Reproductive traits, age of female broodfish and aspects of parental behaviour influencing the production and quality of fry in the mouthbrooding tilapia species Oreochromis niloticus and O. mossambicus were investigated. Two incubation containers (conical and round-bottomed) and rearing temperature were first studied to ascertain their effects on egg and fry performance. Partial agitation of eggs in round-bottomed containers significantly (P < 0.05) improved hatchability and success rate of fry production, by 17% and 25%, respectively, compared with conical containers. For the temperature trials only O. niloticus were studied. Two egg acclimation conditions were tested; these influenced the temperature range of hatching, hatching success and the upper and lower median temperature tolerance limits of artificially reared eggs. Thermal tolerance of eggs and fry decreased with progressive development and optimum (> 90%) survival and growth of swim-up fry occurred at 28°-3QoC. Hatching times were inversely related to temperature (P < 0.01) and rates of development to hatching were best described by a curvilinear relationship (P < 0.01). Growth rates, gross yolk utilization efficiency to maximum body weight, age at maximal body weight, onset of exogenous feeding and 50% irreversible starvation (point-of-no- return, PNR) were temperature-dependent. At 24•, 28' and 30' c (xi) maximum body weight occurred on days 18, 9 and 6 post-hatching, respectively, four days earlier than fry at 24' C. Similarly, PNR occurred on days 23, 20 and 18 at 24•, 28• and 30•C, respectively. Reproductive traits of 0+, 1+ and 2+ age-classes of broodfish were investigated. In O. niloticus mean dry egg weight and clutch weight were significantly (P < 0.05) different between all three age-classes, and yearlings produced the smallest eggs, whereas for total and relative fecundity only yearling females were significantly (P < o. 05) different to older broodfish. In both species broodfish age-class had no effect (P > 0.05) on egg:body weight ratio. In both species all reproductive traits were significantly related (P< 0.01) to female age, length and weight. The strongest influences were maternal age on egg size and maternal length and weight on total fecundity and clutch weight. The influence of maternal age and hence egg size on hatching time, and growth, survival, onset of feeding and PNR of fry developing solely on their yolk reserves was investigated. Larger eggs produced longer (P < 0.001) and heavier (P < 0.001) fry which sustained starvation stress longer (P < 0.001). Initial advantages of egg size on growth persisted through to 60 days post-hatching (P <0.05). Feeding success was improved by using of yearlings. For fry from fry from 1+ and 2+ females instead 0+, 1+ and 2+ O. niloticus and O. mossambicus females, PNR was reached on days 9, 12 and 12, and 12, 15 and 18, respectively. Delaying initial feeding beyond six days post-hatching significantly (P < 0.05) reduced the growth of fry. (xii ) Overall survival (between 6-20 days post-hatching) was improved by using older females. The effects of parental breeding behaviour on fry production and quality were investigated. Egg fertilizing capacity of males was inversely related to their number of spawnings in a day. During oral rearing cumulative fry damage increased linearly during the first eight days after spawning and plateaued at 25%-29%. Possible reasons for fry damage are discussed. Naturally reared fry were lighter (P < 0.05) than artificially reared 'siblings'. The implications of broodfish age and size and parental breeding behaviour for mass production of high quality tilapia fry and the need, advantages and feasibility of artificially rearing Oreochromis eggs and fry are discussed.

The relationship between egg size and larval viability, as inferred from size at hatching, resistance to starvation, and growth, was studied in the Medaka, Oryzias latipes (Temminck and Schlegel) , and the Surf Smelt, Hypomesus pretious pretiosus (Girard). Medaka larvae which hatched from heavier eggs were larger at hatching, but did not survive longer during starvation. When the larvae were fed a small and varied food, neither relative growth rate nor relative body depth was correlated with original egg weight. However, when larvae were fed a large mobile prey, Paramecia multimicronucleatum, the larger the egg they came from the faster they grew. Thus, the advantage of large size at hatching is partially a function of the feeding conditions at hatching. In Surf Smelt, egg weight was correlated with maternal age. Two-year-old females produced eggs that were 50% heavier than those of one-year-old females, and hatchlings that were heavier and almost 1 mm longer. Smelt larvae with the most yolk reserve (yolk vol/length) at hatching survived longer, and the amount of reserve was correlated with egg dry weight. The larvae failed to feed in the laboratory. The effect of egg size on larval growth suggests that uncontrolled variation in egg size would affect experimental results, and may be important in commercial fishery management. / Science, Faculty of / Zoology, Department of / Graduate

