In vivo experiments were conducted to examine the haematology of juveniles from two relic bony fishes, Atlantic sturgeon Acipenser oxyrhinchus and shortnose sturgeon Acipenser brevirostrum. Oxygen transport characteristics (haematocrit, haemoglobin and mean erythrocytic haemoglobin concentration), ionic composition (Na þ , Cl À , K þ and osmolality), metabolite concentration (lactate, cortisol and glucose) and protein content in blood were measured or calculated at rest and during recovery from forced activity. Under resting conditions, plasma osmolality and concentrations of Na þ , Cl À , lactate, cortisol and total protein were significantly different between Atlantic and shortnose sturgeon. All other resting variables were not different between species. Following forced activity, plasma lactate levels were significantly higher in both species than at rest. Plasma cortisol levels in both species were only significantly higher 1 h following forced activity compared to resting values. Plasma lactate levels were significantly higher in Atlantic sturgeon than in shortnose sturgeon, but these levels returned to resting levels by 1 h in both species. Cortisol increases were greater in shortnose sturgeon than in Atlantic sturgeon. In general, oxygen transport characteristics, blood glucose, plasma protein and plasma osmolality were not altered by forced activity in either sturgeon species. Overall, both species had reduced responses (i.e. the magnitude of changes in measured variables) to forced activity compared with teleosts. # 2005 The Fisheries Society of the British Isles
Introduction 142Abundance-area relationships 142Habitat specific -total population growth relationship 144Commonality in spatial dynamic models 145Does density-dependent habitat selection exist in marine fish? 148Effect of spatial scale 149
Conclusion 150Acknowledgements 150References 151Abstract Current methods and theory used in the study of the spatial dynamics of marine fish are problematic. Positive relationships between population abundance and occupied area are typically interpreted as evidence of density-dependent habitat selection. However, both abundance and area may co-vary with an un-parameterized variable, such as a density-independent effect. In addition, if density-dependent habitat selection is present, population growth rates in optimal habitats would be expected to be lower than in marginal habitats. This same pattern can also evolve from a largescale, spatially autocorrelated change in a density-independent factor. The theory underlying density-dependent habitat selection, the ideal free distribution, can be tautological when no a priori information of how habitat suitability changes with density is known. In this case, an ideal free distribution can be defined for any pattern of habitat-specific population growth rates. However, these problems are not insurmountable and solutions may be found by considering spatial variation in proxies of fitness and explicitly allowing for the relative importance of habitat selection (density dependent) and environmental (density independent) effects to vary with spatial scale.
A significantly greater proportion of Atlantic cod (Gadus morhua) sperm were motile in the presence of ovarian fluid and egg compared with seawater. Sperm mean and maximum swimming speeds were also significantly greater in the presence of ovarian fluid and egg compared with seawater. However, there was no significant difference in path linearity among treatments. We also examined the interaction between maternal stimuli (egg and ovarian fluid), time sperm spent in seawater prior to exposure to each stimulus, and salinity on proportion of motile sperm and their swimming behaviours. Proportion of motile sperm decreased significantly with a decrease in salinity in the presence of both maternal stimuli. Proportion of motile sperm also decreased with time spent in seawater prior to exposure to ovarian fluid but not to an egg. Both mean and maximum swimming speeds were maintained in the salinity range of 20-30 ppt and only declined significantly at lower salinities (15 and 17.5 ppt). Mean and maximum swimming speeds decreased with time spent in seawater. This study demonstrates the importance of maternal factors when examining sperm swimming behaviour and highlights the significance of maternal-paternal gametic interactions in understanding fertilization success.
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