This Phd thesis presents an extensive investigation of the kinetic behaviour of oxolinic acid (OA) and oxytetracycline (OTC) in Gilthead Sea Bream (GSB) ("Sparus aurata" L.) and Sharpsnout Sea Bream (SSB) ("Diplodus puntazzo" Cetti, 1777) at 19-20[sup]oC. The distribution half-life (t[sub]1/2[alpha]) and the elimination half-life (t[sub]/2[beta]) of OA from GSB plasma were found to be short (0.5 and 12h respectively) while longer values were estimated for OTC (2 and 53h respectively). Similarly, in SSB, calculated t[sub]1/2[alpha] and t[sub]1/2[beta] revealed values of 0.4 and 10h, respectively. The corresponding values for OTC were 1.4 and 34h. The apparent volume of distribution at steady-state (V[sub]d(ss)) of OA was identical in the two species (2Ikg[sup]-1). Higher V[sub]d(ss) values of OTC were found in both sparids (2.9 and 4lkg[sup]-1 for GSB and SSB, respectively). The bioavailabilities (F%) of OA and OTC following oral administration were found to be low in GSB (14 and 9% respectively). In SSB, the F of OA was calculated to be 15% while absorption of OTC was totally inhibited. The apparent digestibility of OTC was determined to be 27% in GSB and 40% SSB. However, the apparent digestibility of OA in both fish was considerably higher (92%; GSB, 88%; SSB). The tissue distribution and residue depletion of OA in both sparids revealed that OA is eliminated from edible tissues rapidly, allowing short withdrawal times. Short and long withdrawal times for OA and OTC respectively, are shown in this work to be necessary for safe human consumption of treated fish. All experiments in this work indicated reduced absorption of both drugs, which would result in significant release of the drugs in the vicinity of aquatic farms using sparids. This poses an environmental concern because of the potentially rapid development of a resistant aquatic bacterial population and possible adverse effects for other organisms in the habitat. Also there are potential financial losses associated with drug losses to the environment. Therefore, low drug absorption is clearly undesirable and studies to improve their absorption in sparids for future therapies is of vital importance.

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The study objectives are: (i) to describe the settlement and household conditions and activities in the coastal area of Pakistan; (ii) to analyse the current behaviour of shrimp fishermen, and to describe the shrimp marketing system, and government policy towards the shrimp fisheries sector; (iii) to compare the current technology and economics of Pakistani shrimp farming with those of other shrimp-producing countries; (iv) to identify the scope for the future development of shrimp farming in Pakistan and the implications for fishermen households; and (v) to assess the future overall economic viability of the Pakistan shrimp farming sector. The research comprises: (a) a survey of current shrimp fishing in Pakistan; (b) reviews of shrimp farming in major producing countries; (c) budget analyses and linear program modelling of shrimp and other household enterprises, and (d) cost-benefit, financial, sensitivity, and policy analysis of shrimp farming in Pakistan. The conclusions/results include: (i)  Shrimp fishermen households in Pakistan have experienced a downward trend in their living standards over the last two decades due to over-exploitation of wild shrimp. (ii)  Good prospects for Pakistan farmed shrimp exist on the world market. (iii)  Suitable land is available, and a government-sponsored shrimp hatchery has started work to provide postlarvae. (iv)  Shrimp fishing households could reallocate their labour and other resources towards shrimp farming and thus be able to reap substantial amount of net benefits. (v)  Shrimp farming is economically viable along the Pakistani coastline. (vi)  Awareness of opportunities for shrimp farming on a modern technical, environmentally friendly and sustainable basis should be disseminated in the coastal areas of Pakistan. (vii)  Government assistance in the farm land allocation and institutional credit will be necessary help to boost the shrimp farming industry in the coastal areas.

