Studies on twelve common bivalve larvae,with notes on bivalve spawning seasons in New Zealand

Twelve common bivalve larvae occurring in the plankton from the Bay of Islands (35°15'S, 174°10'E), Wellington Harbour (41°16'S, 174°51'E), and off Raumati Beach (40°56'S, 174°58'E), New Zealand, during 1970–72 are described and, wherever possible, provisionally identified. The seasonal occurrences of these larvae in the plankton are also described. Information on the spawning cycles of some New Zealand adult bivalves is reviewed; although some species have a short (4 months or less) spawning season, for most it is much longer, possibly with ‘trickle’ spawning through several months of the year.     

Reproductive biology of horse mackerel Trachurus capensis and Trachurus trecae in Namibia and Angola

Harvest control measures for Namibia and Angola are defined using reference points for spawning biomass, which requires knowledge of spawning potential and dynamics of fishery stocks. The reproductive biology of two species of horse mackerel, Trachurus capensis and Trachurus trecae, in these waters was investigated for spawning distribution in time and space. Samples were collected during two scientific cruises conducted in February and July/August 2007 off the coast of Namibia and Angola. A total of 396 fish ovaries was examined to determine the spawning dynamics of the two species. The ovaries were histologically analysed and their oocyte distributions mapped. The length (TL)–weight relationships of the two species differed significantly. The observed development of oocyte recruitment and absence of a hiatus in the oocyte distribution indicated that these species are indeterminate spawners. Analyses of the data from the NatMIRC database (2001–2004) indicated annual changes in gonadosomatic index (GSI) for T. capensis at different latitudes, but these changes were small. GSI also fluctuated between years and areas, but there were no clear spatial or temporal trends, with averages ≤4.0% at all stations. The GSI of both species was not indicative of the histologically determined development of gonad maturity. Oocyte maturation for T. capensis indicated that smaller and younger fish spawn first. Batch fecundity (F) for T. trecae was best described by F = 4 986 TL (cm) – 99 645 (r ² = 0.83). This study provided the first analyses of oocyte development in time and space for the two species in the region.     

Development of a sound reflection system for profiling sediments in shelf and slope depths

A sound reflection system for obtaining profiles of sedimentary structures in shelf and slope depths to 500 m has been developed, based on an Edgerton 1 kJ boomer as sound source. A logarithmic response receiver allows optimal recording of signals over a wide dynamic range. Penetrations of up to 500 m have been obtained from structures within both unconsolidated sediments and folded lower Tertiary structures. The equipment works reliably at speeds up to 9 knots.     

Gametogenic development and spawning of the razor clam,Zenatia acinaces in northeastern New Zealand

The potential exists for New Zealand to exploit already established markets for razor clams through development of fisheries or aquaculture industries for the New Zealand razor clam, Zenatia acinaces. However, fishery or aquaculture development for Z. acinaces requires an understanding of the reproductive cycle including the timing of gametogenic development and spawning. The reproductive cycle of Z. acinaces was studied over an 11‐month period from May 2000 to March 2001 at Kennedy Bay, Coromandel Peninsula, using qualitative standard histological analysis and quantitative measures of oocytes. Histological analysis indicated that Z. acinaces is dioecious and gametogenic development was synchronous between the sexes. Gametogenesis began in June with gametes maturing quickly and by August/September (late winter/ early spring) most razor clams were ripe. Spawning began as early as September (spring) although spawning mainly occurred during October. By December (summer), nearly all clams were completely spent. From January 2001 most clams could not be sexed as all residual gametes were resorbed. Razor clams remained in this stage during March 2001. Spawning began when the water temperature was around its lowest, c. 15°C. Monthly mean number of eggs/follicle was sensitive to changes in reproductive development, closely following patterns observed in the qualitative stagings. Patterns of monthly mean oocyte diameters did not adequately describe the spawning events observed in qualitative analyses. Sex ratios were equal over the size range (69–99 mm shell length) of clams that could be sexed. The data presented in this study provide valuable information on the timing of spawning events for Z. acinaces, necessary for developing sustainable management strategies and selecting broodstock for aquaculture.     

Migratory behaviour of spawning rainbow trout (Oncorhynchus mykiss) in the Tongariro River,New Zealand,after habitat alteration

The movements of 92 adult rainbow trout (Oncorhynchus mykiss) from Lake Taupo into the Tongariro River, New Zealand, were monitored using radio‐telemetry every 3 days during the main spawning period between May and November 2003. This study repeated one previously conducted in 1995. Differences in spawning site preference and resting locations between 1995 and 2003 probably reflect differences in the nature of the river as a result of major natural floods that occurred in 1998. Average migration times were slower than in 1995 and the correlation between flow and mean daily movement was less distinct owing to the dry and settled weather during July and August, although fish did respond to freshets when they occurred. Peak movement occurred between 1600 and 2000 h NZ Standard Time with no movement occurring between midnight and 0400. Fish adjusted their movement in response to changing photoperiod. Nineteen fish were observed above the mouths of natal tributary streams for several weeks in the main river stem before entering these tributaries.     

