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.

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.

The efficacy of the lipid soluble carotenoid astaxanthin (biosynthesised as a secondary metabolite by the microalga Haematococcus pluvialis) as a source of pigment to enhance the aesthetic appeal of the flesh of farmed salmonid species has been investigated, using rainbow trout (Oncorhynchus mykiss) as a model. Accretion of astaxanthin within rainbow trout epaxial white muscle was primarily shown to be dependent on dietary inclusion and the type of diet used as a pigment carrier. Different dietary inclusion rates demonstrated a dose response. Cold pressed low oil and commercially extruded high oil diets containing similar astaxanthin concentration were tested, fish receiving the latter obtained higher growth rates and retained higher concentrations of astaxanthin within their flesh as compared to those receiving the former. Assessment of intact encysted H. pluvialis cells and processed H. pluvialis cells which had been mechanically treated to ruptured their cell wall revealed that the astaxanthin retained within the cells is only bioavailable to rainbow trout when the cell wall has been breached. The carotenoid profile of H. pluvialis confirmed that its astaxanthin was in three forms, i.e. free (5.9%), mono-esterified (82.3%) and di-esterified (11.8 %) to fatty acid moieties. Assessment of H. pluvialis purified mono and di-esterified astaxanthin extracts fed to rainbow trout demonstrated that astaxanthin mono-esters were more bioavailable than di-esters. Image analysis confirmed the major colour component of pigmented rainbow trout fillets is red and the distribution of astaxanthin within fillets varies greatly, with the head region having the lightest hue, which gradually increases towards the tail region. The addition of 2-palmitoylaminoproprionic acid (Corbinol) as a feed additive to diets containing synthetic astaxanthin had no effect on increasing the deposition of astaxanthin in the epaxial white muscle. Nevertheless, none of the in vivo trials incorporating H. pluvialis cells or H. pluvialis derived astaxanthin extracts demonstrated any detrimental effects on rainbow trout, in terms of feed utilisation, growth performance or health. Also, the protection afforded to astaxanthin by ruptured H. pluvialis cysts was demonstrated (during in vitro experiments) to provide increased stability as compared to synthetic astaxanthin, with respect to diet storage, exposure to emulated sunlight and loss in a turbulent water column. The present studies contribute to the awareness of Haematococcus pluvialis as a source of natural astaxanthin for salmonid species, by highlighting both negative and positive aspects with respect to its use in the aquaculture industry.

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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.

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No description available.

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