You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Many owners consider fish to be the staple diet of cats - and they believe that it is beneficial to feed them an exclusively fish ration.

Fish is a good raw ingredient to incorporate into cat foods, but it has certain draw backs. Firstly it does not contain all the nutrients that a cat requires and, like meat, it is deficient in calcium with an inverse calcium:phosphorus ratio. Coley (or Saithe) a popular fish with cat owners in the UK and the fillet cut contains 15-20 mg calcium per 100g but over 200 mg phosphorus per 100g, a Ca:P ratio of 1:10. Cod and other white fish are similar.

If owners are feeding fish bones should be removed to avoid complications. Fish should be cooked to avoid the possibility of disease transmission. 

"Salmon poisoning" has been recorded in cats which contracted the disease caused by Neorickettsiae spp from eating raw salmon or trout. This disease occurs within 2 weeks of the ingestion of infected food and causes the following signs :

• Depression
• Fever
• Lymphadenopathy - swelling of the lymph nodes
• Oculonasal discharge
• Haematemesis - vomiting blood
• Diarrhoea
• Death - 90% in untreated cases.

Diagnosis is confirmed by finding trematode eggs in faeces samples, or rickettsiae in lymph node samples.

Clinical cases of thiamine deficiency are periodically seen by veterinarians due to cats being fed  fish - as commercially prepared canned food, or as raw fish. Thiamin (vitamin B1) is an essential dietary nutrient for cats. Processing can destroy thiamine in a food, and so reduce the initial concentrations present at canning, and some fish (including herring and carp) contain the thiaminase which will destroy thiamine.

Clinical signs of thiamine deficiency include :

• Anorexia
• Ataxia - 2-3 days later
• Vomiting
• Convulsions - short 
• Dilation of the pupils
• Ventroflexion of the neck (Chastek's paralysis)

Affected patients will die unless treatment is administered (100-250 mg thiamine IV or SC twice daily). In most cases a complete recovery can be expected in treated cases unless severe central nervous system has occurred. 

Confirmation of diagnosis is not readily available :

• Increased plasma pyruvate
• Increased plasma lactate
• Reduced erythrocyte trans-ketolase activity (a thiamine-dependant enzyme)

Some fish are particularly high in oil content, and pansteatitis or "yellow fat disease" is caused by the intake of too much fat in the absence of adequate antioxidant. Red-meat tuna has been reported to be particularly involved as a cause of this in cats. The cause of the disease is accumulation of peroxides - the end product of rancidification of fat - in the cats adipose tissue causing yellow-brown discolouration.

Clinical signs of pansteatitis include :

• Abdominal Pain
• Anorexia
• Fever
• Lethargy
• Hardening of subcutaneous and intra-abdominal fat depots
• Occasionally ascites (low in protein content;  compare with FIP - high in protein content)

The condition is treated with dietary management (a complete and balanced diet), Vitamin E supplementation (30mg alpha-tocopherol/day ) , and some authors recommend the use of corticosteroids.

Updated October 2013