Annual pattern of brooding and settlement in a population of the flat oyster Ostrea chilensis from central New Zealand

Temporal patterns of larval brooding and settlement were investigated in a flat oyster (Ostrea chilensis) population in Tasman Bay, central New Zealand. The proportion of the population brooding larvae and larval settlement rates were monitored over 26 months. A peak period of brooding activity began in late spring and continued through summer. Maximum rates of 17% and 23% of adult oysters brooding larvae occurred in November and December, and an estimated 55–78% of adult oysters incubated larvae over the entire summer breeding period. These proportions of brooders are higher than those previously reported for Tasman Bay. A very low level of brooding activity (1%) occurred during winter. Temporal trends in larval settlement closely tracked brooding patterns. Settlement was greatest between November and January, and there were very low rates in winter. The seasonal breeding pattern in the population was intermediate between northern and southern populations, confirming a latitudinal gradient of reproductive behaviour for O. chilensis in New Zealand. Results are useful in optimising the timing of substrate deployment in an enhancement programme for the oyster fishery.     

Age and growth of bluenose,Hyperoglyphe antarctica (Pisces: Stromateoidei) from the lower east coast,North Island,New Zealand

Growth of the bluenose, Hyperoglyphe antarctica (Carmichael, 1818) from the lower east coast, North Island, was determined by counting growth check rings in otoliths. One growth check ring appeared to be laid down each year, so this technique is probably valid for aging bluenose. Female fish had a significantly higher growth rate than males. Comparisons of samples from three sites indicated no significant regional differences in growth. The von Bertalanffy parameters L8,K, and t0 fitted to back‐calculated fish lengths were, respectively, 81.1 cm, 0.308, ‐0.627 for males, and 86.1 cm, 0.308, ‐0.384 for females.     

西埔湾港养黄鳍鲷年龄、生长和食性研究

本文研究了福建省东山县西埔湾港养黄鳍鲷鳞片年轮特征、渔获年龄组成和体长组成,并结合生物学资料,对其体长与鳞长、体长与体重及其食性作了分析。食料生物类群比较广泛,消化器官结构与其食性相互适应,系属于底栖生物食性类型的低级肉食性鱼类。文中还讨论了西埔湾黄鳍鲷资源合理利用和繁殖保护问题。     

Validation of growth zone deposition rate in otoliths and scales of flathead mullet Mugil cephalus and freshwater mullet Myxus capensis from fish of known age

Flathead mullet Mugil cephalus and freshwater mullet Myxus capensis are important components in South African estuarine fish communities and fisheries, but there is little information on their age and growth or age validation. This study validated the periodicity of growth zone formation in sectioned sagittal otoliths and scales of fish of known age that had been at liberty for 10 years. For both M. cephalus and M. capensis, the number of growth zones counted on otolith sections did not differ significantly from the known age of the fish. There were significantly fewer growth zones on scales than the known age of both M. cephalus and M. capensis. Growth zone deposition rate could therefore be validated as annual for otoliths but not for scales of the two species. It is recommended that future ageing studies focus on otoliths rather than scales.     

Spatial variability in growth and reproduction of the Pacific oyster Crassostrea gigas (Thunberg, 1793) along the west European coast

The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion.     

Seasonal variation in the reproductive activity and biochemical composition of the Pacific oyster (Crassostrea gigas) from the Marlborough Sounds,New Zealand

Reproductive cycles of the Pacific oyster Crassostrea gigas (Thunberg) from the Marlborough Sounds, New Zealand, were followed between June 1998 and January 2000. Histological examination of the gonad confirms an annual cycle with a winter inactive period followed by rapid gonad development and a single short spawning period. The population gonad index correlated with seawater temperature and changes in tissue dry weight, condition index, and biochemical components. In winter, few individuals with early gametogenic stages were present and rapid development of primary oocytes (diam. 11 μm) occurred during spring (September‐November). The developmental rate and the diameter of mature oocytes (37 μm) was similar for the 1998 and 1999 seasons. For a standard 110‐mm‐length oyster, maximal tissue body weight and condition index were recorded in December. Rapid weight loss in January was length dependent and was attributed to spawning. Temperature was the environmental variable which best correlated with the timing of gametogenesis. Food availability (phytoplankton biomass) may have been responsible for inter‐annual variations. The biochemical composition (% glycogen, lipid, protein) of separated gonad and somatic tissues were variable seasonally and annually. Gametogenesis (oocyte diameter) was associated with increased gonad protein and glycogen and a decrease in lipid concentrations. These changes are similar to those in Pacific oyster populations from other parts of the world.     

南黄海牡蛎壳元素组成的原位微区分析及环境指示

碳酸盐生物壳体的周期性生长纹层是记录气候环境变化的天然材料。随着原位微区测试技术的快速发展,高分辨率的同位素和化学元素组成的快速分析显著推动了古气候环境变化及生物地球化学研究。应用激光剥蚀等离子体质谱仪（LA-ICP-MS）对南黄海现代牡蛎Crassostrea gigas壳体韧带部的元素组成进行原位微区测试,利用内标元素43Ca进行元素比值的校正,探讨了牡蛎壳中化学元素特征及其环境意义。研究的长牡蛎壳体中Mg/Ca、Sr/Ca、Na/Ca比值具有显著的季节性周期变化。环境水体物理化学性质的变化对壳体生长速率影响较大,壳中白垩质方解石和叶片方解石生长层分别对应较高和较低的环境温度,白垩方解石层具有较高的Mg/Ca、Sr/Ca和较低的Na/Ca比值。Mg/Ca比值可指示牡蛎壳体生长环境水体温度,利用前人Mg/Ca比值公式计算可以恢复与器测资料相符的近岸海水温度结果。本研究对应用LA-ICP-MS分析技术开展高分辨率的生物壳体元素组成和环境示踪研究具有借鉴意义。