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11 pages, 5 figures, 2 tables.-- PMID: 18665231 [PubMed].-- Supporting information available: Supplementary Table "Field and laboratory data used for the assessment of the presence of temperature-dependent sex determination in gonochoristic fish" and list of references ; [Background] In gonochoristic vertebrates, sex determination mechanisms can be classified as genotypic (GSD) or temperature-dependent (TSD). Some cases of TSD in fish have been questioned, but the prevalent view is that TSD is very common in this group of animals, with three different response patterns to temperature. ; [Methodology/Principal Findings] We analyzed field and laboratory data for the 59 fish species where TSD has been explicitly or implicitly claimed so far. For each species, we compiled data on the presence or absence of sex chromosomes and determined if the sex ratio response was obtained within temperatures that the species experiences in the wild. If so, we studied whether this response was statistically significant. We found evidence that many cases of observed sex ratio shifts in response to temperature reveal thermal alterations of an otherwise predominately GSD mechanism rather than the presence of TSD. We also show that in those fish species that actually have TSD, sex ratio response to increasing temperatures invariably results in highly male-biased sex ratios, and that even small changes of just 1–2°C can significantly alter the sex ratio from 1:1 (males:females) up to 3:1 in both freshwater and marine species. ; [Conclusions/Significance] We demonstrate that TSD in fish is far less widespread than currently believed, suggesting that TSD is clearly the exception in fish sex determination. Further, species with TSD exhibit only one general sex ratio response pattern to temperature. However, the viability of some fish populations with TSD can be compromised through alterations in their sex ratios as a response to temperature fluctuations of the magnitude predicted by climate change ; Work supported by a Spanish Ministry of Education and Science grant ("Sexratio") to F.P. N.O.A. was supported by a scholarship from the aquaculture network (XRAq) from the Government of Catalonia ; Peer reviewed

10 páginas, 6 figuras, 1 tabla ; The coastal lagoon of Bahía-Magdalena, located on the west coast of the Peninsula of Baja-California, is a subtropical ecosystem with an arid climate and very little freshwater input. During the 2005–2011 period the thermohaline properties varied between cold and warm half-yearly periods. They were influenced by the Transitional Water mass transported by the South California Current from February to July and by the Subtropical Surface Water from August to January. The nutrient concentrations increased (viz up to 16 μM of nitrate) from March to June, when the upwelling index was the highest. Similarly, the inter-annual variation of chlorophyll-a showed a six-monthly pattern with the highest average monthly concentrations being found in June (5 mg m−3in situ or 8 mg m−3 based on satellite information) and the lowest in December–January. A spatial zoning was also observed in the lagoon with a shallow inner zone that is warmer and richer in chlorophyll-a than the deeper closed mouth area. In the Bahía-Magdalena lagoon a spatial-temporal division into two zones and two seasons was repeated year after year with only minor differences. During the first semester in the outer zone, years 2006 and 2007 were colder and nutrient rich while 2010 was warmer, according to the upwelling conditions in the Southern California Region. Hence, among the coastal lagoons that present a prevailing marine influence, the coastal system of Bahía-Magdalena corresponds to an unusual type of subtropical coastal lagoon where the nutrient input is mainly due to upwelling phenomena. ; his article was supported by the SIP Mexican projects of the Instituto Politécnico Nacional from 2005 to 2011 in cooperation with the Spanish project CTM2011-28792-C02 financed by the 'Ministerio de Economía y Competitividad'. We are very grateful to the Mexican COFAA (IPN) organism and EDI program for their grants and to the Mexican governmental agency CONACYT for financing the sabbatical (ref. 169030) of Dr. Rafael Cervantes-Duarte at the IIM (CSIC) of Spain during 2012. ; Peer reviewed