Of 2,122 marine fishes belonging to 36 species collected in the vicinity of Newport, Oregon, 541 belonging to 8 species were infected with hemoflagellates. Four species of trypanosomes and three species of cryptobias were found in offshore fishes, but no hemoflagellates were observed in fishes from Yaquina Bay. Trypanosoma pacifica was found in 177 of 1,102 Parophrys vetulus, 3 of 84 Citharichthys sordidus, and 1 of 35 Lyopsetta exilis, and survived in 10 other species after intraperitoneal injection. The host-specificity observed in nature was probably the result of selective feeding by the leech vector, possibly Oceanobdella sp. or Johanssonia sp. Division stages of T. pacifica were observed in the fish host and described. The growth rate of juvenile P. vetulus injected with T. pacifica was less than that of uninfected individuals for a 10 week period, after which the growth rates of the two groups were equivalent. Trypanosoma gargantua was found in 3 of 7 Raja binoculata and the vector was shown to be the leech Orientobdella sp. Two unidentified trypanosomes were observed, one from 21 of 1,102 P. vetulus, 24 of 303 Eopsetta jordani, and 6 of 61 Microstomus pacificus, and the other from 4 of 35 L. exilis. A small, active cryptobiid was found in 106 of 303 E. jordani, 51 of 1,102 P. vetulus, and a similar but larger flagellate in 9 of 35 L. exilis. After intraperitoneal injection flagellates from E. jordani did not survive in P. vetulus, but did survive in other flatfishes; flagellates from L. exilis survived in P. vetulus, but not E. jordani, indicating the possible presence of two species, one in E. jordani and one in P. vetulus and L. exilis. A larger, sluggish cryptobiid was found in 134 of 1,102 P. vetulus. An extremely large cryptobiid, grossly different morphologically from previously described species, was observed in 1 of 5 Scorpaenichthys marmoratus. The developmental cycle in the leech vector Malmiana sp. was described; the leech Trachelobdella sp. was also shown to be a potential vector. Leeches belonging to the following genera were collected during this study: Johanssonia, two species; Malmiana, three species; Trachelobdella, Oceanobdella, Orientobdella, and Ostreobdella. Of these, one species of Malmiana and one of Orientobdella were experimentally shown to be vectors of hemoflagellates. / Graduation date: 1975

A description of a new strigeid metacercaria of the Neascus group responsible for the production of black spot in the lake shiner, Richardsonius balteatus is given. The metacercaria is distributed over the body in melanistic integumentary cysts. All attempts to obtain the adult flukes by feeding infected fish to pigeons, ducklings, rats, and cats failed. Black spot is erratically though widely distributed throughout British Columbia. Thirty-six of the forty- four lakes examined showed the disease to be present in the shiners. Ptycholeilus oregonensi, Mylocheilus caurinus, Catastomus macrocheilus, Cottus asper, Salvelinus fontinalis, Salmo gairdneri kamloops and Prosopium williamsoni are also infect by black spot. / Science, Faculty of / Zoology, Department of / Graduate

The digenean Stephanochasmus baccatus (Nicoll, 1907) is a parasite found in marine flatfish which are of importance to the mariculture industry in Scotland. In the area of study, Loch Ewe, on the North-west coast of Scotland, the first intermediate hosts are the gastropods Buccinum undatum (L. ) and Neptunea antiqua (L. ). Several species of teleost fish of the Order Heterosomata act as second intermediate host and the definitive host is Eutrigla gurnardus (L. ) or Myoxocephalus scorpius (L. ). Aspects of the host/parasite relationships at all the host levels were investigated. Samples of B. undatum and N. antiqua were collected from May to September and the incidence of the natural infections of the major digenean species were recorded. In some samples, height, weight and copulatory organ length were measured with a view to finding an indicator of parasitism. The histopathology of S. baccatus in the molluscan host was described and seasonal changes discussed in relation to observed variations in the infectivity of cercariae to second intermediate hosts. Groups of 1+ fish were experimentally infected with cercariae at intervals from May to September when no more S. baccatus infections were found in the molluscs. Differences in the infectivity of the cercariae during these months were demonstrated. The pattern of glycogen deposition in both the molluscan digestive gland-and the intra-molluscan larvae were studied in an attempt to explain the loss of infectivity in cercariae in July and August. A. reduction in infectivity of cercariae after ageing was demonstrated experimentally by infecting fish with cercariae which were freshly dissected out and with cercariae kept for 10 hours at 12°C. This loss of infectivity was correlated with loss of glycogen from cercarial tails. A variety of I-group intermediate host species were infected experimentally and the distribution of cysts in the body, fins, skin and muscle were compared with the turbot, Scophthalmus maximus (L. ) and the plaice, Pleuronectes lap tessa L. These were shown to differ significantly. Four species of intermediate host which are of culturable significance, S. maximus, P. platessa, the common. dab, Limanda limanda (L. ) and the Dover sole, Solea solea (L. ) were experimentally infected and the tissue responses to invasion and encystment of S. baccatus were examined sequentially. The inflammatory response and metacercarial growth in each species of fish were found to differ in some important aspects which affected the subsequent viability in the definitive host. The viability of metacercariae from P. platessa and S. maximus were tested by controlled infection of the definitive host M. scorpius. A number of wild caught definitive hosts were examined for natural infections. An attempt gras made to describe the seasonal cycle of events in the life history of S. baccatus based on the information from this and other studies. The relative significance of different host species in different geographic locations was discussed.

