Dietary factors are one of the most significant considerations in the regulation of appetite in fish since dietary nutrient and energy concentration modulate feed intake in the short and longer term. These interactions may also be important from a commercial aspect, since the objective of aquaculture is to obtain maximum growth, feed efficiency and consumer acceptance of the product. This thesis addresses the major dietary components which are likely to influence appetite in rainbow trout. These include dietary lipid level, carbohydrate content and degree of complexity as well as energy density and protein/energy ratio. Experimental data is presented which examines the influence of such factors on reed intake, growth performance, nutrient utilisation, gastric evacuation rate, return of appetite and changes with respect to the postprandial level of circulating plasma metabolites. It is proposed that rainbow trout have the capacity to regulate feed intake within specific constraints. On the other hand, trout become obese when offered high oil diets and fail to control feed intake in the short term, possibly due to the palatability of lipids. Regulation may also appear at a metabolic level following accumulation of lipids in adipose tissue. Gastric evacuation rate was probably the main factor in the short term influencing feed intake. This was irrespective of carbohydrate complexity or level in the diet. However, simple sugars might suppress the appetite of trout in the longer term. The biochemical status of liver via plasma glucose concentration may play a more important role compared to gastric fullness in the long- term regulation of appetite. It was postulated that X-radiography was a paramount technique for the quantification of sequential meals and return of appetite measurements in these investigations. The above parameters and their interactions were studied in relation to the physiological control of feed intake in order to develop a more defined model for such processes and to improve the optimum feeding regimes for rainbow trout under intensive production conditions. This is discussed within the wider concept of fish nutrition, and the implications for future research in this area are stated.

The growth of juvenile (0 - III group) C. labrosus, L. aurata and L. ramada was examined in the Tamar, Lynher and Yealm estuaries in south-west England. Two growth models were used to facilitate comparisons among species, age groups and sites of capture. The growth of C. labrosus and L. ramada was similar and faster than that of L. aurata. The growth and relative condition of 0 group fish tended to be greater in St. John's Lake than at other sites, but amongst older fish the reverse appeared to be true. Annual and daily cycles in feeding intensity were examined. A high daily food intake and fast passage of food through the gut appeared to be characteristic of both C. labrosus and L. aurata. In the spring 100% of fish examined were infected w1th cysts of Myxbolus exiguus but this did not appear to have any significant effect on growth or condition. Three 12-15 week feeding experiments were undertaken to examine aspects of the nutrition of I group C. labrosus using experimental diets of semi-purified rations. In the first and second experiments the effect of dietary protein level and ration size on growth was investigated. There was a significant interaction between these factors with optimum dietary protein level decreasing with increase in ration size, and optimum ration decreasing with increase in dietary protein level. In the third experiment the ability of juvenile mullet to utilise dietary energy supplied as either lipid + carbohydrate or mainly carbohydrate in diets containing 20% and 40% protein was examined. Increase in dietary energy resulted in improved growth, but lipid energy had a greater protein sparing effect than carbohydrate energy. The effects of dietary protein and energy level, energy source and ration size on conversion efficiency, assimilation of the diet, histology and size of certain organs, and body composition were also investigated.