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This research programme aimed to review the nutritional requirements for the main minerals, (namely calcium, phosphorus, magnesium and zinc) formulated in commercial diets that are essential for the health and growth performance for salmonid fish. This was undertaken with the aim of improving our knowledge of their physiology, metabolism and fate in the rainbow trout, Oncorhynchus mykiss. Phosphorous (P) featured strongly in this work due to its adverse role in pollution and the environmental impact of intensive fish farming. The first chapter surveyed the gross nutritional requirements of fish and focused on the mineral requirements in particular. Typically the P requirements for trout were found to range from 0.5-0.8% of the diet. The problems of P loading as a consequence of dietary loses was addressed and the physiological and metabolic roles of both calcium and phosphorous were especially noted in relation to fish health and for phosphorous its environmental implications were addressed. Experimental approaches were evaluated and it was decided to conduct both standard growth trial studies as well as digestibility trials to provide the basis of most investigations with the rainbow trout. Novel approaches and strategies were used in relation to specific experiments such as examining the mineral levels in blood, and various tissues and the testing of different feed ingredients, dietary supplements and mineral sources in successive investigations. Initial investigations appraised commercial diets of varying nutritional profile with respect to mineral retention and availability for rainbow trout under controlled laboratory conditions. The effects of diets containing different fishmeal sources: i.e. brown versus white fishmeals, elevated ash content and also varying in the levels of oil were tested on juvenile rainbow trout in closed recirculated systems. Diet composition caused a significant effect on mineral retention and distribution profile in fish tissues and organs. Typically, both P and Ca were of highest concentration in vertebrae of trout (60mg/g-dry weight), compared with P concentrations for all other major organs/tissues, which were fairly even between 11-20mg/g. A small increase in dietary P level (1.08% vs. 1.22%) did not affect any growth parameters for trout for the first two commercial feeds tested but there were interesting observations with respect to the amount of P excreted in the bile with a 25% increase from 0.8mM to 1.2mM. The P levels in plasma of these fish did not reflect any dietary changes. However, there was a noticeable reduction in the digestibility of P in the diet containing the white fishmeal source (26%) compared with 49% for the higher grade fishmeal diet. High ash content feeds resulted in a marked reduction in the net mineral retention of this element (16% compared to 27% for the lower ash diet). The same was also true for Ca (12% compared with 26%). The effect of oil levels in diets on mineral utilization was investigated under farmed conditions and was of particular interest given the demand for nutrient dense feeds in the industry. There was a strong tendency for improved P and Ca digestibility coefficients at each incremental increase in oil level for juvenile production sized fish (50-l00g). This ranged from 55% to over 70% when oil levels were over 26%. However this was not observed for larger fish of over 200g in weight. Experimental investigations followed are described in (Chapter 4) where fishmeal based diet was supplemented with varying levels of inorganic phosphorous. Phosphorous, calcium and other mineral absorption characteristics in addition to retention were measured in a series of growth and digestibility trials. Interestingly, there was no apparent change in the distribution of P with increasing dietary levels ranging from 1.39-2.16%. These were above known requirements for these fish with minerals being in excess. Similar results were noted for all other minerals measured in rainbow trout. There was a significant rise in the P concentration of plasma of rainbow trout fed a diet containing over 2% P and this may infer that the homeostatic regulation of P is unable to function at this level. Other haemato-logical parameters were not affected. Although not significant, there appeared to be slight trend in elevated bile P with increasing dietary P supplementation. The faecal concentrations for each of the minerals showed that elevated P in fish meal diets led to increased faecal output from 25mg/g to over 40mg/g for the highest P diet. Overall digestibility coefficients were lower as dietary P increased above that in the fishmeal control diet. These ranged from 50% to 39% for P, Ca and Mg were not greatly affected. The net retention of P was calculated and this fell from 30% to just below 20% for the range of dietary P used in the investigation. A preliminary study, reported in chapter 5A, was useful in providing information about the relative absorption profiles for differential mineral absorption from the various regions of the gastro intestinal tract of rainbow trout. A standard commercial diet was fed to large trout (>200g) and subsequently, digesta was removed from fish and analysed. For all minerals and protein, the pyloric and mid intestinal region was the main site for digestion, release and absorption of the macro elements concerned. The protein and mineral digestibility of suitable feedstuffs commonly employed in the formulation of complete diets for trout resulting from a sequence of experimental trials are presented in chapter 5B. These included a selection of marine, animal and plant by-products which were substituted into a reference basal diet designed for salmonids. This involved the inert marker- yttrium oxide and calculations based on nutrient digestibility from diet and faecal concentrations. Mineral digestibility coefficients were found to vary considerably and a number of anomalies such as negative values were obtained for Ca and Zn in certain feedstuffs. Combined diets (reference and test ingredient) gave values that were more consistent and P digestibility ranged from 47-59% in marine and animal protein concentrates compared with plant sources (24-37%). Negative values for Ca and Zn were thought to be attributable to complex interactions with other feed components. Additionally, a group of inorganic mineral supplements were tested by inclusion into a series of diets. These included mono calcium phosphate, di-calcium phosphate (DCP), mono di-calcium phosphate and magnesium phosphate. DCP produced lower Ca and P digestibility values, 31 and 50% respectively, compared with the other sources (44-62%), indicating the importance of choice of mineral supplement in aquafeeds. A critical appraisal of this work is provided in Chapter 6 and formed a retrospective review of the results generated and integrated these findings into a foundation for further research and development. Nutritional investigations using the rainbow trout as the model salmonid species raised many more questions and possibilities and broadened the scope of the topic. The subject of mineral requirements for fish is very complex and numerous factors are involved at several physiological and biochemical levels in fish. Although the research on rainbow trout involved whole animal studies under both laboratory and commercial farm conditions, the need to explore alternative in vitro methods and to utilize larger scale farm and sea cage trials for salmon were suggested. The advent of more advanced diet formulations and feeding strategies were mentioned and the scope for more scientific investigations to improve the utilization and reduce phosphorous discharge into the environment proposed.