Sanguinicola inermis Plehn, 1905, a recently introduced fish pathogen in Britain, has caused considerable damage to the carp industry. Two severely affected fish farms in England were included in the study. The incidence of fish infection for both farms was high, being 74-84% in 0+ and 1+ carp. Studies were made on the infection process and details of route of entry, migration and maturation of the worm are presented. An apharyngeate, furcocercous, lophocercous cercaria which develops in the snail Lymnaea (Radix) peregra (Mü11) was shown experimentally to develop into an adult Sanguinicola inermis. Maximum penetration of cercaria was achieved within 30 minutes and fins appeared to be the preferred site. Large numbers of worms were found to remain in the skin after penetration where they continued to develop to maturity, a previously unreported feature of S. inermis infection. The greatest migration to preferred loci occurred at 60 days post infection immediately prior to egg production. The migratory route used was found to be the loose connective tissue as well as the circulatory system. The distribution of mature worms in major blood vessels changed with season. Light microscopical studies were made on the morphology of specimens collected from the two farms and these were identified as S. inermis. Scanning electron microscopy of the surface topography and transmission electron microscopy revealed details of the tegument and provided evidence for the absence of spines. The major developmental features of the worm are described. A marked increase in size occurred up to 36 hours post penetration. Subsequent growth was slower. Egg production by mature worms began 10 weeks post infection at 15°C. Distribution and development of eggs in tissues is described. Egg production continued throughout the year with peaks during the summer months despite the constant environmental conditions. The growth rate of 0+ fry was studied over a period of 16 weeks and heavily infected fish showed stunted growth and poor Specific Growth Rates, Protein Efficiency Ratios and Food Conversion Ratios. Haematological studies showed that infected fish suffered from hypochromic macrocytic anaemia with leucocytosis and an increased Erkhrocyte Sedimentation Rate. Three different phases of infection were recognized. During phase I, the invasive stage, mortality may occur if infection levels are extremely high, but lightly infected fish present as clinically normal. Phase II was found to be the most critical phase since the majority of fish (over 90%) died at this stage. Histopathology revealed the progress of the infection from cercarial invasion to worm migration, maturation, egg production and miracidial hatching. Pathological changes were observed in the skin in phase I. In phase II, the heart, gills and kidneys were severely affected by both mature worms and developmental stages. The infection reached a chronic stage during phase III evidenced by a granulomatous tissue reaction largely in response to residual eggs in tissues. An attempt was made to integrate the phases of infection, development of the worm and pathogenesis in order to elucidate the host-parasite relationships.

M.Sc. (Zoology) / Please refer to full text to view abstract

Brief history and background of aquaculture and fish health in Sri Lanka In the past, the Sri Lankan fish industry was mainly comprised of capture fisheries, with a heavy dependence on the marine section. Landings from inland fisheries increased enormously following the introduction of the tilapia Oreochromis mossambicus (Peters) in 1952. Sri Lanka has a high potential for the development of freshwater fisheries in its several thousand irrigation reservoirs. Therefore, in the last few decades, attention has been focused on reservoirs mainly for the following reasons; their high potential. there is less cost incurred in their development than in marine fisheries, and because of their great socio-economic importance with regard to food supply and employment opportunities.

No description available.

