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<p> Daily ring formation has been validated for a variety of fish species, but there is little known information or data on ageing young of year Alligator Gar (<i>Atractosteus spatula</i>). Artificially spawned Alligator Gar fry with a known spawn date, hatch date, and swim-up date were stocked into two ponds at Tishomingo National Fish Hatchery and reared from 9 to 91 days post-hatch. Up to 10 individuals were sampled each week, and age in days was estimated from counts of presumptive daily rings in the otoliths (sagittae, lapilli, and astericsi). Mean daily ring count and known age were closely related to swim-up (sagitta r² = 0.98, lapillus r² = 0.99, asteriscus r² = 0.93) indicating that daily ring deposition occurred in the otoliths of Alligator Gar 2 days after swim-up. Daily increment counts were accurate through 73 (sagitta), 86 (lapillus), however accuracy for asteriscus was very low throughout 86 days from swim-up. Age-bias plot for the lapillus visually showed no bias between readers. The resulting regression of ring counts against known age (age = -0.96 + 1.03*estimated age) was applied to wild caught Alligator Gar collected in the summer of 2013 from Lake Texoma, Oklahoma, to estimate spawn dates. Spawn dates seem to coincide with rising pool elevation of Lake Texoma and water pulses of tributaries.</p>

In this study, spatial and temporal variation in fat content and temporal variation in maturation of North Sea herring were examined. Fulton’s K, a widely used condition index, was proven to be an inconsistent measure of individual herring fat content, whereas relative condition factor is a more accurate measure.  The Distell fish fatmeter was shown to be an accurate measure of individual herring muscle fat content and was used throughout the study. Individual herring biological and fat data were collected during the annual acoustic North Sea herring survey in 2006 – 2007. Analyses of these data showed that immature herring in the northern North Sea were larger and had higher fat contents than those in the south, in 2006.  This spatial gradient may be due to spatial variability in temperature and food abundance. Individual-level analyses using three years of field data demonstrated that North Sea herring must reach a length threshold of approximately 250 mm before the onset of maturation can occur.  However, stock-level analyses using data provided by the ICES herring stock assessment, indicated that maturation of North Sea herring is not affected by density-dependent factors or by mean North Sea surface temperatures.  This study demonstrates that the accuracy of different measures of condition should be tested before being used in research and that spatial and temporal variability in fat content should be considered when conducting studies on fish condition and other life history parameters.

The copper uptake and toxicity of young and market-size tilapia, Oreochromis niloticus, exposed to copper sulP'hate were investigated. A series of preliminary experiments were conducted to provide requisite information for the final experiment. Preliminary experiments established uptake by the culture systems, feed and/or faeces, and. the impact of fish nutritional state on uptake. Other experiments established the median lethal concentration of copper to this species, an extrapolated minimal lethal concentration, and the optimum exposure duration and concentration for copper uptake. The remaining preliminary experiments defined the relationship between toxicity and uptake in small compared to market-size tilapia, and between muscle location (within the fillet) and copper uptake. The final experiment established the amount of copper uptake in the edible tissue of market-size tilapia after a worst-case exposure to copper sulphate. The worst-case was defined as the maximum non-lethal concentration for a period significantly exceeding that encountered in commercial production systems. The worst-case experiment comprised market-size fish (350 to 570 g) being exposed at a nominal concentration of 365 ppb copper for nine days. This study demonstrated that copper did not accumulate in the edible tissue of tilapia above that measured in non-exposed control fish. A mean level of copper in the edible muscle of non-exposed fish, as measured by atomic absorption spectometry, was 2.14 pprn (dry page weight basis), while in fish exposed to a nominal concentration of 365 ppb of copper it was found to be 2.31 ppm. These data are suitable for incorporation into a United States Food and Drug Administration, New Animal Drug Approval application for the approval of copper sulphate use as a drug for aquatic species.

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