No description available.

For many decades the taxonomy of the genus Dinlostomum von Nordmann, 1832 has remained in a state of confusion in the literature. The present study aimed at determining where the problems lie and what-can be done to resolve them. A brief survey of the farmed and wild populations of fish in Scotland indicated that there were four highly prevalent forms of Diolostomum metacercariae in the eyes of the fish. Type 1 were located in the lens of rainbow trout (Salmo gairdneri Richardson), Type 2 in the humour of rainbow trout, Type 3-in the retina of rainbow trout and Type 4, in the retina of perch (Perca fluviatilis Mitchell). The four types were examined morphmetrically using-Principal Components Analysis (PCA) and this revealed that the four types grouped separately. Type 1 metacercariae could be distinguished by the closeness of their lappets, Type 3 by their small size, Type 4 by their large size and high breadth to length ratio and Type 2 lacked any of these distinguishing features. The culture of the metacercariae to adults revealed biological differences between the four types. Type 1 grew in both domestic chickens and herring gull chicks (Larus argentus Pontoppidan), but best in the latter. Type 2 also grew in both of these hosts, but best growth was achieved in the chicken. Chickens were refractive to Types 3 and 4, but both established and developed in herring gulls. The adults obtained from the bird host were also examined morphometrically using PCA, and again the four forms grouped separately, indicating that they were morphologically distinct. In experimental infections it was found that the hind-body did not fully develop until day 16-18 p. 1. and, therefore, morphological analysis was only carried out on worms which had been cultured in the bird host for more than 16 days. This was particularly significant in Type 1 adults where the relative position of the ovary was affected. Type 1 adults were distinguished from the others by the posterior position of the ovary in the hind-body, Type 2 by the small dimensions of the ovary and its position at the intersegmental region, Type 4 by the anterior extent of the vitellarlum and Type 3 adults lacked any of the distinguishing features. Completion of the life-cycle of the diplostomes also revealed differences in the cercarial stage both morphologically and in the sensory papillar patterns determined by the use of chaetotaxy. The life-cycle was completed for all the diplostomes apart from Type 2. It was found that Type 2 miracidia would not establish in Lvmnaea Dereger, although the other three types established. Infection of fingerling rainbow trout with Types 1,3 and 4 cercariae revealed that the trout were refractive to Type 4 cercariae, but Types 1 and 3 established in the lens and retina, respectively. When perch were exposed to Type 4 cercariae it was found that metacercariae established in the retina. This indicated that the metacercariae are very site specific and also may show some host specificity. Biochemical analysis of the metacercarlae of Types 1-4 by analysing isoenzyme profiles with the use of Isoelectric Focusing (IEF) also revealed that there may also be some differences biochemically between the four types. Identification of the four diplostomes was attempted using the keys (Dubois, 1970; Shigin, 1986) and information available in the literature. However, a confident identification could only be made for Type 1 which keyed down to D. soathaceum sensu Niewiadomska. The other three types could not, however, be identified with such confidence, but tentative identifications were made. The fact that the metacercarial, cercarial and adult stages were obtained and described for three out of the four diplostomes and still a positive identification could not be made perhaps reflects the inadequecies of the keys available in the literature. The present study has successfully determined the problematic areas surrounding the taxonomy of the genus and has, therefore, cleared the way for future study.

No description available.

No description available.

No description available.

No description available.

No description available.

Although considerable evidence exists to suggest that certain populations of scallops, Pecten maximus (L. ) are reproductively isolated, attempts to date to differentiate populations using data from allozyme electrophoresis have been unsuccessful. In order to further investigate the population structure of this species, genetic differentiation was quantified using mitochondrial DNA (mtDNA) markers and the results compared to morphological comparisons and allozyme variation. A multivariate morphological study revealed little variation in shell shape although animals from Brest and La Trinite (Brittany, France) appeared to have longer hinges. A population from Saint Brieuc Bay, Brittany which exhibits differences in reproductive cycle from neighbouring populations could not be separated on the basis of shell shape although unquantified differences in shell colour were noted. Allele frequencies at 7 loci assessed by allozyme electrophoresis were essentially homogeneous throughout the sample range in accord with previous studies and provided little evidence for population subdivision. Length variation of the mtDNA was extensive, therefore variability was assessed through a PCR approach in order that this did not cause analytical problems. On the basis of sequence divergence data there was convincing evidence that P. maximus from Mulroy Bay, Eire, a semi-enclosed sea lough, were genetically differentiated from all other samples. This could not be unequivocally attributed to a reduction in gene flow since the sample consisted of an ongrown single spatfall. Although no distinct pattern of mtDNA haplotype frequencies was apparent, the frequency of the commonest haplotype varied between sites with a pattern similar to that of allozyme allele frequencies in Aequipecten opercularis, a scallop species with a similar distribution and life history for which there is evidence of considerable population subdivision. In comparisons of P. maximus and the closely related P. jacobaeus no consistent differences were detected in morphology, allozymes or mtDNA data. The taxonomic standing of P. jacobaeus is brought into question.

