Comparative histopathology of Longicollum (Acanthocephala: Pomphorhynchidae) infection in the alimentary tract and spleen of Acanthopagrus australis (Pisces: Sparidae).

The pomphorhynchid acanthocephalan Longicollum alemniscus infected the rectum of 16 and the intestine of five of 628 Acanthopagrus australis from Moreton Bay, Queensland. The neck and proboscis penetrated the entire gut wall and were surrounded by a layer of compact, rounded fibroblasts inside a layer of elongated fibroblasts and scattered connective tissue fibres. These layers extended across the entire gut wall and into the capsule that enclosed the proboscis outside of the gut. A similar parasite occurred extraintestinally in three fish; the proboscis of one penetrated into the spleen. The spleen was shrunken, with the proboscis and anterior part of the neck enclosed in a capsule of proliferated connective tissue and cellular elements similar to that in the response to infection of the gut wall.

Microhabitats, attachment of eggs and histopathology by the monogenean Allomurraytrema robustum on Acanthopagrus australis (Pisces: Sparidae).

Allomurraytrema robustum occurs normally in low numbers on the jaws, gill arch or upper palate; juveniles also occur on the lateral margins of the gill filaments. At high levels of infection the parasite occurs in large groups (> 30 worms) on the jaws and gill arches, and extends onto the lateral margins of the gill filaments. Large numbers of eggs become entangled among these groups of parasites. Ciliated oncomiracidia emerge from the eggs. The parasite attaches to the surface of epithelia by small hamuli and marginal haptoral hooklets, but an adhesive secretion may be involved as well. The parasite causes little damage when attached to thick epithelia, but on the surface of the gill filaments there is erosion and degeneration of the epithelium beneath and adjacent to the haptor. Infiltrating leucocytes enter the dermis, epidermis and the host-parasite interface. Intact infiltrating cell occur in the intestinal caeca of the parasite.

A comparison of the ectoparasite assemblage on snapper, Pagrus auratus, from different regions in Australia and from New Zealand.

Different species dominate the ectoparasite assemblage on P. auratus in Australia and New Zealand, although the same or similar species are available in both countries. The same species of parasite show different patterns of dominance among the same age classes in both countries. Diversity tends to decrease with increase in age class due to an increase in dominance by 1 species. Cluster analysis of per cent similarity data indicate consistent patterns by age class within locality as well as age class among locality. Samples taken a decade apart in the same or nearby locality show a consistent pattern of dominance, diversity and similarity that indicates an overall predictability in the structure of the assemblage within a region.

The rate of development of Polylabroides multispinosus (Monogenea: Microcotylidae) parasitic on the gills of Acanthopagrus australis (Pisces: Sparidae).

Experiments were done to determine the rate of development of Polylabroides multispinosus. Eggs hatch after an average 9, 7 and 6 days at 20, 24 and 28 degrees C, respectively. The ciliated oncomiracidium hatched with one pair of clamps (c.p.). Juvenile worms less than 3 days post-infection (p.i.) had 2 c.p. and blood and hematin in the simple, saccular gut. The gut bifurcated at 11 c.p. (6-9 days p.i.) (24 degrees C). The genital atrium, testes, ovary and vitellaria appeared at 16 c.p. (8-11 days p.i.), 22 c.p. (10-14 days p.i.), 30 c.p. (14-18 days p.i.) and 40 c.p. (17-21 days p.i.), respectively. Eggs were produced at 20 days p.i. The period from egg deposition to egg deposition is about one month at 24 degrees C.

Observations on the pigmentation of the monogeneans, Anoplodiscus spp. (family Anoplodiscidae) in different microhabitats on their sparid teleost hosts.

The monogeneans Anoplodiscus australis and A. cirrusspiralis infect the fins of their respective hosts, the yellowfin bream, Acanthopagrus australis, and the snapper, Pagrus auratus. In these habitats the adult parasite contains melanin-like pigment deposits within the body. Very young parasites lack the pigment but deposits of pigment appear and coalesce into dense deposits within the parasite as it grows. The evidence suggests that the pigment is synthesized within the body of the parasite rather than acquired through feeding on the host epidermis. However, adults of Anoplodiscus cirrusspiralis from the nares of snapper lack this pigment, which suggests that environmental cues may promote the production of pigment as a possible aid to camouflage.

Observations on the attachment by the monogenean, Anoplodiscus australis, to the caudal fin of Acanthopagrus australis.

The unarmed haptor of Anoplodiscus australis erodes the epidermis and attaches to the basal lamina above the stratum compactum in the caudal fin of Acanthopagrus australis by an eosinophilic, weakly PAS-positive and strongly toluidine blue-positive secretion. Ultrastructural evidence shows that the adhesive secretion, in the form of rod-shaped bodies, is produced by subtegumentary cells that connect by ducts to the thin, ventral syncytial tegument of the haptor; these bodies pass into the tegument, then coalesce in the host-parasite interface. This means of attachment has developed by an enhancement and regional specialization of the subtegumentary secretory cells associated with a syncytial tegument in monogeneans and some other platyhelminths. The available evidence indicates that the adult parasite is permanently attached.

Population dynamics of the monogenean Anoplodiscus cirrusspiralis on the snapper, Pagrus auratus.

Populations of Anoplodiscus cirrusspiralis were monitored for 1 year on tagged individual snapper in experimental cages kept in a large on-shore pond with flow-through filtered sea water. The cages were stocked with small and large fish at either low or high initial density. Irrespective of size and density, snapper with light initial infections maintained light infections, whereas fish with heavy initial infections showed fluctuations in parasite population size throughout the year. These data indicate that some snapper have an innate resistance to infection by A. cirrusspiralis, with little evidence for acquired immunity induced by heavy infection. Parasite longevity was greater on the pectoral fin than caudal fin, and greater on large than small fish irrespective of fish density; longevity was greater on susceptible fish than on resistant fish. Recruitment and mortality rates were greater on the pectoral fin and in low density cages, but were influenced by fork length.

