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No / Contrary to some popular thinking, fish do not produce a lot of eggs because so many are eaten by predators. Rather, the rate of predation on fish eggs is high because they produce such a lot of eggs. Many fish produce thousands of minute eggs, each with an infinitesimally small chance of survival because this reproductive strategy in these species results in the highest number surviving to adulthood.

Dietary intake is one of the major routes of human exposure to perfluoroalkyl and/or polyfluoroalkyl substances (PFAS). The objective of this study was to measure perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonic acid (PFHxS) in organic and conventional egg from Sweden (n=8, consisted of 4 pooled eggs and 4 individuals) and China (n=9, consisted of 4 pooled eggs and 5 individuals) and compare the concentrations of PFAS between the two categories (organic and conventional). Also, to evaluate if there was any difference in concentrations of PFAS between both countries. In the end, evaluation of tolerable weekly intake of PFOS and PFOA due to consumption of egg recommended by the European Food Safety Authority (EFSA) was conducted if consuming these eggs would cause any human health risk. Liquid chromatography-mass spectrometry (LC-MS/MS) was used to analyze PFOS, PFOA and PFHxS in the egg samples. In egg samples from China, PFOA was the predominant PFAS; in an organic egg sample from Shenzhen with concentration up to 2000 pg/g, making up to 86% of the 3 PFAS. In contrast, PFOS had the greatest concentration of all PFAS in egg samples from Sweden and was detected in organic egg sample with concentration up to 184 pg/g, making up to 78% of the 3 PFAS. PFOA in samples from China was 18 times higher compared to egg samples to Sweden; results showed no significant differences in PFAS concentrations in egg samples between Sweden and China. In samples from China, concentrations of PFAS had total mean of 50 pg/g for PFOS, 373 pg/g for PFOA and 13 pg/g for PFHxS. In Sweden, mean concentrations of PFOS, PFOA, and PFHxS were found to be 5, 2, and 1,5 times (respectively) higher in organic eggs when compared to conventional. However, significant difference was only observed for PFOS in Swedish organic eggs (p<0.05, t-7.96, df=6). The different concentrations of contamination between organic and conventional egg could be due to the fish powder in organic chicken feed and ingestion of soil through pecking. The result suggests that current concentrations of PFOS and PFOA in organic and conventional chicken eggs are unlikely to cause any immediate harm to Swedish populations. For Chinese population since the consumption of egg has a high risk of exceeding the TWI, the current concentration of PFOA in organic chicken eggs may cause harm to the population based on TWIs established by EFSA. Further investigation is needed with more samples to be analyzed to confirm this point.

Morley, S. A. (1998). Environmental and parental influences on the size of herring larvae. Ph.D. thesis submitted to the University of Liverpool for the degree of Doctor of Philosophy Investigations were carried out into the effects of mean egg dry weight and incubation temperature on the size of larvae from four N.E. Atlantic herring stocks (Buchan, Manx, Clyde and Celtic Sea). Hatching characterisitics (length, weight and yolk volume) of Buchan, Manx and Clyde herring were investigated. The time of hatching was inversely related to incubation temperature, although there was some variation between experiments in the date of peak hatching. The total length of larvae increased through the hatching period. In all experiments mean egg dry weight per female was strongly related to the average length, weight and yolk volume of larvae at hatching. The same regression model could be applied to all stocks. There were, however, stock-specific responses of hatching characteristics to incubation temperature although a reduction in length at hatching at higher temperatures was the most consistent response. Development at low temperature resulted in a modification of the length-weight relationship; larvae of the same weight were longer at lower temperatures. Both the increase in length of larvae during the hatching period and the variation in the timing of peak hatching have implications for the comparison of larvae hatching at different temperatures. The otoliths of Manx herring larvae [from "large" (> 0.33mg mean dry weight) and "small" «0.2Smg mean dry weight) eggs] were marked with either alizarin complexone or calcein so that larvae from pairs of large and small egg batches could be reared under identical conditions (at both 10 and I3.S0C) and relative growth monitored. Within each rearing tank large eggs generally produced larger larvae at hatch (length and weight) with higher growth rates (both weight and length specific). There were significant differences both between eggs from different females and between rearing tanks that confounded the comparisons between rearing temperatures. Fultons Condition factor is not thought to be a good measure of nutritional condition of herring larvae smaller than ISmm total length but may be used as a relative measure of body reserves (ReF) and give an indication of ability to withstand periods of poor feeding. This is indicated by a period of high mortality of larvae hatched from small eggs at 10°C, which corresponded with the time period when these larvae had the lowest body reserves. Video recording of the foraging behaviour of laboratory reared herring larvae was used to investigate differences between the feeding strategies of groups of larvae of the same size but different ages, i.e. fast and slow growers. Slow growing larvae searched larger areas, thus expending more energy, than fast growing larvae, but there was no difference in food acquisition. The difference in behaviour tended to increase through development A simple energetics calculation suggested that approximately 50% of the difference in growth rate could be explained by the extra swimming costs of slower growing larvae. The size of Celtic Sea and Manx herring eggs were experimentally reduced in order to investigate if the volume of yolk in each egg determines the size of hatching larvae. Length at hatch was determined by the volume of yolk in each egg but body weight was not. The development and chemical composition of embryos and larvae needs to be investigated in a further series of experiments. All results are discussed in terms of the influence of larval size on survival.

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One of the major limitations on research into the control of eukaryotic DNA replication has been the lack of any cell-free system that initiates DNA replication in vitro. The first part of the disseration describes the establishment of a eukaryotic system, derived from the activated eggs of the South African clawed toad, Xenopus laevis, that efficiently initiates and completes DNA replication in vitro. Using a variety of biochemical techniques I show that DNA added to the extract in the form of sperm nuclei is efficiently replicated over a period of 4 - 6 hours. Replication of nuclear DNA represents a single round of semiconservative, semidiscon-tinuous replication. The extract will also replicate naked DNA incubated in it, regardless of sequence, though less efficiently than nuclear templates. This is probably related to the unusual ability of the egg extract to assemble apparently normal interphase nuclei from any DNA molecule incubated in it Evidence is presented that initiation, rather than chain elongation, is the rate-limiting step for replication in vitro. In this and in other ways the cell-free system behaves as though it were an early embryo blocked in a single cell cycle. The second part of the dissertation describes experiments that examine the control of DNA replication in the extract The first set of experiments suggest that on replication, DNA is marked in some way so that it can no longer act as a substrate for further initiation. This provides a mechanism by which the template DNA is replicated precisely once per incubation in vitro (or per cell cycle in vivo). The second set of experiments investigate the relationship between nuclear assembly and the initiation of DNA replication in vitro. A novel method for quantifying DNA replication in intact nuclei using the nucleotide analogue biotin-11-dUTP is described. This technique reveals that although they are in the common cytoplasm of the egg extract, different nuclei start to replicate at different times. Entry into S-phase is characterised by a burst of many synchronous or near-synchronous initiations within individual nuclei. This means that nuclei act as independent and integrated units of replication in the cell-free system, and suggests a fundamental role for nuclear assembly in controlling DNA replication in vitro.

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No description available.