Over the past 80 years, tilapia have been translocated globally for aquaculture; active production is recorded in >124 countries. Of 7 million tonnes of tilapia produced in aquaculture, 79% is from 79 countries outside the natural range of tilapia. Capture fisheries account for a further 723,627 tonnes of tilapia, and >47% of this is landed from established invasive populations outside Africa. Tilapias host a rich fauna of par...

The influence of parasitism on first‐year growth and recruitment success of two cyprinid species in the Yorkshire Ouse catchment, England, was investigated using a 14‐year dataset. This study demonstrated a significant role of parasitism in growth and recruitment success of roach, Rutilus rutilus (L.), and European chub, Squalius cephalus (L.) populations. Muscle infections by Bucephalus polymorphus Baer (Digenea), Myxobolus p...

There is a bewildering array of fish parasites and probably all fish species harbour one or more species. Under normal conditions hosts often show little or no signs of infection, either clinically or at the organ and tissue level. All tissues can be infected, including the blood. Coelozoic species generally do not elicit significant host responses. Any developmental stages, however, where these migrate through the host tissue...

The prevalence of renal myxosporidiosis in wild brown trout, Salmo trutta , in seven river catchments in South‐West England was investigated. Three hundred and twenty‐seven fish were sampled from 16 sites, of which 54 (16.5%) were found, by histological examination of the kidney, to be infected with Tetracapsuloides bryosalmonae , the causative agent of proliferative kidney disease. No T. bryosalmonae infected fish were found...

Since its first introduction to English waters in the mid 1980s, sunbleak Leucaspius delineatus has spread widely and it is shown in the present study that this non‐native cyprinid is a new host for Neoergasilus japonicus . This copepod parasite from South East Asia has a limited host range and distribution in the U.K. Rapid dispersal of sunbleak in the U.K. raises concerns for further dispersal of this introduced parasite.

Approximately 5000 young of the year (0+) cyprinids comprising roach, chub, dace, minnow, bleak, bream, barbel and gudgeon were examined histologically for the presence of myxozoan infections. Thirteen myxozoans were identified to species, the majority being Myxobolus spp. In addition, two species of Myxidium and of Sphaerospora were recorded. All organs were examined, with the majority of infections being found in the gills,...

Bullheads, Cottus gobio , with macroscopic external cysts on the skin and fins measuring up to 3 mm in diameter were detected in the River Allen and its tributaries in southern England between 1992 and 1998. The prevalence of these cysts was up to 50% at some sites. Examination of cyst contents revealed the presence of numerous spores, typical of the genus Dermocystidium , measuring 8 μ m in diameter. The parasite developed wi...

The initial site of infection in the fish host for Tetracapsula bryosalmonae , causative agent of proliferative kidney disease (PKD) is poorly understood. Following the recent recognition that freshwater bryozoans harbour the infective stages to salmonid fish, experimental transmission studies were undertaken to investigate (1) the route of entry of the parasite into the fish host and (2) the minimum exposure time required to...

The results from a survey for proliferative kidney disease (PKD) and renal myxosporidiosis in wild salmonids from rivers in England and Wales are presented. One hundred and eighty‐five salmon, Salmo salar , 235 brown trout, Salmo trutta , 16 charr, Salvelinus alpinus, and five grayling, Thymallus thymallus, were obtained from 23 locations on 16 rivers between July and October 1997. They were examined for the presence of clinic...