J. B. Jones

Environmental impact of trawling on the seabed: A review

Abstract Fishers have been complaining about the effects of bottom trawl gear on the marine environment since at least the 14th century. Trawl gear affects the environment in both direct and indirect ways. Direct effects include scraping and ploughing of the substrate, sediment resuspension, destruction of benthos, and dumping of processing waste. Indirect effects include post‐fishing mortality and long‐term trawl‐induced changes to the benthos. There are few conclusive studies linking trawling to observed environmental changes since it is difficult to isolate the cause. However, permanent faunal changes brought about by trawling have been recorded. Research has established that the degree of environmental perturbation from bottom trawling activities is related to the weight of the gear on the seabed, the towing speed, the nature of the bottom sediments, and the strength of the tides and currents. The greater the frequency of gear impact on an area, the greater the likelihood of permanent change. In deepe...

Treatments for ectoparasites and diseases in captive Western Australian dhufish.

The Western Australian dhufish (Glaucosoma hebraicum), an open-water marine finfish, has been identified as a potential species for aquaculture and a 4 y research project has concentrated on broodstock collection and maintenance, spawning and larval rearing. This paper describes treatments which were developed for the ectoparasites and diseases of broodstock fish. These included bacterial and fungal infections, Cryptocaryon irritans, Haliotremasp., an unidentified axinid monogenean, the isopod Aega cyclops and copepod Caligus sp. Treatments based on betadine, formalin, freshwater, malachite green, oxytetracycline (terramycin), 2-phenoxyethanol, potassium permanganate and trichlorphon (neguvon) were all tried. The most effective treatments against parasites were a freshwater bath or a combined freshwater bath and anaesthesia with 2-phenoxyethanol. Monogeneans on the gills were difficult to control and exophthalmia was an unresolved problem.

Movements of albacore tuna (Thunnus alalunga) in the South Pacific: Evidence from parasites

Parasites were collected from over 400 albacore (Thunnus alalunga) caught by surface trolling and longlining in the south-west Pacific between 1985 and 1988. Parasites found included 1 apicomplexan, 3 nematode species, 4 cestode species, 1 acanthocephalan, 12 digenean species and 3 copepod species. Twelve of these parasite species which could be accurately recognised and counted were used in the subsequent analyses. Parasite data from albacore caught around New Zealand show a decrease in prevalence of three didymozoid parasites with increasing fish length up to a fork length of 70 to 79 cm. The subsequent increase in prevalence of these didymozoids in large longline-caught fish is consistent with fish returning from spawning in tropical waters where re-infection is presumed to occur. Albacore collected at widely separate locations in the south-west Pacific have differences in parasite prevalence, supporting an hypothesis that juvenile albacore move south to New Zealand from the tropics and do not return until the onset of sexual maturity. Albacore appear to move along the subtropical convergence zone, as indicated by a decline in prevalence and abundance ofAnisakis simplex andHepatoxylon trichiuri from New Zealand to the central South Pacific. This is supported by tagging and seasonal movements of the fishery.

Australasian pilchard mortalities

A large-scale epizootic occurred in the Australasian pilchard Sardinops sagax between March and September 1995. The deaths occurred along 5000km of the Australian coastline and 500km of the New Zealand coastline. Affected fish died within a few minutes of clinical signs of respiratory distress and death was associated with hypoxaemia and hypercapnia. Significant lesions were confined to the gills and comprised acute to subacute inflammation followed by epithelial hypertrophy and hyperplasia. The lesions were initially focal but progressed to become generalized over about 4days. Only a herpesvirus was consistently present in gills of affected fish and absent from unaffected pilchards. There was no correlation with oceanographic conditions or the presence of plankton. The rate of spread of the mortality front (approximately 30km/day) in relation to the migration rate of pilchards and prevailing currents suggested that a vector might be involved. The disease may be the result of a virus introduced into Australian waters, or of a newly emerged virus.

Treatments to control Haliotrema abaddon in the West Australian dhufish, Glaucosoma hebraicum

Haliotrema abaddon is a significant monogenean parasite of the gills of maricultured Western Australian dhufish, Glaucosoma hebraicum, and can cause severe gill pathology. A series of trials was undertaken using infested fish in 120-l glass aquaria to assess the safety and efficacy of some potential “in water” treatments, including trichlorphon, praziquantel, formalin, toltrazuril and a freshwater bath. Treatment efficacy was established by assessment of the number of parasites found in tank sediment immediately following treatment and by examination of gills for parasites using a gill biopsy technique. Praziquantel bathes, 2 mg l−1 of 30-h duration, were the most safe and effective treatment. Freshwater bathes of below 2‰ salinity for 90 min were effective but highly stressful for the fish. Trichlorphon 0.5 mg l−1 for 30 h was safe and relatively effective. Formalin, 25 ppm, and toltrazuril, 12.5 mg l−1, were safe but resulted in the removal of insufficient parasites to recommend it as a treatment for dhufish infested with H. abaddon.

