This paper describes the pathology of fin erosion in a feral population of goldfish Carassius auratus ( L . ) exposed to bleached kraft mill effluent in the Waikato River, New Zealand. Acute fin erosion is initially characterised by hyperplasia of the epidermis, loss of the cuticle and of the epidermal microridges, and the rounding and eventual sloughing of the outermost squamous cells. It typically involves a n increase in the number of pigment cells, particularly in the marginal zones of the affected fins, thus accounting for the characteristic black edge of eroded fins. A lymphocytic reaction of variable extent and epidermal oedema are also evident in the acute phase of fin erosion as are increased numbers of mucous cells and decreased numbers of alarm cells in the epithelium. The stratum germinativum and basement membrane of an acutely eroded fin are typically thickened. As fin erosion progresses, increased sloughing of the epidermal cells thins the epidermis. Cells in the stratum germinativum become enlarged and vacuolar and may lift from the basement membrane. Dermal oedema and fibrosis develop early in the progression of the disease with the later stages involving loss of the dermis and erosion of the lepidotrichia. Healed erosion is characterised by dermal fibrosis and the presence of a node of thickened lepidotrichia that is largely unsegmented. New fin rays are formed distally, but they are not continuous initially with the old fin ray stumps. Longitudinally oriented lepidotrichia-forming cells are apparent at the distal tip of the node and in foci distal to the nodal area. Melanophores and basophilic fibroblasts are also abundant and surround each area of fin ray deposition during the healing process. Only in the final stages of healing do the fin rays became continuous with the old fin ray stumps at the node, and the newly formed rays acquire segmentation. Fin erosion as described here is a unique and definitive pathological condition which may have potential as a bioindicator for a variety of pollutants including pulp mill effluents.

The metazoan parasites of the snapper Pagrus auratus were surveyed from specimens collected in north-eastern New Zealand. Nine species of ectoparasites were recorded. These included five monogeneans (Benedenia sekii on the body surface, Anoplodiscus cirruspiralis on the caudal fin, and Lamellodiscus pagrosomi, Choricotyle australiensis, and Bivagina pagrosomi attached to the gills) and four copepods (Unicolax chrysophryenus within the nasal sinuses, Lepeophtheirus sekii and two species of Caligus free on the body surface). A further two copepods, Hatschekia pagrosomi and Clavellopsis sargi, previously described from snapper but not collected during this study, bring the total number of ectoparasites known to parasitise snapper in New Zealand to 11. The two Caligus species recorded from the body surface of Pagrus auratus in this study are described for the first time. They are significantly different from those described previously by Roubal et al. and Byrnes. The faunal composition of the metazoan ectoparasites off. auratus from New Zealand is compared with that described from snapper in Australia and Japan.

The metazoan parasites of the snapper, Pagrus auratus, collected in the Hauraki Gulf of New Zealand were surveyed and their distribution mapped and examined in relation to the age of the host. Nine species of ectoparasites and seven species of endoparasites were recorded and all were found to exhibit some degree of site-specificity. The gill monogeneans Lamellodiscus pagrosomi and Bivagina pagrosomi were found in well-defined microhabitats on the gills. L. pagrosomi was abundant on the middle section of the second gill arch and was found in greater numbers on the distal zone of the gill filaments of the external hemibranch. In contrast, B. pagrosomi was particularly abundant on the first gill arch and on the basal zone of gill filaments of the external hemibranch. A third gill monogenean, Choricotyle australiensis, was found attached to the gill filaments in snapper of 3 years and older but was largely restricted to the buccal cavity in younger host fish. This suggests that site-specificity may not be a static attribute but may alter along with other parameters of the host fish such as age and size. The gastro-intestinal parasites were also found to exhibit habitat partitioning and segregation into specific niches with a highly site-specific digenean, Diphtherostomum sp., occurring almost exclusively in the lumen of the rectum.

The prevalence and abundance of nine species of ectoparasites and seven species of endoparasites found on the snapper, Pagrus auratus, collected from the Hauraki Gulf, New Zealand, is reported. The metazoan fauna of Pagrus auratus in this study was dominated by a single highly prevalent and abundant species, Diphtherostomum sp., which accounted for 84% of all the parasites collected during this study and occurred in all snapper older than 2 years. Several other moderately abundant species were highly prevalent, occurring in 50-60% of the snapper sampled. These included Lamellodiscus pagrosomi, Bivagina pagrosomi, Cucullanus sp., and Unicolax chrysophryenus. The remainder of the parasite fauna comprised rare species of limited prevalence and low abundance, accounting for 7.7% of the individuals collected. These included Choricotyle australiensis, phyllobothriid and dasyrhynchid plerocercoids, Proctoeces sp., Philometra lateolabracis, and Anisakis sp. Correspondence analysis indicated that different age classes of the host snapper had distinctive parasitic faunas, with 0+ snapper characterised by low abundance and prevalence of all species except C. australiensis and the phyllobothriid plerocercoid. A progressive increase in many of the species of parasites constituted the major faunistic differences between 1+, 2+, and 3+ snapper. The implications for fisheries and aquaculture of the composition of the metazoan parasitic fauna of P. auratus are discussed.

The metazoan parasites of the snapper Pagrus auratus were surveyed from specimens collected in north-eastern New Zealand. Seven species of endoparasites were found, five in the digestive tract. These included two digeneans (Proctoeces sp. and Diphtherostomum sp.), two cestode plerocercoid larvae (belonging to the Families Dasyrhynchidae and Phyllobothriidae), and a nematode (Cucullanus sp.). Two other nematodes were also found, one in the gonad (Philometra lateolabracis) and the other (Anisakis sp.) encapsulated in the mesenteries adjacent to the rectum and on the peritoneal lining. Five of the seven endoparasites collected in this study (Proctoeces sp., Diphtherostomum sp., Cucullanus sp., and the two cestode plerocercoids) have not been previously recorded from P. auratus in New Zealand. A further three endoparasites have been described previously from snapper but were not collected during this study. The faunal composition of the metazoan endoparasites of P. auratus from New Zealand is compared with that described from snapper in Australia and Japan.