The ability of thick-lipped grey mullet to mount both humoral and cellular immune responses to Cryptocotyle lingua has been demonstrated here for the first time. Of the 3 procedures for immunisation investigated, namely exposure to live cercariae, intraperitoneal (ip) injection of whole killed cercariae and ip injection of a cercarial sonicate, the former gave the highest primary antibody titres with a peak response at 4 weeks post infection. Peak titres occurred at 5 and 7 weeks after immunisation by ip injection of sonicated cercariae and whole killed cercariae respectively. An enhanced secondary antibody response was observed following challenge by ip injection of sonicated cercariae. Cercariacidal activity, apparently involving complement, was detected in normal serum and enhanced in immune serum. However, the mechanism for complement activation remains uncertain. Parasite antigens were identified following separation by SOS-PAGE and immunoblotting using mullet and rabbit antisera. Mullet failed to respond to certain parasite proteins recognised by rabbit antiserum and in situ immunogold-silver staining demonstrated that mullet. immunised by exposure to live cercariae, were unable to recognise the metacercarial cyst wall. Migration and polarisation of pronephric leucocytes in vitro was enhanced following immunisation but cellular adherence to encysted and unencysted parasites was not observed. In vitro studies further demonstrated a possible role for fish serum in stimulating metacercarial encystment. The intensity of melanisation of the host capsule in metacercarial infections was increased in fish held in total darkness and with increased temperature. The rate of development of the metacercarial tegument and cyst wall and the associated host response was similarly affected by temperature and initial development was inhibited by prior immunisation via ip injection of sonicated cercariae. There was however, no evidence of protection against cercarial infection following such immunisation. These results are discussed in relation to mechanisms of immunity, metacercarial survival strategies and control of metazoan infections in fish.

The principle aim of the study was to evaluate the nutritional value of animal and plant by-products, with the objective of improving the cost effectiveness of diets for culturing seabream (Sparus aurata). The programme of work was initially directed towards applying the current methodology used in fish nutrition research to establish reliable digestibility coefficients for various feed ingredients. A selection of animal and plant materials were tested for digestibility within a reference basal diet designed for seabream. Ingredients for special consideration included poultry by-product meal, feather meal, meat and bone meal, solvent extracted and full fat soyabean meal as well as various other plant derived mater1als. Comparative values for protein, energy and lipid digestibility coefficients were assessed. On the basis of these measurements, experiments were undertaken to evaluate the optimum inclusion levels of promising protein and energy sources as a replacement for the fishmeal component in diets for seabream. Emphasis was made on recent advances in feed processing technology. Raw materials were evaluated in terms of proximate analysis, amino acid profiles and the degree of heat treatment effects on protein quality and availability. Several indices relating to these included lysine availabil1ty, cresol red values and trypsin inhibitor levels for soya products. Growth performance and feed utilization trials were conducted mainly on juvenile fish in recirculation systems under controlled conditions of temperature and salinity. Nutritional parameters such as specific growth rate (SGR), feed efficiency ~FE) and protein utilization parameters were determined 1n each successive trial. The results were favourable with respect to the partial inclusion of animal products in seabream diets. Poultry byproduct meals proved encouraging even at high inclusion levels. The growth performance of fish fed soyabean meal and full fat soya were initially favourable and merited further consideration. These preliminary trials led to a series of practical diet formulations to contain multi-in9redient components, which confirmed previous findings. Var1able results, however, were reported for full fat soyabean meal in this experiment. Finally, the programme of research was presented in the context of the rapidly expanding mariculture industries of southern Europe w1th a particular relevance to Greece.