Furunculosis is a disease of great economic importance to the salmon fanning industry. The aetiological agent of the disease is Aeromonas salmonicida, probably the most studied pathogen of non mammalian hosts. Little information exists however on the most fundamental aspects of the infection process or the basis of acquired immunity. Although oral vaccination is an ideal solution to the problems of immunising fanned salmonids, poor immunogenicity has always limited the use of this route of administration. In mammals oral vaccination with live auxotrophic mutants has been shown to elicit both humoral and cellular immunity and provide protection against challenge. The recent development of an aroA mutant of A. salmonicida has enabled investigation into the response of rainbow trout to a live oral vaccine. Initially, the role of gastric acidity in the destruction of the live bacteria was investigated in vitro. Aeromonas salmonicida, Yersinia ruckeri and Escherichia coli were compared for acid resistance. Using a system of low pH buffers appropriate to the acidity found in the gut of rainbow trout it was found that A. salmonicida was readily killed by a pH of 4.0 or less. Resistance to low pH increased during stationary phase and 0.002% of bacteria grown for 72 hours were able to survive at least six hours exposure to pH 3.0, compared with 90% of Yersinia ruckeri exposed to the same conditions. The effect of culture medium, oxygen availability, and the pH of the culture medium were also investigated. Whilst growth in BHIB or in a shaking incubator did not alter the resistance of Aeromonas salmonicida to pH 3.0 growth in TSB adjusted to pH 5.5 increased survival of the bacteria by ten fold. It was apparent that the bacteria would probably require protection from the gastric acidity. The uptake and localisation of the bacteria was investigated by recovery and enumeration of viable bacteria from the stomach and intestinal mucus as well as the kidney, spleen and liver of fish vaccinated orally, anally and by IP injection. The presence of the bacteria was monitored between 5 minutes and 72 hours. Bacteria were found in the organs within 5 minutes of delivery regardless of route. The largest numbers were found following IP injection and the lowest following oral intubation. Oral administration of the vaccine protected by prior administration of sodium bicarbonate increased the number of bacteria found in the fish and increased the persistence within the tissues. The effect of growth conditions on the uptake and localisation was also investigated and no increase in uptake was found. Oral delivery of the bacteria in TSB increased the number of bacteria found within the organs to levels above that found following IP injection in TSB. Poor uptake has been reported for killed oral vaccines suggesting that the bacterium was able to invade the host via the gut mucosae. The interaction between trout intestine and A . salmonicida was investigated using TEM and SEM and the ability of the vaccine strain to invade cell monolayers was compared with that of an A-layer deficient strain and Y. rukeri. Infection of the trout intestine in vitro and in vivo led to pathological damage to the epithelium. There was also evidence of phagocyte infiltration and it was apparent that these cells were destroyed by contact with the bacteria. Invasion of tissue culture cells was assessed by acridine orange staining and enumeration of viable internalised bacteria. Aeromonas salmonicida appears to be invasive but its cytotoxic ECPs appear to kill most of the cells it enters. The specific and non-specific humoral immune response to vaccination was investigated. There was evidence of a limited effect on various nonspecific immune response parameters but there was no detectable antibody response to the vaccine. There is evidence that cellular immunity is preferentially stimulated by live vaccines and any future work should involve an investigation of the systemic and mucosal cellular response.

Much attention has been given to the economic aspects of the fisheries in Egypt, while building a statistical or mathematical model for fish production has received little attention. This study is devoted to a comprehensive assessment of Lake Manzala fisheries; past, present and future. Lake Manzala is one of the main fisheries resources in Egypt, and there is evidence that the fisheries have been over-exploited in recent years. The study objectives were to determine the factors that affect fish catches by individual vessels, to compare between parametric and non-parametric models of the fish catches, and to produce a mathematical model of stock behaviour which can be used to suggest policies to manage the Lake Manzala fishery. A new method of estimating the carrying capacity of the lake and intrinsic growth rate of Tilapia and its four species has been developed. Simulation had to be used to get error estimates of the biomass parameter estimates using the new method. Three catch strategies have been investigated and assessed, with discounted utility of future yields. Two ways of modelling individual vessel catches in relation to their effort characteristics, a parametric and non-parametric analysis, have been investigated. Using generalised additive model gave an improved fit to the survey data compared with the parametric analysis. It also gave a lower allowable fleet size which leads to more conservative management policy. A simulation approach was used to investigate the uncertainty in the predicted catches and stock levels, and to give insight into the risks associated with various levels of control. There was no evidence that a management strategy which aimed to fish at maximum sustainable yield would put the stock at risk.

No description available.

The culture of turbot Scophthalmus maximus is currently conducted only in tanks, unlike many pelagic species which are also grown in net cages. Despite the demersal habit of this species, deep pelagic fish tanks are often used with little or no adaptations. A multidisciplinary study was conducted to establish the consequences of several management regimes, primarily a decrease in water depth, on more than a total of 40 biological, water quality and hydrodynamic parameters. Fish fitness, performance and behaviour, exit age distribution, flow visualization, flow velocity determination and water quality determination studies were conducted. Results were discussed in relation to optimal tank management strategies, suitable tank designs, or adaptations to existing designs. A statistical model was proposed. A decrease in water depth from 18 - 9 cm decreased dead volumes from 6.95 - 1.37 1. An increase in depth from 3 - 18 cm increased turbot specific growth rate by 0.44 % day-1 . Tank hydrodynamics had little influence on biological or water quality parameters, despite the large range of water depths relative to the size of the tanks. It was more probable that stocking density and biomass were the major influences on water quality and this in turn may have influenced fish performance. The advantages of reducing water depth in a culture tank were more numerous than the disadvantages.

No description available.

No description available.

No description available.

No description available.