The morphology and ultrastructure of the female reproductive ducts in the metacercaria and adult of Cryptocotyle lingua (Creplin) (Digenea:Heterophyida)

Encysted metacercariae of C. lingua require 38 days in the fish second intermediate host before they are infective to the bird definitive host. Morphogenesis of the metacercaria is arrested shortly after 38 days. The ovary and testes are recognizable at 10 days. By 38 days the lumen of the oviduct is apparent and cilia form on the epithelial lining. The receptaculum seminis remains rudimentary. The cells of the uterine primordium are vacuolated but no lumen is present. Laurer's canal, vitelline glands, and Mehlis's glands are not recognizable. Morphogenesis is resumed in the bird intestine. During day 1 the oviduct and receptaculum seminis complete their development; Laurer's canal and the uterine lumen are formed. During day 2 the cilia in the female ducts become motile and the vitelline and Mehlis's glands are present. Fertilization occurs on day 2 to day 3 and eggs arrive in the uterus on day 3.     

The immune response of the thick-lipped grey mullet, Chelon labrosus (Risso, 1826), to metacercarial infections of Cryptocotyle lingua (Creplin, 1825)

Grey mullet, Chelon labrosus , (60–100 g) have been found to respond immunologically to Cryptocotyle lingua , following a single exposure to 20000 cercariae, by the production of humoral antibody, sensitized pronephric leucocytes and cytotoxic serum factors. Antibody titres measured by passive haemagglutination reached a peak at week 4 with a -log₂ titre of 16±S.E. 1.0, and titres of 10.7±S.E. 1.0 were still recorded after 10 weeks at the termination of the experiment. Cercarial agglutination was found unreliable as a rapid test. Pronephric leucocytes, sensitive to cercarial antigen when measured by the under-agarose migration method, were detected between weeks 1 and 6, peaking at week 2. In vitro polarization was increased when cells were incubated with the antigen, but this increase was not significantly different between control and infected fish. Heat-labile cytotoxic factors of immune sera have been demonstrated to whole cercariae in vitro , these factors being associated with structural damage to the tegument. Pronephros cells isolated from immune fish during each week of infection showed no evidence of adherence to cercariae or metacercariae in vitro. The results are discussed in relation to both host response and course of infection of the parasite.     

Effect of some pharmacological substances on the motility of the Cryptocotyle lingua cercaria (Heterophyidae)

The effect of some biologically active substances (acetylcholine, serotonin, octopamine, sodium nitroprussid and FMRF-amide) on the motility of the Cryptocotyle lingua cercariae was studied. Solutions of FMRF-amide, octopamine, and sodium nitroprussid have no statistically significant influence on the motility of C. lingua. Acetylcholine and serotonin in solutions affected the motility through the prolongation of the active phase of swimming. Further research is required to elucidate the mechanisms underlying the cercarial motility.     

Functional implications of Major Histocompatibility (MH) variation using estuarine fish populations

Recently, there has been a dramatic expansion of studies ofmajor histocompatibility complex (MHC) variation aimed at discoveringfunctional differences in immunity across wild populations ofdiverse vertebrate species. Some species with relatively lowgenetic diversity or under strong directional selection by pathogenshave revealed fascinating cases of MHC allelic disease linkage.More generally in genetically diverse species, however, theselinkages may be hard to find. In this paper, we review approachesfor assessing functional variation in MHC and discuss theirpotential use for discovering smaller-scale intraspecific spatialand temporal patterns of MHC variation. Then, we describe andillustrate an approach using the structural model to producea population composite of variation in antigen-binding regionsby mapping population-specific substitutions onto functionalregions of the molecule. We are producing models of variationin major histocompatibility (MH) loci for populations of non-migratoryfish (killifish, Fundulus heteroclitus) resident at sites thatvary dramatically in environmental quality. We discuss the goalof relating MH population variation to functional differencesin disease susceptibility such as those inferred by observationsof parasitic infection and direct measurement of bacterial challengesin the laboratory. Our study has focused on relatively well-studiedkillifish populations, including those resident in a highlydisturbed, chemically contaminated estuary and nearby less contaminatedsites. Population-specific genetic changes at MHC antigen-bindingloci are described, and evidence relevant to functional implicationsof these changes is reviewed. Population-specific patterns ofvariation in antigen-binding regions in combination with a rangeof assessments of immune function will provide a powerful newapproach to reveal functional changes in MHC.     