D.Sc. (Zoology) / Please refer to full text to view abstract

This study investigates the life cycle of Sphaerospora truttae, a myxozoan parasite of the Atlantic salmon, using molecular methods based on the 185 rONA. DNA sequencing showed that the 185 rONA of S. truttae differs substantially from the sequence obtained from its proposed alternate actinosporean life cycle stage, Echinactinomyxon type 5. With more than 90% sequence identity Echinactinomyxon type 5 is closely related to Myxobolus portucalensis whereas S. truttae with an extraordinary long 185 sequence (2541 bp), with inserts in the variable regions of the gene, does not relate closely to any myxozoans. On the basis of the obtained sequence for S. truttae, a single round nested peR assay was developed which allows low-level detection and specific identification of S. truttae in all life cycle stages. Furthermore, two of the primers from the peR assay were successfully used on tissue sections in an optimised in situ hybridisation (ISH) protocol. ISH experimentally identified the gills as the predominant entry locus of S. trottse into the fish host and it detected the spatiotemporal migration of the parasite via the vascular system into the target organ, the kidney. The ISH protocol and the peR assay were also used to screen oligochaetes and other co-occurring invertebrates for S. truttae infection but an alternate host for S. truttse could not be identified. However, 12 actinosporean stages were found and they were characterized on the basis of their 185 rONA, together with 9 further myxosporean species from wild fish in the same riverine habitat. Three actinosporeans were found to be genetically identical with three myxosporeans (Myxidium truttae, Chloromyxum truttse and Chloromyxum sp.) and thus represent alternate life cycle stages of these species. Phlyogenetic analysis of the myxozoans identified a very basal position of S. truttae and S. elegans, as a sister group to the marine species. All other species were nested in the freshwater clades and clustered according to host tissue localization, but independent from host species or myxozoan spore taxonomy.

Dactylogyrus vastator Nybelin, 1924 is a common, economically significant pathogenic monogenean parasite of European carp, Cyprinus carpio L. D. vastator attaches to the gills by means of an attachment organ, the opisthaptor, which carries two large hamuli, a connecting bar and fourteen peripheral marginal hooks. Experiments during the present study have shown that populations of D. vastator on young carp reach peaks of abundance at 12°C, 19°C and 22°C within 5,3 to 4 and 6 weeks, respectively, followed by a decline to a lower level. Parasite abundance was greatest at 19°C and lowest at 12°C. Principal component analysis was used to investigate the effects of temperature on sclerite measurements. It was shown that the basic length and internal root length of the hamuli are the major factors by which populations of the parasite reared under different temperature regimes can be discriminated. Parasites reared at 12°C were clearly separated from those reared at 14°C and 19°C. Scanning and transmission electron microscopic studies were carried out on D. vastator. The outer layer of the epidermis is a syncytial structure. Circular and longitudinal muscle is found beneath this outer layer. The muscle bands are not of uniform thickness. Epidermal secreting cell bodies are located below the muscle layer and communicate with the outer layer via ducts or channels. Possible. epidermal sensillae are unequally distributed over the worm's body. The parasite has four cephalic lobes each of which is provided with a cup-like opening at the border; the unicellular cephalic gland cells empty their contents into a collecting duct. D. vastator shows protandous gonadial development. The female reproductive system has an oval shaped ovary, uterus, ootype, accessory glands, whereas the male reproductive system has a single lobed testis located in the posterior region of the body. Clean sclerites prepared by using an ultrasonication technique were examined under the electron microscope. The hamuli of adult and immature dactylogyrids are divided into internal and external processes and a shaft which ends in a spike. Marginal hooks have a blade and spike. The adult and immature worms can be differentiated by the structure of the auxiliary sclerite. In mature specimens the outer and the inner surfaces of the auxiliary sclerite remain separate. The surface of the hamuli has an interlocking array of striations. The two hamuli are of unequal size in both adult and immature worms. The parasites are not randomly distributed over the gill apparatus. There were no significant differences between gill arches but parasites aggregated in certain areas of the gills, in particular the ventral proximal secondary filaments on both sides of the hemibranch are favoured. Smaller D. vastator which are found in higher numbers on fish presumably represent worms which have recently invaded the host. Larger worms are found in lower numbers. This may be due to competition or an age related mortality in which mature worms die off. D. vastator does not need to be attached to the host tissue to initiate egg laying. In-vitro oviposition was observed and described, however the egg laying rate varies with the environmental temperature. The first eggs that are produced in-vitro are of a large size but as time continues the size of the eggs becomes smaller. A severe hyperplastic tissue response was observed two weeks after the start of an experiment where fish infected with D. vastator were mixed with naive fish. Damage to the host gills caused by D. vastator was observed. Hyperplasia of gill tissue led ultimately to fusion of the secondary lamellae. Affected fish became lethargic and gulped air at the surface. Challenge experiments were carried out to investigate whether there is an acquired immunity by carp to D. vastator infections. The challenged fish had a significantly lower parasite burden compared to the naive fish. The infection causes a change in the blood proteins, as was clearly shown by comparison of infected and uninfected fish, the former having very visibly separable additional bands using gel electrophoresis.