Table 2.

Symptomatology of important diseases caused by virus, bacteria, and parasites.

Disease	Pathogen	Host	Clinical Signs/Pathology	References
Virus
Epizootic haematopoietic necrosis (EHN)	Epizootic haematopoietic necrosis virus	Redfin perch (Perca fluviatilis), Rainbow trout (Oncorhynchus mykiss)	Erratic swimming, darkened skin, skin ulcers, exophthalmia, swollen spleen and kidney, petechial haemorrhages on fins, ascites, abdominal distension	[131]
Infectious haematopoietic necrosis (IHN)	Infectious haematopoietic necrosis virus	Salmonids	Lethargy, darkened skin, exophthalmia, eye haemorrhage, pale gills, swollen abdomen, opaque faecal casts, petechial haemorrhage on fins, visceral pallor	[132,133]
Infectious Pancreatic Necrosis (IPN)	Infectious pancreatic necrosis virus	Salmonids	Irregular swimming, loss of appetite, darkening of the skin, distended abdomen, exophthalmia, pale gills petechial haemorrhages, visceral ascites, intestine with catarrhal exudate and pale liver	[134,135,136]
Infectious salmon Anaemia (ISA)	Infectious Salmon Anaemia virus	Atlantic salmon (Salmo salar)	Lethargy, anaemia, exophthalmia, pale gills and internal organs, ascites, oedemas, petechiae in visceral fat, liver and spleen congestion	[137,138]
Lymphocystis disease	Lymphocystis disease virus	Broadly infectious	Nodular lesions on the skin, fins and internally	[137]
Pancreatic disease (PD)	Salmonid alphaviruses (SAV)	Rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar)	Lethargy, hang in the corners of the cage or rest in the bottom, loss of appetite, yellow faecal casts, ascites, petechial haemorrhages in pyloric caecal fat, lesions in pancreas and skeletal and cardiac muscle	[139,140]
Viral haemorrhagic septicaemia (VHS)	Viral haemorrhagic septicaemia virus	Broadly infectious	Aberrant swimming (spiral, leaping, flashing), exophthalmia, darkened skin, anaemia, pale gills and liver, internal haemorrhages, ascites leading to a swollen abdomen, swollen and hyperaemic kidney	[137,141]
Viral nervous necrosis (VNN)	Betanodaviruses	Broadly infectious	Lethargy, abnormal swimming; anorexia, skin darkening, abdominal distension, hyperinflation of the swim bladder	[142,143]
Bacteria
Vibriosis	Vibrio anguillarum	Broadly infectious	Lethargy, cease feeding, darkened skin, exophthalmia and corneal opacity, pale gills, petechiae at fin bases and skin, ulcers, generalized septicaemia	[127,144,145]
Pasteurellosis	Photobacterium damselae subsp. piscicida	White perch (Morone americanus) yellowtail (Seriola quinqueradiata) gilthead seabream (Sparus aurata)	Darkened skin, swollen spleen, white-spotted lesions in spleen and kidney, bacterial accumulations on the tissues of internal organs	[146,147]
Furunculosis	Aeromonas salmonicida subsp. salmonicida	Broadly infectious	Lethargy, cease feeding, darkened skin, exophthalmia, haemorrhages at the base of the fins, enlarged spleen, lesions on the skin (furuncles), ulcers, pale liver, general septicaemia	[148,149]
Tenacibaculosis	Tenacibaculum maritimum	Broadly infectious	Flashing swimming behaviour, anorexic, erosion on the skin, fins (tail rot), head and gills, petechial haemorrhage on the abdominal peritoneum, ulcers	[150]
Bacterial gill disease (BGD)	Flavobacterium branchiophilum	Coldwater fish (mainly salmonids)	Loss of appetite, gill infestation, increased opercular movements, gasping at the water surface, respiratory distress	[151]
Rainbow Trout Fry Syndrom (RFTS)	Flavobacterium psychrophilum	Salmonids	Lethargy, anorexia, distended abdomen, darkened skin in caudal peduncle area, skin ulceration, swollen spleen, pale organs	[152]
Red spot disease (Winter disease)	Pseudomonas anguilliseptica	Eels, salmonids, gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), European cod (Gadus morhua)	Erratic swimming, petechial haemorrhages in the skin and liver, distended abdomen, ascitic fluid in the peritoneal cavity, pale liver, haemorrhaged kidney, intestine with yellowish exudate	[144,153]
Disease	Pathogen	Host	Clinical Signs/Pathology	References
Lactococcosis	Lactococcus garvieae	Broadly infectious	Lethargy, anorexia, exophthalmia, distended abdomen, ascitic fluid in the peritoneal cavity, congestion and haemorrhages of liver, intestine, spleen and kidney, haemorrhagic septicaemia	[154]
Parasites
Amoebic gill disease (AGD)	Neoparamoeba perurans	Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss)	Lethargy, respiratory distress, increased opercular movements, whitish patches on gills and excessive mucus	[155,156]
White spot disease/Ichthyophthiriasis	Ichthyophthirius multifiliis	Freshwater fish	Hyperactive (initially), lethargic; pale gills, darkened skin, white spots in the skin, increase of mucus production, skin ulcers, frayed fins, pale liver, enlarged spleen and kidney	[128,157,158]
White spot disease/Cryptocaryoniasis	Cryptocaryon irritans	Saltwater fish	Hyperactive (initially), lethargic, numerous small whitish spots on the skin surface, petechial haemorrhages on the skin, excessive mucus production, skin ulcers, corneal clouding and blindness	[128,159]
Amyloodiniosis	Amyloodinium ocellatum	Broadly infectious	Cease feeding, scratch against the bottom, infested gills and skin, excessive mucus production, epithelial erosion on attachment sites	[160,161,162]
Trichodinosis	Trichodina sp.	Broadly infectious	Lethargy, cease feeding, infested gills, skin and fins, Greyish colour due to excessive mucus production, skin lesions in attachment sites, frayed fins	[163,164]
Gyrodactilosis	Gyrodactylus salaris	Salmonids	Infest mainly fins and skin, lethargy, anorexia, emaciated fins, darkened skin, epithelium lesions	[165,166]
Sea lice	Lepeophtheirus salmonis	Salmonids	Skin lesions, especially on the head, haemorrhages, scale loss, oedema, hyperplasia and cellular inflammations	[167]