The first part of this study investigated the effects of varying temperature regimes within the range of 8-22°C on the development and survival of Atlantic salmon (Salmo salar L.) eggs and alevins. The temperature tolerance of eggs was lower than that of alevins: egg mortality increased above 11°C and no eggs survived to eyeing or to hatching at 16 and 14°C, respectively; alevin mortality increased above 16°C and no alevins survived at 22°C. Optimal survivals of eggs and alevins occurred at 8-11°C and 10-14°C, respectively. Subsequent survival at later stages of development was largely determined by survival at earlier stages. Developmental abnormalities among eggs (pin-eyed eggs) and alevins (abnormal hatching and yolk-sac oedema) appeared to be temperature-dependent. Development time in days from fertilisation to eyeing, hatching and maximum alevin wet weight (MAWW) varied inversely with temperature. The sum of degree-days from fertilisation to eyeing and to MAWW was similar at all temperatures, but declined with increasing temperature from eyeing to hatching. The hatching period was similar for all temperatures except 8°C where it was significantly longer. Although alevin size at hatching was not temperature-dependent within the range of 8-12°C, alevin size at MAWW decreased progressively with increasing temperature (10-20°C) during the alevin stage. Fry size at first feeding did not affect their subsequent growth rate or survival. Advanced fry which were fed earliest grew at similar rates to those produced at lower temperatures and attained the greatest weight. Biomass gain was more dependent upon survival than upon mean fish weight. The second part of this study investigated the effects of timing of first feeding on fry growth and survival. Alevins fed prior to final yolk resorption were larger and had lower mortalities than those fed after MAWW. Although the "window" of first feeding opportunity lasted several weeks, delaying feeding beyond MAWW reduced absolute growth. A 5-week delay led to mortalities approaching 60%. However, first feeding can be delayed beyond MAWW for 1-2 weeks at 10°C without adversely affecting subsequent survival or growth rate.