Transmission of Cryptocotyle lingua cercariae in natural environments: a field experiment

Atlantic cod were kept at two different depths in three cages placed at increasing distance from a rocky shore where natural infections of the digenean Cryptocotyle lingua occurred in the snail Littorina littorea . During a 6-month period the fish kept at 0–2 m accumulated significantly more parasites than those kept at 2–4 m. Distance from the shore did not affect infection rates. We conclude that host location behaviour of cercariae influences the infection pattern under natural conditions, and that transmission from snail to fish can take place over large areas of coastal waters.     

The effect of Cryptocotyle lingua infection on the blood volume of Littorina littorea

• 1.1. Blood volumes of uninfeeted and parasitized individuals of L. littorea have been measured using inulin dilution.
• 2.2. Uninfected specimens have a blood volume of 64% and parasitized specimens a blood volume of 38% of the flesh weight.
• 3.3. Two different methods of inulin analysis give essentially similar results.

     

Distinguishing trophic and habitat partitioning among sympatric populations of the estuarine fish Osmerus mordax Mitchill

Sympatric populations of rainbow smelt Osmerus mordax of the St Lawrence middle estuary exhibited distinct morphologies suitable for exploiting either pelagic or benthic habitats in the absence of consistent morphological features related to specific diets. The magnitude of morphological differentiation was elevated and constant over 3 years even though statistically significant differences were observed among samples within populations. Both populations were spatially segregated in the estuary but some population mixing occurred at low densities of rainbow smelt. Diet analysis revealed that both populations opportunistically feed on large macrozooplankton. An amended version of Schoener's D was developed and used to compare the magnitude of niche overlap. It revealed that the diet of the middle estuary rainbow smelt differed according to the area where samples were collected but no differences existed between populations. The exploitation of ecologically distinct habitats appeared to be effective in maintaining morphologically distinct sympatric populations within an estuarine setting in the absence of diet differentiation.     

Isolation of infectious pancreatic necrosis virus (serotype Ab) from diverse species of estuarine fish

Two significant fish kills occurred in the Pamlico River estuary (North Carolina, USA), one in December 1981 and January 1982, and the other in June 1982. The first involved only the southern flounder(Paralichthys lethostigma). Histopathologic examination of morbid and moribund flounder revealed extensive sloughing and necrosis of the mucosa of the pyloric caeca and intestine, and inflammation of the submucosa of the pyloric caeca. Brain and internal organ homogenates from morbid and moribund flounder were assayed on CHSE-214 cells, and a virus was isolated. Virus titers ranged from8.4 · 10² to 6.3 · 10⁷ TCID₅₀ per gram of tissue. Cross-plaque neutralization assays indicated that the southern flounder virus was infectious pancreatic necrosis virus serotype Ab. Immersion challenge showed the isolate is only slightly virulent for fry of brook trout(Salvelinus fontinalis). The second fish kill involved the southern flounder and six other species: hogchoker(Trinectes maculatus), Atlantic silverside(Menidia menidia), spot(Leiostomus xanthurus), Atlantic croaker(Micropogon undulatus), silver perch(Bairdiella chrysura), and striped mullet(Mugil cephalus). Virus was isolated from southern founder, hogchoker, Atlantic silverside, and spot. Neutralization assays indicated that the four isolates were nearly identical; however, the diversity of species affected suggests that the virus might not have been the specific cause of mortality.