Stable isotopes in fish otoliths discriminate between lagoonal and oceanic residents of Taiaro Atoll (Tuamotu Archipelago, French Polynesia)

 The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures, suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work to determine which individuals and species complete their life-cycles in this unusual lagoon. Accepted: 28 August 1997     

The Lusitanian toadfish as bioindicator of estuarine sediment metal burden: The influence of gender and reproductive metabolism

Early diagenetic processes and anthropogenic activities are responsible for metal enrichment in estuarine sediments. The Tagus estuary (Portugal) is no exception, and as a result of past and present pressures, surface sediment contamination is still an issue in some areas. Since such metal loads may be incorporated by benthic organisms, this study analyzed the accumulation of trace metals in the Lusitanian toadfish (Halobatrachus didactylus) in the Tagus estuary. In order to determine the role played by the seasonal reproductive cycle of the Lusitanian toadfish in the bioaccumulation process of trace metals in its tissues, the concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn were determined in the liver of male and female specimens captured during reproductive and non-reproductive periods. The results showed that metal accumulation in the liver was related simultaneously with gender and season, with females having higher levels of Cd, Cu and Zn during the reproductive period. The metabolic roles of Cu and Zn in embryonic development may explain such results, as both metals accumulated in the female liver to be transported to the gonads later on. Cd, on the other hand, does not have a metabolic role, and the higher concentrations of this metal found in spawning females could be related to the high affinity of Cd to vitellogenin, which is produced in the liver. To assess the species’ potential as an indicator of metal contamination, the concentrations of the seven elements were compared in the muscle tissue of adult, type I males (age ≥5), from two areas with distinct sediment metal loads. Non-essential metals in the muscle reflected the same differences between areas that were found in the sediment samples, evidencing H. didactylus as a potential indicator of those elements bioavailability from the sediment. The results showed that the muscle tissue of adult specimens of a relatively sedentary species such as H. didactylus is a useful indicator of long term accumulation of trace metals. On the contrary, liver concentrations of trace metals showed variation according to the reproductive status, which could lead to overestimate of the environmental status concerning trace metals bioavailability. Spawning season and liver tissue should thus be avoided in biomonitoring studies targeting this benthic fish.     

Reproductive behavior and social organization in the sand tilefish,Malacanthus plumieri

Synopsis Observations on the Caribbean sand tilefish, Malacanthus plumieri, were made during 3 dive trips in the Bahamas (Feb., 1986; July, 1986; Jan., 1987) at depths from 5 to 30 m. Eighteen mating groups contained 1 to 5 females (x = 2.9). Seven male home ranges (encompassing female ranges within mating groups) measured 250 to 700 m². Of 134 paired rises recorded between 1733 and 1925 h EST, 38 had an observed cloud of gametes. Mating times are presented in relation to time of sunset and depth of water. Courtship begins with conspicuous looping behavior of the male as he swims to a female. Close pairing, criss-crossing, and low rises (<1.5 m) often precede a high quivering upward swim (1.5 to 6 m) which culminates in the release of a cloud of gametes at the apex. M. plumieri is compared to the protogynous hermaphroditic razorfishes, Xyrichtys pentadactylus and X. martinicensis, with regard to social organization, size of male home ranges in exposed sandy habitats near coral reefs, sexual size dimorphism, and sex ratio.     

Duplication and distinct expression patterns of two thrombospondin-1 isoforms in teleost fishes

Two types of thrombospondin-1 (named TSP-1a and TSP-1b) were cloned from two species of teleosts, the Nile tilapia and medaka. Phylogenetic analysis of these TSP-1 sequences, together with those available from other vertebrates further demonstrated that two types of TSP-1 exist only in teleosts, extending the finding in fugu and tetraodon to two additional fish species. The expression of both genes was examined using tilapia at various developmental stages. Tilapia TSP-1a and TSP-1b were each expressed in a wide range of tissues examined. The early expression of TSP-1b in both XX and XY gonads from 5 dah (day after hatching) onwards suggested an important role in the formation of gonads, while the expression of TSP-1a only in ovaries during later stages of development (from 120 dah onwards) may suggest that TSP-1a is involved in oogenesis. During the 14-day spawning cycle, the expression of both types of TSP-1 exhibited distinct peaks at day 5 (peak of vitellogenesis) and day 12 (oocyte maturation). In situ hybridization analyses revealed differential expression, with TSP-1a occurring in granulosa cells and TSP-1b in theca cells. Furthermore, both TSP-1a and -1b were expressed in skeletal tissues but with clear temporal and spatial differences. In contrast, only TSP-1b was found in the myosepta. The positive signals of both TSP-1a and TSP-1b were also detected in the heart and spleen, and TSP-1a in brain and intestine by both RT-PCR and in situ hybridization.     