Characterization of hydraulic suitability of Chinese sturgeon (Acipenser sinensis) spawning habitat in the Yangtze River

Hydrodynamic flow fields affect the ecological processes such as the water diversity and the distribution of organisms. Understanding the hydrodynamic and ecological processes is critical for the restoration and protection of especially fragile ecological habitats in river systems. This study uses turbulent flow to characterize the ecological behaviour of Chinese Sturgeon (Acipenser sinensis) in the Yangtze River. The Delft3D‐Flow model, which is first validated with field‐measured data, is used to simulate the flow field within spawning habitats of Chinese Sturgeon, downstream of Gezhouba Dam. The model‐simulated turbulent kinetic energy (TKE) and its distribution pattern are then used to characterize the hydraulic environment of the fish's spawning habitat. For the spawning habitat, downstream of Gezhouba Dam, the lower limit of TKE for the Chinese Sturgeon egg mass field is 0.025 m²/s², which occurs at a velocity less than 1.7 m/s. Chinese Sturgeon prefers habitats with TKE range of 0.010 ~ 0.015 m²/s² for resting. This suggests that discharge regimes provide the basis for ecological regulation of the Three Gorges Reservoir and the scientific reference for river management. Copyright © 2011 John Wiley & Sons, Ltd.     

Groupers on the Edge: Shelf Edge Spawning Habitat in and Around Marine Reserves of the Northeastern Gulf of Mexico

The northeastern Gulf of Mexico contains some of the most diverse and productive marine habitat in the United States. Much of this habitat, located on the shelf edge in depths of 50 to 120 m, supports spawning for many economically important species, including groupers. Here, we couple acoustic surveys with georeferenced videography to describe the primary spatial and geologic features of spawning aggregation sites for four economically important species: gag (Mycteroperca microlepis), scamp (M. phenax), red grouper (Epinephelus morio), and red snapper (Lutjanus campechanus), with notes on fish distribution and abundance and spawning activities. We provide information on movement patterns of reef fish determined using acoustic telemetry. Finally, we discuss the possible coupling of geomorphology with hydrographic features to influence the overall productivity of the region and the importance of spatial fishery management in sustaining that productivity.     

厦门文昌鱼人工繁殖和幼虫发育及其变态的研究

用组织学和胚胎学方法对厦门国家级自然保护区文昌鱼的生殖季节、胚胎发育和幼虫培育进行详细研究,结果表明,自然保护区文昌鱼生殖季节可分为两个繁殖时期,从6月初开始至7月初为繁殖高峰期,8和9月为繁殖小产期.观察人工繁殖得出,文昌鱼(Branchiostoma belcheri)产卵时间在傍晚19:00前后,可以观察到雌、雄文昌鱼的产卵和排精行为:雄性文昌鱼先离开沙,并跃出水面快速游动和排精,接着雌鱼也跃出水面,所有的卵通过破裂的性腺壁进入到围鳃腔并通过围鳃孔到水中受精,受精率在98.5%以上,还观察了文昌鱼幼虫发育并变态为幼鱼(长度为1.05～13.5mm)的全过程.     

日本鬼鱼由工厂化育苗技术研究

从北部湾沿海采捕的日本鬼鱼由 ( Inimicus japonicus)亲鱼 ,经暂养后进行催产 ,雌鱼每千克体重注射 L RH-A3 1 0μg DOM 5mg或 HCG 60 0～ 80 0 IU LRH-A3 3 0～ 4 0μg;雄鱼注射同样药物 ,剂量减半。共采卵 1 0 9万粒 ,平均受精率 89.0 % ,平均孵化率 90 .0 % ,共培育出体长 1 .8～ 2 .3 cm的幼鱼 2 6.8万尾 ,平均成活率 3 0 .7%。     

普里兹湾邻近海域大磷虾的生殖特点研究

本文依据 1 989/1 990和 1 990 /1 991夏季 ,“极地”号考察船在普里兹湾邻近海域 (南大洋的印度洋区 )的拖网样品 ,对大磷虾的性腺发育和生殖群体的年龄结构等 ,进行了分析研究。大磷虾的生殖开始于 1月 ,一直持续到 3月。高峰期出现在 2月中旬 ,比大西洋区相比迟了一个月。生殖群体主要包括两个年龄组 ,即 3 + 龄和 4+ 龄。换句话说 ,绝大部分个体是三年性成熟 ,一生可生殖两次 ,不排除少数个体两年性成熟 ,或第三次性成熟的可能 ,但比例非常小。在 5 91 6尾能区分性别的个体中 ,雄性个体只占 3 4 .1 %。雄性比随体长的增加而降低。体长大于 5 0 mm的个体中雄性仅占 2 2 .9%。