomn’s eyes, is a light cream colour in dominant fish, becoming darker when the fish are ill. Dark sclera are found in fish of low status, and their eye whites become lighter if they are victorious in a battle, or eat a meal. A meal of a few worms can lighten the colour of a low-status fish’s eye white.


The tough get glowing

Genetically engineered zebra fish may be used to detect pollutants

source: Kristin Ohlson
New Scientist January 12 2002
starts p37, 2 pages long

Zebra fish have been genetically engineered to glow when pollutant levels are high. The fish were developed by University of Cincinnati’s Daniel Nebert, an environmental geneticist, and Michael Carvan, specialist in aquatic toxicology from the Great Lakes Water Institute of the University of Wisconsin-Milwaukee. The research has involved using both a gene that responds to dioxins and PCBs, and one that is involved in the production of luminescent chemicals used by fireflies. Fish tend to accumulate toxins in their bodies, and react quickly to rises in pollutant levels, though a luminometer has to be used to measure the glow, since humans cannot see it unaided. The fish provide a more sensitive way to detect pollution levels than most testing systems, except those that are extremely expensive.

There are important applications for this work, such as detecting pollutants in water supplying Clermont County from Lake Harsha, Ohio. This is a concern due to the location of a dump of hazardous waste only 8 km from the lake. A pilot study has already tested fish at a monitoring station for water quality for Clermont County, and eight out of the ten fish survived, though zebra fish are semi-tropical. The researchers have been unable to find enough funding to progress to building up stable zebra fish lines, despite the importance of their research.


Enemy within

Coral reefs may have been hit by a virus

source: James Randerson
New Scientist October 13 2001 p18

A virus may have affected corals, causing them to be more vulnerable to warmer seas temperatures, according to researchers from Plymouth’s Marine Biological Association. They argue that this could explain why not all corals are affected by warmer sea temperatures. The virus may be found in symbiotic algae that provide energy for corals, through photosynthesis. A sea anemone, Anemonia viridis, also has symbiotic algae. They heated water in which this anenome lives, and a virus in these algae multiplied rapidly. It is not certain whether corals are affected in this way, but they are closely related to anemones.