The role of the lipid-soluble antioxidant α-tocopherol (vitamin E) in the nutrition of African catfish (Clarias gariepinus Burchell) has been investigated with respect to effects on growth, certain indices of health and prevention of tissue lipid peroxidation. Although juvenile C. gariepinus were not found to show an immediate dependency on vitamin E for growth, even during rapid growth stages, a minimum requirement of α-tocopherol based on the prevention of hepatic lipid peroxidation was established at 30-40 mg α-tocopherol per kg dry diet. This is in line with published values for numerous cultured fish species. Tissue α-tocopherol accretion was found to be dependent on dietary dose of the vitamin (supplied as all-rac-α-tocopheryl acetate) and, with the exception of blood-plasma, increased tissue tocopherol status resulted in increased stability against lipid peroxidation. Assessment of iron-ascorbate induced peroxidation (as TBARS) revealed that feeding catfish with diets containing a-tocopherol at several times the currently supplemented level, improved the stability of catfish muscle and this has fillet quality implications. Similarly, heightened fillet vitamin E content resulted in lower moisture exudation from previously frozen fillets, thus demonstrating the role of a-tocopherol in the maintenance of membrane integrity. Oxidation of dietary oils and elevated ingestion of iron were found to be antagonistic of tissue vitamin E concentration. Consumption of feed containing rancid oil had marked effects on tissue fatty acid composition and these effects were modulated by increased intake of α-tocopheryl acetate. In catfish fed diets containing similar amounts of ascorbate, a higher α-tocopherol supplement marginally improved ascorbate retention indicating a possible sparing of vitamin C by vitamin E. The present work will contribute significantly to the understanding of antioxidant nutrition in this poorly researched cultured species. Furthermore, these investigations have improved and strengthened the database of knowledge accumulated within the field of nutrition of finfish.

The prevalence and impact of proliferative kidney disease (PKD) and myxosporidiosis has been investigated in wild fish stocks in the UK, over 1,500 fish representing 17 species being examined. PKD was recorded in brown trout, grayling and pike, the causative agent, the PKX cell, being identified with the aid of light and electron microscopy. A further 27 myxosporean species were also noted, with Myxobolus cotti (syn. M. jiroveci), in the brain of bullheads Cottus gobio being recorded for the first time. Studies on the structure and development of Myxidium lieberkuehni in pike revealed several previously undescribed features. Comparative morphological studies were undertaken to assess affinities of PKX with known myxosporean species. Results indicated similarities with early presporogonic stages of several myxosporean species, especially those belonging to the genus Sphaerospora. The apparent rarity of spore formation associated with PKX infections in the hosts examined focussed attention on species of Sphaerospora as possible sources of infection to salmonids. Studies concentrated on the possible involvement of the 3-spined stickleback, Gasterosteus aculeatus and its renal parasite, Sphaerospora elegans, in PKD transmission. A re-description of this parasite (recently elevated to "type species" for the genus), was prepared. Laboratory experiments using rainbow trout PKX cells successfully transmitted the infection to rainbow trout, brown trout, brook trout and grayling; however sticklebacks challenged with PKX cells did not appear to become infected. Rainbow trout challenged with S. elegans spores and presporogonic stages showed no evidence of sphaerosporosis or PKD. Experiments designed to investigate the possible role of tubificid worms in PKD transmission provided inconclusive results. Field studies provided data on the pathogenesis of PKD in grayling and showed this species to be highly susceptible to the disease.

Given the paucity of information with regards the micronutrient requirements of the currently expanding number of cultured marine species, a series of investigations was undertaken to examine the water-soluble vitamin nutrition of the gilthead seabream (Sparus aurata L.). A preliminary study identified the qualitative requirement of this species for ascorbic acid, the B complex vitamins and choline for the maintenance of health and optimum productivity. Based on the observations of the preliminary experiment, a study was designed which allowed the development of a semi-purified diet and illustrated the qualitative requirement of the gilthead seabream for thiamin, niacin, riboflavin, pyridoxine and pantothenic acid. Using the semi-purified diet, the requirement for niacin and biotin were also established. As one of the vitamins for which the seabream exhibited a strong requirement, pyridoxine was chosen as the focus for an experiment which evaluated the benefit of the incorporation of this vitamin within a practical diet at levels which exceeded the minimum requirement. Thiamin is a vitamin which is known to exhibit a distinct relationship with carbohydrate metabolism, hence this vitamin was chosen as the focus of an investigation of the potential for the modification of vitamin requirements in response to major nutrient supply. Finally, having illustrated the requirement of gilthead seabream growers for ascorbic acid, an experiment was carried out to evaluate the efficacy of a series of vitamin C derivatives as feed supplements for this species. The current series of investigations has not only served to expand the present knowledge of the vitamin nutrition of the target species but has highlighted the potential for novel and applied research which remains within the field of micronutrients.

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