Ultrastructure of the protonephridial system, of Anoplodiscus cirrusspiralis (Monogenea Monopisthocotylea).

The flame bulb is formed by a terminal cell and a proximal canal cell. The weir consists of interdigitating ribs all of which form one circle, i.e. alternating ribs do not have distinctly 'internal' or 'external' positions. Cytoplasmic cords are absent and all ribs, i.e. those continuous with the proximal canal cell and those continuous with the terminal cell, form external leptotriches. At least some external leptotriches have interconnected branches extending along the flame bulb. Internal leptotriches are not branched and arise from the basal perikaryon of the terminal cell. In the cytoplasmic cylinder at the tip of the flame bulb, structures resembling incomplete septate junctions were seen. However, neither the cytoplasmic cylinder nor the small protonephridial capillaries contain complete septate junctions as found in all other Monogenea Polyopisthocotylea, Monogenea Monopisthocotylea, Trematoda Aspidogastrea and Trematoda Digenea examined to date. In the lack of a septate junction, Anoplodiscus resembles Udonella, Amphilinidea, Gyrocotylidea and Eucestoda. However, the presence in this species of rudimentary septate junctions in the small capillaries and of complete junctions in larger ones indicates that complete junctions have been secondarily lost. Anoplodiscus resembles the Monogenea and Trematoda in the presence of lamellae in the larger protonephridial ducts. For the first time in a monogenean, the ultrastructure of the excretory bladder is described. A nucleated convoluted duct opens through a narrow connecting duct into the bladder, which in turn opens through a narrow connecting duct into the excretory pore lined by tegument. Convoluted duct, connecting ducts and bladder are lined by a lamellated epitheliu.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of formalin, benzocaine and hyposalinity on the fecundity and viability of Polylabroides multispinosus (Monogenea: Microcotylidae) parasitic on the gills of Acanthopagrus australis (Pisces: Sparidae).

Adult Polylabroides multispinosus exposed in vivo to formalin (200 p.p.m. in sea water, 30 min) deposited a similar number of eggs in 24 h in vitro as did control parasites (sea water, 35 parts per thousand, p.p.t., salinity) and worms exposed in vivo to benzocaine (40 p.p.m. in sea water, 10 min). Worms laid more eggs at 30 p.p.t. salinity in vitro than at 20, 35, 10 and 5 p.p.t. salinity (in decreasing order). Formalin (200 p.p.m., 30 min) decreased the viability of recently laid eggs, the survival of oncomiracidia, removed 70% of juvenile and adult worms from the gills, but decreased only slightly the viability of eggs exposed in utero or after eyespots developed in vitro. Salinities below 30 p.p.t. reduced viability as did an increase in temperature from 24 to 28 degrees C. All adult and juvenile worms were removed by baths in formalin (400 p.p.m., 25 min) or fresh water (1 h).

Extent of gill pathology in the toadfish Tetractenos hamiltoni caused by Naobranchia variabilis (Copepoda: Naobranchiidae).

Sanguinivorous Naobranchia variabilis prefer the first gill arch, external hemibranch and anterior end of the gill arch. The smallest N. variabilis observed attached to fish by a thin filament which connects fused tips of second maxillae to a 'plug' inserted into the gill tissue. Second maxillae enlarge to encircle and increasingly compress the gill filament, which results in a thin layer of epithelium and connective tissue overlying the cartilaginous supporting bar. Early juveniles cause little tissue proliferation, but the extent of proliferated epithelial and connective tissue (PR) adjacent to the maxillae increases from late juveniles to subadult and adult copepods. Most variation in length of gill filament damage (PL, proliferated and compressed tissue) among age classes is explained by maxilla length (ML, length of compressed gill filament); adult trunk width (TRW) explains an extra, small amount of variation, but not trunk length (TRL) or total fish length (TL). Most variation in ML is explained by TRW of adults, subadults and late juveniles, and TRL of early juveniles. PR is explained by TRW for adults, but by ML for other ages. These patterns are due to elongation of the juvenile trunk during growth and lateral expansion of adult egg pouches during maturation. Up to 38 N. variabilis, average (avg.) = 9.3, infected individual Tetractenos hamiltoni and damaged up to 3.4% (avg. 0.72%) of total filament length and 8.6% (avg. 2.1%) of gill filaments per fish.

Observations on the seasonal occurrence of two species of transversotrematid digenea parasitising the sparid fish Acanthopagrus australis in Moreton Bay, eastern Australia.

Ectoparasitic Prototransversotrema steeri Angel infected Acanthopagrus australis (Günther) in western (W. Bay) and southern (S. Bay) Moreton Bay with greatest abundance in winter (June-August), and none in summer (December-February). This confirms previous observations on seasonality of P. steeri from a small estuary in New South Wales. Transversotrema licinum Manter, which is a new host and geographical record, infects A. australis in W. Bay but not S. Bay, with large abundances in summer and winter, lowest abundance in spring. Increased size of P. steeri in winter in S. Bay could be explained by increased size of fish sampled since fish length and size of each parasite species were correlated positively. Transversotrema licinum increased in size from summer to winter irrespective of fish size. Number of eggs in utero and parasite size were correlated for both species; worms in mid-size range had most eggs, and P. steeri had more eggs (average = 19.2, 0-80) than T. licinum (3.3, 0-21); eggs were similar in length. Number of eggs per parasite, adjusted for parasite size, was greatest in autumn (P. steeri) or summer (T. licinum), i.e. early in infection period. Spawning migration to eastern Moreton Bay did not influence number of eggs per parasite.