Reproductive biology of Diopatra neapolitana (Annelida,Onuphidae), an exploited natural resource in Ria de Aveiro (Northwestern Portugal)

Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species.     

Reproductive biology of the mackerel scad Decapterus macarellus from Cabo Verde and the implications for its fishery management

The mackerel scad Decapterus macarellus is of great social and economic importance to Cabo Verde citizens; however, in recent years catches have shown an unexplained decline. The harvest is regulated by way of a minimum legal size and a seasonal closure, with both measures based on the results of reproductive studies that did not consider the microscopic characteristics of the gonads. This study aimed to analyse the gonads microscopically in order to classify the sexual development stage of individuals and to estimate the size at first maturity and the reproductive season. This information was then used to analyse the match between the reproductive parameters and the management measures. The samples comprised 284 females (20–36 cm fork length [FL]) and 85 males (21–35 cm FL). The annual variation in gonadosomatic index and the monthly frequencies of mature phases suggest that the reproductive season occurs from March to October, with two spawning peaks, one in March and another from July to October. The current seasonal closure (from July to September) covers the main reproductive period. However, the species has a long spawning period and the timing of peaks can vary between years; hence, a reassessment of this management measure is recommended. The sizes at first maturity were estimated at 24.1 cm FL for females, and 26.6 cm FL for males. These values are higher than the minimum legal size (20 cm FL) currently established for management of the species at Cabo Verde; thus, we strongly recommend an increase in the minimum legal size in an attempt to reduce catches of immature individuals.     

Age,growth and natural mortality of blue jack mackerel Trachurus picturatus (Carangidae) from the Canary Islands,Spain (NW Africa)

Status assessment of exploited fish populations is a general requirement to ensure sustainability of fisheries in both global and local contexts. The blue jack mackerel Trachurus picturatus (Bowdich, 1825) remains unassessed in a data-limited fishery in the eastern central Atlantic, within the waters of the Canary Islands (Spain) off the coast of northwest Africa. This is the most southwestern targeted fishery in the species’ distributional range. To obtain basic life-history information, a total of 2 472 specimens were analysed, ranging from 10.2 to 31.9 cm total length, from samples collected monthly between March 2005 and March 2006. Length–weight relationships (a = 0.0023; b = 3.418; R ² = 0.97) showed no significant difference between sexes. Deposition periodicity and coherence of the ageing criteria were verified by analysis of the monthly evolution of the otolith edge. Ages were estimated by counting annual growth rings on whole otoliths, with these fish ranging from age 0 to 6 years. The von Bertalanffy growth model, which was used to estimate growth parameters from both direct readings and back-calculated length-at-age data, gave good statistical fits. The parameters from the direct readings were: L∞ = 34.9 cm; k = 0.214 y^–1; t ₀ = ?2.545 y (R ² = 0.84), and the natural mortality rates estimated from empirical methods varied between 0.20 and 0.55 y^–1.     

Aspects of the biology of the sandsmelt Atherina boyeri Risso, 1810 (Teleostei: Atherinidae) at Oldbury-upon-Severn,Gloucestershire, England

The age structure, annual growth, length-weight relationship, reproduction and other aspects of the general biology in Boyer's sandsmelt, Atherina boyeri, from the Severn estuary, have been studied for the period 1974–1977. The results are compared with those found in previous investigations of A. boyeri from more southerly waters.     

Reproductive biology of the leatherjacket,Meuschenia scaber (Monacanthidae) (Forster 1801) in the Hauraki Gulf,New Zealand

The leatherjacket Meuschenia scaber is widely distributed in Australasian waters, and is a valued bycatch of inshore bottom trawl fisheries although little is known of its life history. Here, we describe the reproductive biology of the species based on 651 leatherjackets sampled in the Hauraki Gulf, New Zealand, between July 2014 and March 2016. The maximum total length (L_T) recorded for females and males were 320 and 315?mm, respectively, with both sexes present in all size classes. Monthly analysis of gonad condition revealed a clear spawning season from late austral winter to early summer (August–December), and histological analysis of the ovaries revealed that M. scaber is an indeterminate serial spawning gonochorist. The estimated sizes at sexual maturity (L₅₀) for females (189.9?mm L_T) and males (188.4?mm L_T) did not differ significantly. Relatively small testes, sexual dimorphism and underwater observation of nesting suggest that M. scaber is a paired spawner.     

廉州湾红树蚬的繁殖生物学研究

2011年8月至2012年7月,采集广西北海廉州湾红树蚬(Polymesoda erosa)的周年样品进行了性腺发育、生殖周期和胚胎发育研究。结果表明,红树蚬雌雄异体,性别可通过成熟生殖腺颜色区分;1年1个生殖周期,性腺发育可分为增殖期、生长期、成熟期、排放期和休止期5个阶段,性腺发育两性同步;繁殖期从6月延续到11月,其中7月和10月为繁殖高峰期;肥满度指数最高为5.19%(5月份),最低为1.98%(2月份);繁殖方式为非孵育型,沉性卵,外被一层厚的胶质卵膜,水温26℃时,D形幼虫孵出时间约为27h。