大口黑鲈的卵巢发育周年变化及反季节繁殖研究

文章研究了华中地区池塘养殖大口黑鲈(Micropterus salmoides)卵巢的发育规律, 分析了水温与光照条件变化对卵巢发育的影响, 探究了大口黑鲈反季节繁殖的方法, 旨在充分利用本地区的气候条件, 化劣势为优势, 从根本上解决本地大口黑鲈产业所面临的问题。实验采用形态学、组织学等方法比较分析了大口黑鲈卵巢发育特征, 采用人工控温和人工促熟的方法探究了温度和性激素对大口黑鲈性腺启动发育的影响。研究发现, 华中地区大口黑鲈雌鱼性腺指数(GSI)周年变化在0.63%—7.95%, 10月中旬至12月初水温由20.6℃降至11.0℃期间, 卵巢开始发育至Ⅲ期, 并以Ⅲ期越冬, 至4月中旬繁殖产卵, 5月底结束, 繁殖前约80%的雌鱼绝对繁殖力在4.5万—6.5万粒, 但受水温升高的影响, 卵巢中15%成熟卵母细胞未能产出而逐步退化, 产卵结束时仍有一半以上卵未产出(GSI为4.6%); 雌鱼GSI与肠系膜脂肪系数(MFI)、肝体比(HSI)在10月份至次年4月份呈显著负相关(P<0.05), 表明在此期间, 机体储存的营养物质部分转移至性腺, 优先保证性腺发育。在大口黑鲈反季节繁殖实验中, 采用井水[水温(20±1)℃]降温和控温处理的方法能够促进大口黑鲈性腺的启动发育, 经过3个月处理, 控温组雌鱼卵巢发育至Ⅳ期末, GSI达到4.06%, 而对照组雌鱼卵巢处于Ⅲ期, GSI为2.52%, 两组差异显著(P<0.05), 两组雄鱼精巢均发育至Ⅳ期末, 控温组GSI达0.89%, 对照组为0.73%, 这表明可以通过温度处理来调控大口黑鲈性腺的发育。最后针对反季节繁殖中亲本的培育方法和处理时间等进行了总结, 以期为后续培育反季节大口黑鲈提供依据。     

Reproductive biology of the endemic Iranian cichlid, <Emphasis Type="Italic">Iranocichla hormuzensis</Emphasis> Coad, 1982 from Mehran River,southern Iran

We studied the reproductive biology of the endemic Iranian cichlid Iranocichla hormuzensis, a maternal mouthbrooder, in the Mehran River. Overall sex ratio was 1.44 M: 1F indicating a significant male bias. Monthly sex ratios did not differ from unity except in May and June when the sex ratios were strongly biased in favor of males. Four different reproductive indices and the high frequency of large oocytes, all suggest that the Iranian cichlid spawns at the end of winter and the beginning of spring. Mircoscopic gonadal maturation stages for both males and females were correlated to the gonadosomatic indices. The maximum number of larvae in the mouth of a female was 153.     

Breeding strategy of Acrossocheilus fasciatus in the Puxi Stream of the Huangshan Mountain

Breeding strategies of Acrossocheilus fasciatus were studied from 592 specimens collected monthly during May 2007 and April 2008 in the Puxi Stream of the Huangshan Mountain.Sex ratio of the studied population was 0.90∶1(♀∶♂),not significantly different from 1∶1.Both sexes reached their first sexual maturity at age 2(the second calendar year of their birth).Fifty percent of females and males reached maturity at a total length of 69.75 mm and 69.36 mm respectively,and the minimum total length was 61.54 mm an...     

Lake water level increase during spring affects the breeding success of bream Abramis brama (L.)

In Lake Constance, Eurasian bream Abramis brama (L.) spawn in very shallow littoral areas by the beginning of May. They attach their adhesive eggs to pebble and cobble substratum at <40 cm depth. Increasing water levels before spawning inundate bare substratum to which bream eggs may attach better than to deeper substratum covered by epilithon. Consequently, the water level increase prior to spawning should determine the amount of pristine spawning substratum available to bream and thus influence their breeding success. In order to test this hypothesis, the influence of hydrology and climate on the abundance of age-0 bream was combined with the results from field investigations on the egg survival and abundance of age-0 bream. A strong positive correlation between the mean water level increase during the spawning season of bream (April–May) and the abundance of juvenile bream was found. In contrast, the absolute water level during spawning and during the nursery stage in summer, the cumulative temperature during the egg, larval and juvenile stages and two North Atlantic Oscillation (NAO) indices did not affect the abundance of juvenile bream. The field investigations confirmed that bream eggs attach better to and have higher survival rates on bare substratum than on substratum with epilithon cover. Accordingly, eggs within a spawning habitat of bream were most abundant between 10 and 20 cm depth, where the epilithon cover was lower than at depths exceeding 30 cm. The results of this study confirm an adverse influence of epilithon cover on the attachment and subsequent survival of bream eggs and emphasize the importance of spring inundations for the successful breeding of the bream. Handling editor: J. A. Cambray