It is confirmed that Mac brachium match r ii contains much lower w3 HUFA levels than marine prawns. For larvae which have a low HUFA profile at stage I. survival and growth vary in relation to dietary linolenic acid which is the precursor of these long chain fatty acids. Diets containing different levels of w6 fatty acids produced large differences in survival and slight differences in growth. Recently hatched larvae utilize saturated and monounsaturated fatty acids for their energy requirements, as PUFA's increase from stage I to stage II, suggesting that larvae are able to chain elongate. Heavier M. n2ank ii females have heavier clutches and higher numbers of eggs. However, female weight does not influence weight per egg, nor the volume of each egg. The length of incubation does not significantly influence the larval survival though a negative trend is observed. The ratio between the weight of the parent female and the weight per egg (Wegg/W) is found to be 0.036 which reflects a poor fecundity. Recently hatched larvae consume microencapsulated feed, but do not survive beyond day 13. However, artificial diets can be fed successfully from stages VI-VII, the best growth occurring at a feeding rate of 8-16mg of microcapsules per litre. For the caridean M. ma br; zi and penaeid a=LtUa m2nQdgn larvae, edge index increases from 641 and 223, respectively, at the beginning of their development to 1847 and 750 at the end, reaching 2817 and 5000 at postlarval metamorphosis. These results confirm the herbivorous, omnivorous and raptorial feeder classification given by Itoh (1970). Recently hatched M. rosenbargii larvae show poor ability to crush their food and rely heavily on their embryonic lipid droplet reserves. Later, they feed on live diets, such as Artamin and rotifers, containing their own enzymes which aid larval digestion. Between stages V and VII, the cardiac foregut becomes muscular, the pyloric filter apparatus is functional, and the hepatopancreas increases rapidly in size. Residence time of food becomes longer in the foregut, but remains the same, and later decreases, in the midget. Survival and growth on artificial feed coincide with these changes, suggesting that larval enzyme production is sufficient to digest and assimilate such diets.

The effects of live foods and microencapsulated diets on growth, survival, body composition and digestive physiology of fish (mirror carp, Cyprinus =LQ) and penaeid shrimp ftna= japQnim) larvae were examined. Raising the lipid content of a microencapsulated enrichment diet from 18.3% to 33.6% improved accumulation of highly unsaturated fatty acids (HUFA) and total lipid in rotifers. Lipids in rotifers were assimilated by carp larvae, as demonstrated by improved growth and accumulation of HUFA in larvae reared on rotifers pre-fed the "high-lipid" diet. Poor diet digestibility coupled with low ingestion rates and low digestive enzyme activity in larvae were identified as contributing to the failure of a microencapsulated diet to support good growth and survival when fed directly to first-feeding carp. Preliminary testing indicates that digestibility of microencapsulated diets for fish larvae can be improved by inclusion of pancreatin. Experiments with Penaeus japonicus indicate that dietary requirements for protein, energy and HUFA by penaeid larvae are lower than previously thought. Foods of low protein content (Chaetoceros gladlia) or low digestibility (microencapsulated diet) elicited high trypsin activity in mysis larvae, compared to those fed Artemia. Larvae receiving both C , gmcilis and Artemi exhibited an intermediate level of trypsin activity - which may explain the superior growth and protein retention in postlarvae reared on the mixed regime. A microencapsulated diet did not support growth and carbon and nitrogen retention equivalent to that in larvae fed live food, despite the strong trypsin response, in mysis larvae. When used together with a low density of _C, p-racilis the microencapsulated diet produced postlarvae of the same size and tissue composition as those reared using live food. It is suggested that the algal co-feed may enhance growth through stimulation of trypsin secretion, supply of extra digestible nutrients or provision of unidentified specific growth enhancing factor(s).