Interpreting data gathered from field studies that investigate the effect of pollution on fish parasites is complicated by the presence of multiple parasite species and mixed pollutant loads. The aim of this study was, therefore, to use controlled experimental studies to assess the impact of a single heavy metal, cadmium, on selected species of the monogenean genera, Dactylogyrus Diesing, 1850 and Gyrodactylus von Nordmann, 1832 and on their hosts, Cyprinus carpio L. and Poecilia reticulata (Peters). The first host-monogenean system investigated was the gill fluke Dactylogyrus extensus Mueller & Van Cleave, 1932 and its host C. carpio; the second system, Gyrodactylus - P. reticulata, involved individual investigations on Gyrodactylus turnbulli Harris, 1986 and G. bullatarudis Turnbull, 1956. Independent investigations of parasite biology and host responses were undertaken in order to elucidate host-parasite interactions in the presence of cadmium. The maximum permitted level of cadmium in controlled freshwater sources is set at 5μg/l by EEC Directive 76/464/EEC and experiments were carried out using this concentration and the higher, but environmentally realistic, levels of 20-50μg/l. For the first time it has been demonstrated that Dactylogyrus extensus exposed to 5μg/l cadmium show a subtle enhancement in the in vitro rate of oviposition and a statistically significant enhancement in their in vivo rate of oviposition after 9-10 days exposure. The effect of cadmium on egg production by D. extensus and on selected aspects of the innate immune response of C. carpio were investigated in separate experiments. Although run independently of each other, the sample times of both experiments were the same. It was found that the treatment in which the rate of oviposition by the parasite was greatest, was the treatment, where at the same sample point, the phagocytic activity of C. carpio was greatest. Exposure of D. extensus to the higher level of 30μg/l cadmium, also enhanced egg production after 9 days, but, 14-30 days exposure resulted in a lower rate of oviposition than that recorded in control parasites, suggesting that cadmium may directly, as well as indirectly, influence the reproductive biology of this parasite species. The hatching of D. extensus eggs was similarly affected by cadmium exposure, with those produced and incubated in 5μg/l cadmium demonstrating a statistically significant more rapid hatch rate than the controls, while those produced and incubated at the higher concentration (30μg/l) showed a statistically significant slower rate of hatch than the controls. Exposure of adult D. extensus to cadmium concentrations ranging from 5 to 3,400μg/l in vitro resulted in an enhancement of survival above the controls. Only at 13,100μg/l cadmium was there a statistically significant reduction in survival and in vitro egg production. Atomic adsorption spectrometry demonstrated that D. extensus is a net accumulator of cadmium, with the concentration of cadmium accumulated by the parasite, increasing with increasing exposure concentrations. The degree of cadmium accumulation in C. carpio organs was in the order of gills > kidney > liver > muscle=spleen. Even at 5μg/l, the level of cadmium detected in the muscle (ca. 0.2μg/g) exceeded the permitted level in food fish (0.05 mg/kg (μg/g), after only 9 days exposure. The haematological and immunological responses of C. carpio exposed to 5μg/l cadmium showed only subtle differences from the control fish, with these differences being most marked in the early stages of the trial (days 9-14). By the end of the trial there was little difference in the responses of these fish from the controls, suggesting that carp can adapt to low-level cadmium exposure. Cadmium at 50μg/l resulted in exaggerated alterations to the immune responses of carp, with statistically higher cortisol levels, phagocytic activity of kidney phagocytes, granulocyte number and significant lymphopenia, at days 6 to 14 of the trial. Several of these changes are indicative of a typical stress response. The respiratory burst and phagocytosis of kidney phagocytes in C. carpio appear to be linked to the level of cortisol, with both factors increasing as cortisol levels fall, suggesting that the effects of cadmium on the immune system may be mediated to some extent via the production of corticosteroids. Cadmium at concentrations below the permitted maximum caused statistically significant increases in the population size of both Gyrodactylus bullatarudis Turnbull, 1956 and G. turnbulli Harris, 1986 on P. reticulata. Statistically significant differences in the population size of G. turnbulli were also recorded between male and female P. reticulata. Exposing P. reticulata to 5μg/l cadmium resulted in little difference in the respiratory burst of kidney phagocytes and the production of myeloperoxidase when compared to the same parameters in control fish. The phagocytic activity of these fish was, however, consistently elevated above the controls. Exposure to 20μg/l cadmium resulted in a further enhancement of both phagocytosis and respiratory burst in P. reticulata. Unlike, C. carpio, no adaptation to cadmium exposure was observed in P. reticulata within a 30-day period. During the trial, subtle differences in the innate immune parameters of male and female guppies also emerged. None of the three innate immune parameters investigated, i. e. phagocytic activity, respiratory burst and myeloperoxidase production, appeared to correlate to the observed differences in the population growth of G. turnbulli. The finding that cadmium at levels below its permitted maximum can significantly increase numbers of Gyrodactylus spp. to the detriment of P. reticulata, suggests that the water quality guidelines, with regard to the permitted concentration of this metal, should be reviewed. This study has provided the first information on the effects of low concentrations of cadmium on selected monogenean parasites and their hosts and has been the first to attempt to elucidate host-parasite interactions in the presence of this metal. The study has provided a range of interesting findings and has offered several avenues for further investigations into a complex field of research that is still in its infancy.

No description available.

No description available.

No description available.