PARASITES AS POTENTIAL STOCK MARKERS FOR TUNA IN INDONESIAN WATERS

Tuna fish are highly migratory species. Clarifying their stock structures and migration patterns is important for tuna fisheries management. The purpose of this research was to examine the parasites of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) to determine which parasites may be potential stock markers for assessment of tuna migration patterns. Bigeye tuna and yellowfin tuna were collected (measured between 28-48 cm fork length) from 9 sites across Indonesia and from 2 ‘outlier sites’ (The Maldives and Solomon Islands). Organs including gills (filaments and branchial arches), stomach wall, liver, pyloric caeca, and intestines were examined. Seven types of didymozoids were distinguished including 3 Didymosulcus spp., 4 Kollikeria spp. and one acanthocephalan (Bolbosoma sp.). The results suggest these fish parasites are potentially useful markers for assessment of tuna migration pattern, contributing information needed for fisheries management in Indonesia

A review of methods for estimating mortality due to parasites in wild fish populations

Six methods are described for detecting mortality due to parasitic infections in natural fish populations. They are: (a) through autopsies; (b) by determining the frequency of infections known to be eventually lethal; (c) by observing a decrease in the prevalence of a long-lived parasite (or permanent scar from a parasite) with host age; (d) by observing a decrease in the variance/mean ratio for the parasites with host age; (e) by comparing the observed frequency of a combination of two independent events with the calculated probability of their occurrence; and finally (f) by comparing the observed frequency distribution of the parasite, with a projected frequency based on data from lightly infected fish. In this technique, negative binomials are fitted to the data and truncated at various points. Some advantages and disadvantages of the different methods are given, together with examples. The methods do not necessarily provide definitive answers, but they are indicative of whether or not significant parasite-related mortality may be occurring, and in some cases provide an estimate of its probable magnitude in terms of the total host mortality rate

Reappraisal of the use of parasites for fish stock identification

Analysis of the geographical distributions of parasites is an excellent source of information about the movement of host fish. Occasionally such analysis can also allow us to discriminate between fish populations, though unequivocal discrimination usually requires methods with a genetic basis. In assessing fish movement, parasites have two advantages over conventional tags: They can more readily detect mass migration and, because the fish only have to be caught once, the data are usually cheaper to obtain. The most important criterion in selecting a parasite to be used as a tag is its longevity in the fish; short-lived parasites give information on short-term movements of the fish, long-lived parasites on more extensive migrations

Growth, mortality, parasitism, and potential yields of two Priacanthus species in the South China Sea

In the northern part of the South China Sea the ‘big‐eye’, Priacanthus tayenus, spawned once a year in June, had von Bertalanffy growth parameters of k = 0.8 and L∞= 30 cm, and a mean total annual instantaneous mortality of Z= 2.0, calculated from adjusted catch curves and a mean length equation. The natural mortality rate M= 1.4, fishing mortality rate F= 0.6, and the exploitation rate (E) was 0.27. The maximum potential yield, calculated using Marten's method, was 0.06 kg/recruit when F= 5.4. The fish were heavily parasitised by the protozoan Pleistophora priacanthicola. A second big‐eye, P. macracanthus, spawned twice a year in May‐June and September, had growth parameters of κ= 0.7 and L∞= 32, and population parameters of Z= 2.0, .F= 0.7, and E= 0.34. The maximum potential yield was 0.13 kg/recruit when F= 5.8. A marked reduction in fishing mortality occurred for both species between 1965 and 1966, coinciding with the onset of the Chinese Cultural Revolution. Our estimates of maximum potential yield correspond to fishing mortalities eight times estimated levels, though such heavy exploitation could risk recruitment failure. Copyrigh

Viral diseases of penaeid shrimp with particular reference to four viruses recently found in shrimp from Queensland

The culture of penaeid shrimp world-wide is primarily dependent on wild-caught broodstock which has an enormous potential to introduce new pathogens, particularly viruses, into culture systems. Of the 13 viruses described for cultured penaeid shrimp, seven have been described within the past 5 years; the most devastating viral epidemics on record for cultured penaeid shrimp have also occurred within the past 5 years. During examination of local wild and cultured shrimp, four new viruses were found. Bennettae baculovirus was discovered in the digestive gland of wild Metapenaeus bennettae. It closely resembles monodon baculovirus (MBV) but has a more slender virion, does not cross-react with a DNA probe for MBV and is not infectious to Penaeus monodon. Two morphologically indistinguishable viruses, one pathogenic (gill-associated virus, GAV) and the other benign (lymphoid organ virus, LOV), were found in cultured P. monodon. LOV and GAV closely resemble yellow head virus (YHV) of Thailand. A parvo-like virus was found recently in dying post-larvae of P. japonicus. As the intensity of shrimp culture world-wide increases, researchers can expect to discover more penaeid viruses. The need to close the life cycle of P. monodon and other cultured species and develop rapid diagnostic methods for viral infections has become imperative