Growth of two species of freshwater crayfish (Paranephrops spp.) in New Zealand

Populations of Paranephrops planifrons and P. zealandicus were reared in aquaria and their growth rates monitored. When reared in unheated aquaria (10–21°c) P. planifrons grew to 20 mm orbit‐carapace length in 12–18 months and P. zealandicus reached the same size in 9–10 months. This is faster, for both species, than in feral populations. When reared in an aquarium at 18–21°C however, P. planifrons could be grown to 35 mm orbit‐carapace length in 18 months. Mortality in both species was very high (60–93%).

The molecular characterization of an Eimeria and Cryptosporidium detected in Asian seabass (Lates calcarifer) cultured in Vietnam

An intestinal Eimeria was previously reported as a significant pathogen of Asian seabass (Lates calcarifer) in nurseries in Vietnam. In the present study, both Eimeria and Cryptosporidium were detected by sequence analyses of fragments of the 18S rRNA gene amplified from these Vietnamese L. calcarifer tissues. Based on these analyses, the Eimeria from the Vietnamese L. calcarifer formed clades with the Eimeria detected in L. calcarifer tissues from Australia, but clustered separately from other known Eimeria and Goussia species. The Cryptosporidium detected in L. calcarifer from Vietnam clustered closest with C. parvum and C. hominis. In situ hybridization using DIG-labeled DNA probes generated from 18S PCR products on the Vietnamese L. calcarifer wax block tissues showed that this method could not be used to distinguish between Eimeria and Cryptosporidium, due to the conserved nature of the 18S locus. A previously published study on the morphology of parasite developmental stages and oocysts in the Vietnamese L. calcarifer tissues showed only an intestinal Eimeria infection. The Cryptosporidium could be present at very low levels undetectable by microscopy in intestines, or being ubiquitous, was a possible contaminant from feed or water. While molecular analysis is a very useful tool in the study of disease and identification of aetiological agents, this study reiterates the importance of demonstrating organisms in situ in tissues.

DISEASES OF PEARL OYSTERS AND OTHER MOLLUSCS: A WESTERN AUSTRALIAN PERSPECTIVE

Abstract Mollusc culture, particularly the cultivation of pearl oysters, is an important component of the aquaculture industry in Western Australia. As a result, there has been a long-term investment in surveys of commercial mollusc species for potential diseases of concern. A number of pathogens, particularly haplosporidans, identified within wild-stock shellfish have the potential to adversely affect mollusc populations. Others pose risks for translocations associated with aquaculture. The microsporidan Steinhausia mytilovum (Field), found in ova of the blue mussel Mytilus galloprovincialis (Lamarck), poses intriguing questions about the origin and dispersal of its host.

Diseases of yabbies (Cherax albidus) in Western Australia.

Routine disease testing of yabbies (Cherax albidus) in Western Australia for over 10 years revealed only few diseases of significance to freshwater crayfish aquaculture. The most serious of these are the recent discoveries of an introduced microsporidian Thelohania sp. and a previously undescribed virus that has been associated with mortalities in yabby dams but has a widespread distribution with low prevalence (<5%). Other parasites and ectocommensals have been recorded from C. albidus in Western Australia including temnocephalans, cilliates, Psorospermium sp. and the nematode Gammarinema sp. However, these appear to have little effect upon the host other than lowering their market value. Testing for crayfish plague (Aphanomyces astaci) since 1989 has shown that this disease is not present in Western Australia. Although many farmers feed lupin seeds (Lupinus angustifolius) to crayfish in Western Australia, this practice can result in mortalities due to enterotoxaemia.

An intestinal Eimeria infection in juvenile Asian seabass (Lates calcarifer) cultured in Vietnam – A first report

This is the first report of an intestinal Eimeria infection in Asian seabass (Lates calcarifer) at the histopathological and ultrastructural levels. The Eimeria infection was often associated with severe pathology and significant mortality in the absence of other pathogens. This showed that it is an important disease of juvenile L. calcarifer in small scale nurseries in Vietnam. Heavy infection and high prevalence levels of the Eimeria infection are suspected to be linked to the low daily water exchange rates practised in these nurseries. Although systemic iridovirus infection was concurrently observed in some of the fish examined, it was not as consistently present in diseased fish as the Eimeria infection.