J. F. Turnbull

Attack site and resultant damage during aggressive encounters in Atlantic salmon (Salmo salar L.) parr

Fin rot is a term used to describe a range of changes in fins, from splitting and erosion to nodular thickening. It is common among farmed Atlantic salmon (Salmo salar) parr and is of considerable economic and welfare importance. Fin rot is known to commence when fins become damaged, for example, following attacks by conspecifics; however, not all fins are equally affected, the dorsal fin being much more frequently damaged. This study examined the hypothesis that fin rot is more prevalent in the dorsal fin because it is more frequently attacked during aggressive encounters with conspecifics. Behavioural observations showed that the dorsal and caudal fin areas are much more frequently attacked than other areas of the body and significantly more attacks directed at the dorsal fin area resulted in physical contact than attacks directed at other parts of the body. Fin damage, scored as the total amount of fin splitting was highest in the dorsal and pectoral fins despite the pectoral fins being attacked less frequently than the dorsal or caudal fins. This suggests that pectoral fins may have sustained damage through contact with the tank as well as through attacks. We conclude that at least one reason for the observed prevalence of fin rot in the dorsal fin of Atlantic salmon in aquaculture systems is that it is a preferred site of attack by conspecifics and because attacks are more likely to end in physical contact than attacks on other areas of the body and, thus, they sustain more damage.

Effect of water treatment and aeration on the percentage hatch of demersal, adhesive eggs of the bullseye puffer (Sphoeroides annulatus)

The bullseye puffer (Sphoeroides annulatus) is a species with potential for aquaculture. However, preliminary studies on the biology and reproduction of the species in captivity have failed to produce consistent success at hatching. In this study, the effect of aeration and water treatment (filtration and ultraviolet (UV) sterilisation) on percentage hatch was assessed in a replicated experiment repeated on two occasions. Four treatments were used, filtered water (5 μm) treated with UV, in an aerated system (AT) and a static system (ST); water that had been coarse-filtered (20 μm) and not exposed to UV kept in aerated system (ANT) and a static system (SNT). The percentage hatch was ranked 87.5±5.0>80.6±9.4>77.2±12.8>62.8±10.4 (mean of all replicates from both experiments±S.D.) for the respective treatments AT>ST>ANT>SNT. However, percentage hatch for AT was only significantly (P<0.05) higher than ANT and SNT, while hatch for ST was only significantly higher (P<0.05) than SNT. A GLM analysis showed the use of treated water (filtered and UV treated) in the incubators and aeration had a significant positive effect on percentage hatch. These effects were additive with no significant positive or negative interaction. There was no significant differences in bacterial counts among treatments (AT, ANT, ST, SNT), but significant differences (P<0.05) were observed among days. There was no significant interaction between days and treatments to affect bacterial counts. There was no correlation between bacterial counts and percentage hatch. The water treatments significantly improved percentage hatch, but did not affect bacterial counts. This paper reports an incubation system that consistently resulted in more than 80% successful hatching for bullseye puffer eggs. These results should help to improve the hatching success of this species and possibly others with demersal adhesive eggs.

Histopathology and Ultrastructure of Segmented Filamentous Bacteria–Associated Rainbow Trout Gastroenteritis

Rainbow trout gastroenteritis (RTGE) is an emerging syndrome linked to the presence of large numbers of the segmented filamentous bacterium “Candidatus arthromitus” within the intestine. The present study examined the histopathological changes of the digestive tract of 152 trout with gross lesions typical of RTGE. Histopathology showed that 129 of 152 fish (85%) affected with RTGE had segmented filamentous bacteria in the distal intestine and/or pyloric caeca. The presence and number of segmented filamentous bacteria were always significantly higher (P < .001) in pyloric caeca, thereby suggesting the preferred site for these bacteria. Histopathological changes included enterocyte detachment and congestion of the lamina propria and adventitial layers. Samples from 6 RTGE-affected trout were examined using scanning and transmission electron microscopy, revealing a close interaction of segmented filamentous bacteria with the mucosa of distal intestine and pyloric caeca, with the presence of bacterial attachment sites, and with associated morphological changes of the apical membrane of enterocytes. Despite these interactions, segmented filamentous bacteria were not always adjacent to the areas with pathological changes, suggesting that if these organisms play a role in the pathogenesis of RTGE, extracellular products may be involved. Ultrastructural changes included loss of microvillar structure, membrane blebbing, hydropic mitochondrial damage, and basal hydropic degeneration of enterocytes, which frequently resulted in disruption of tight junctions and enterocyte detachment. The resulting exposure of large areas of lamina propria probably resulted in the compromise of the host osmotic balance and the facilitation of the entry of secondary pathogens.

Clinical white spot disease status in Penaeus monodon during the middle of the culture period - its epidemiological significance.

1 Fish Pathology and Biotechnology Laboratory, Department of Aquaculture, College of Fisheries, Mangalore, Karnataka, India 2 Network of Aquaculture Centers in Asia Pacific (NACA), Kasetsart University Campus, Bangkok, Thailand 3 Aquaculture and Aquatic Animal Health Specialist, Hanoi, Vietnam 4 Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, United Kingdom 5 Research Institute for Aquaculture No. 2, 116 Nguyen Dinh Chieu Street, Ho Chi Minh City, Vietnam 6 Department of Veterinary Clinical Science and Animal Husbandry, The University of Liverpool, Leahurst, Neston CH64 7TE, United Kingdom 7 International Finance Corporation, World Bank Group, Banda Aceh, Indonesia

A study of gross, histological and blood biochemical changes in rainbow trout, Oncorhynchus mykiss (Walbaum), with rainbow trout gastroenteritis (RTGE)

The mechanisms behind the pathogenesis of rainbow trout gastroenteritis (RTGE) are still unknown. This study examined the macroscopic and microscopic changes in trout with RTGE (RTGE+), as well as the blood chemistry. A total of 464 rainbow trout were sampled from 11 sites in the UK, comprising 152 RTGE+ fish and 330 random, apparently healthy fish. A case definition for RTGE was assessed by the analysis of its agreement with three laboratory tests: histopathology, packed cell volume and kidney bacteriology. Cluster analysis indicated the presence of three distinct presentations within the population of RTGE+ fish. Cluster A included gross signs associated with moribund RTGE+ fish, and clusters B and C identified gross signs consistent with concurrent diseases, notably furunculosis, enteric redmouth and proliferative kidney disease. The information gained was used to select RTGE+ fish without concurrent disease for the analysis of RTGE pathogenesis with blood biochemistry. This analysis revealed a severe osmotic imbalance and a reduced albumin/globulin ratio as indicatives of selective loss of albumin. These findings are compatible with a protein losing enteropathy.