Baculovirus of Metapenaeus bennettae from the Moreton Bay region of Australia

Adult Metapenaeus bennettae shrimp, trawled from Moreton Bay, Australia, were found infected with a baculovirus which resembled Monodon Baculovirus (MBV) in its ultrastructure and histological appearance. It differed in that infected material gave negative results with an in situ hybridization test using a DNA probe for MBV, and Penaeus monodon postlarvae, experimentally exposed to the virus, failed to become infected. This new baculovirus, designate MbSNPV or Bennettae Baculovirus (BBV), is the first virus reported from a Metapenaeus spp. taken from the wild

Parasites and symbionts of wild mud crabs Scylla serrata (Forskal) of potential significance in aquaculture

A total of 130 wild mud crabs, Scylla serrata, from Moreton Bay, Queensland, were examined to determine if there were parasites or symbionts that could cause problems in aquaculture. Of 10 parasites and symbionts found, four were potential pathogens. The blood protozoan, Haematodinium sp. is similar to parasites that have killed crabs else-where. The ciliates, Epistylis sp. and Acineta sp., and the barnacle, Octolasmis cor. were common on the gills and may increase stress through respiratory distress. Both of the ciliates showed seasonality, with Epistylis sp. abundant in summer and Acineta sp. abundant in winter. Haematodinium sp. was present at low prevalence throughout the year. The prevalence of Octolasmis cor was significantly higher in female crabs than in males. Mean intensity was positively correlated with crab size for O. cor and for the metacestode of Polypocephalus sp. The prevalence of Epistylis sp. and the barnacle, Chelonibia patula, varied with the moult stage of the crab

Udonella myliobati n. comb. (Platyhelminthes: Udonellidae) and its occurrence in Eastern Australia

A total of 2,571 of the copepod Caligus epidemicus Hewitt from the yellow-fin bream, Acanthopagrus australis Günther, was examined for udonellids. Calinella myliobati Guberlet, 1936 was found on 3.3% of male copepods and 10.1% of female copepods. A new combination, Udonella myliobati (Guberlet, 1936) is proposed and its description emended. It differs from the type species Udonella caligorum Johnston, 1835 (as described by Price [1938]) in having a short egg filament and a median genital aperture. Only 1 of 102 chalimus larvae was infected, by a single adult worm. Juvenile udonellids common on mature copepods, were not found on any of the chalimus larvae. The highest number of U. myliobati (Guberlet, 1936), including hatching and unhatched eggs on 1 copepod, was 159. Adult and juvenile worms were attached mainly along the margins of the carapace and to the genital complex, whereas the majority of the eggs were attached to the ventral surface of the genital complex. The transfer of an adult worm from a male copepod to a female copepod was observed while the copepods were copulating. The large number of udonellids on a small population of mostly female copepods from the Brisbane River suggested that this was an aging population of copepods compared to the copepods collected from a semi-enclosed pond

Variation in the development of two isolates of Cryptocaryon irritans

Two isolates of Cryptocaryon irritans obtained from Acanthopagrus australis from Moreton Bay (isolate C1) and Gymnocranius audleyi from Heron Island (isolate C2) were passaged on Lates calcarifer and Macquaria novemaculeata at 20 and 25 C under identical laboratory conditions. There were significant differences between isolates in the diameter of trophonts and tomonts, the incubation period of tomonts, and the length of theronts. Trophonts of C1 were significantly larger on L. calcarifer than on M. novemaculeata and showed marked size variation with temperature, whereas trophonts of C2 developed equally well on both species and showed little size variation with temperature. Tomonts of C1 were significantly larger than those of C2 when grown on L. calcarifer, whereas on M. novemaculeata tomonts from C1 were significantly smaller than C2 tomonts. The incubation period of tomonts from C1 was significantly shorter than that for tomonts of C2, and theronts of C1 were significantly larger than theronts of C2 under all host/temperature conditions. The differences in the development of these isolates are of biological and epidemiological importance. This indicates that distinct intraspecific variants of C. irritans occur along the coast of southeast Queensland

Description of and observations on Grillotia branchi n.sp., a larval trypanorhynch from the branchial arches of the Spanish mackerel Scomberomorus commersoni

A new species of trypanorhynch is described from blastocysts found within the gill arches of Scomberomorus commersoni caught off eastern Australia. It differs from other members of the genus in having 9 to 10 hooks per principle row, scattered intercalary hooks that merge with the band of small hooks, and a well-developed basal armature. Developing stages were found both within and outside branchial blood vessels. Thousands of fully developed blastocysts were within the gill arches. Around and between them was fibrous tissue, haemorrhage, and evidence of chronic inflammation. ac]1981021