This study was prompted by the need to remedy the situation that existed with respect to the poor status of our knowledge regarding the ichthyoplankton assemblage of the nearshore region along the south-east Cape coast of South Africa. The first chapter provides a brief introduction to the field of ichthyoplankton research and includes a summary of the status of research in southern Africa and an explanation of early life history terminology. The selection of all sample sites, times and strategies is also outlined. The study area along the south-east Cape coast with respect to its location, climate and physical oceanography is described in the second chapter, as is the gear used, bongo nets and an RMT1x6. A sampling protocol for the use of bongos from a small ski-boat, and the RMT from the research vessels, and for the handling and processing of samples was established. The selection of Middlebank as the main monthly sampling site within the Tsitsikamma National Park (TNP) was based on taxonomic diversity as well as logistical and safety constraints. The effect of mesh size and time of sampling with bongo nets on the catchability of ichthyoplankton was investigated in chapter three. Most data was accumulated during Sea Fisheries research cruises, with additional collections coming from the National Parks vessel. Although the differences were not significant, the 505 μ mesh nets captured larger larvae, with catches comprising higher percentages of flexion and postflexion larvae. Larval concentration and size were consistently greater in samples from periods of reduced light intensity, but significant differences were the exception. It was decided that sampling with 505 μ mesh nets during daylight would provide a representative sample of the available ichthyoplankton assemblage, while at the same time being the most practical and least time consuming with respect to handling, clogging and backflushing. In chapter four, the early life history stages of thiny of the seventy-five taxa sampled are described, reflecting the paucity of information which existed on the ichthyoplankton of the nearshore zone in the south-east Cape. These descriptions are seen as an important contribution towards any future research efforts in the region, but as many of these descriptions are based on few or single specimens, it is realised that the description of egg and larval stages will be an ongoing process. Based upon the data collected during this study, an ichthyoplankton species checklist was established in chapter five. Seventy-five taxa of fish larvae were identified to either family, genus or species level. A number of squid para-larvae were also encountered. Similarities and discrepancies with a previous survey in the region are presented. The temporal distribution of eggs and larvae between August 1993 and October 1996 was established, and the spatial distribution of ichthyoplankton along an offshore transect was determined between January 1995 and May 1996. Only 7 species from Middlebank and twelve from all stations combined displayed seasonal trends, with most of these being prevalent during winter months. Egg production, both over Middlebank and from all stations combined, appeared to be consistent, with no seasonal trends. Based upon the results from the offshore transect samples, it would appear that a single ichthyoplankton assemblage exists from Storms River out to fifteen nautical miles. Although a variety of statistical methods were applied to the data during this study, low egg and larval concentrations and a low sampling frequency meant that results had to be interpreted carefully. Chapter six describes the preliminary investigation into the vertical distribution of eggs and larvae. During two research cruises, discrete depth sampling using an RMT1x6 net was performed, with the majority of samples being accompanied by physical data provided by a CTD rosette sampler. No definite patterns could be seen as larval concentrations were low, and the short time scale did not allow for the identification of any diel migratory patterns. The relationship between total larvae and the physical environment was poor. The only possible relationship was that between plankton volume and total egg and total larval concentrations. The TNP may play an important role in the conservation of reef fish and the seeding of nearby fishing grounds through the export of pelagic eggs and larvae. Chapter seven describes a preliminary investigation into the dispersal potential of ichthyoplankton from the TNP. Based upon longshore currents determined from drogues, ADCP vectors and current meter readings, it was clear that if larvae were passive drifters, the potential for their dispersal from the TNP did exist. This pilot study showed that future work should concentrate not only on the oceanographic aspects, but on behavioural aspects of larvae which may enhance or retard dispersal. In the final discussion, it is emphasised that while this study went a long way to increasing our knowledge of the nearshore ichthyoplankton community, the true picture of the temporal and spatial dynamics of the species assemblage may only be revealed once more intensive sampling has been performed. The resolution of the early life history stages of the sparids and the identification of eggs to species level are seen as priorities for the near future. A complete species checklist for the TNP is provided based upon previous surveys (both on adult and larval fishes), this work and personal observations. A total of 171 species of fish from 70 families were identified, illustrating that the eggs and larvae of many species in the TNP have yet to be sampled. A brief description of the collaborative effort which is envisaged for the TNP over the next few years is provided.

Cod hatcheries rely greatly on wild-caught broodstock as egg quality from farm-reared broodstock tends to be poor. Broodstock diet and levels of essential fatty acids have been linked to fecundity and egg quality in cod. Arachidonic acid (ARA) and astaxanthin (Ax) are important nutrients linked to fish egg quality and differences in levels have ben found between eggs from wild and farmed cod. The aim of this thesis was to investigate the impact of dietary supplementation with ARA and Ax on fecundity and egg quality in cod. The first experiment investigated the effect of feeding a diet supplemented with ARA, for 1, 2 or 3 months prior to peak spawning. Results showed that supplementation increased ARA in eggs and that Groups fed the supplement had improved fecundity and egg quality (though with no correlation between the duration of supplementation and number/quality of eggs). The second experiment investigated the effect of supplementation of Ax in broodstock diets on egg quality in farmed cod and showed that Ax was taken up into eggs and that fish fed supplemented diet had improved fecundity and egg quality. The third experiment compared the effect of diet supplementation with ARA and Ax on egg quality in wild and farmed cod and showed that despite the dietary supplementation, wild origin fish performed better on a number of egg quality and fecundity indices. However, it was not possible to take the greater ages and spawning experience of the wild broodstock into account, which may have influenced the results. The fourth experiment measured lipid and fatty acid profiles of eggs from two UK cod hatcheries. Variation was found between farms and across seasons. Results showed that supplementation of cod broodstock diet with ARA and Ax had a positive impact on egg quality and fecundity, although effects were not consistent across all egg quality parameters.

published_or_final_version / abstract / Biological Sciences / Master / Master of Philosophy

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M.Sc. (Zoology) / Please refer to full text to view abstract