Coping with aquatic hypoxia: how the plainfin midshipman (Porichthys notatus) tolerates the intertidal zone
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Although plainfin midshipman (Porichthys notatus) are primarily known for their alternative reproductive tactics, and the dimorphic male subtypes, in which Type-I males demonstrate parental investment and mate attraction, and Type-II males ‘sneak’ fertilization and show no investment after fertilization, little is known about the physiology and tolerance to low aquatic oxygen while nesting in the intertidal zone. In May 2007, females and Type-I and Type-II males were collected, and in June 2009, only Type-I males were collected from nest sites on the coast of Vancouver Island, British Columbia. In the 2007 season, an initial assessment of hypoxia tolerance and nest parameters was recorded for the three subtypes of midshipman. Historical evidence indicates that Type-I males remain on the nest for prolonged periods, and our results suggest they can cope with repeated bouts of aquatic hypoxia by elevating their hematocrit and tolerating high lactate levels. The 2009 season was directed at examining the aquatic hypoxia tolerance of only the Type-I male. Hypoxic (~15 % air saturated water) Type-I males had oxygen consumption rates at ~12 % of the normoxic control (~100 % air saturated water) and a Pcrit, the critical oxygen tension, when a fish switches from oxyregulator to oxyconformer, could not be determined; an indication that these fish are solely oxyconformers. With prolonged exposure to aquatic hypoxia, Type-I males displayed significant elevations in plasma and tissue lactate (heart), tissue glucose (liver), and a depression in gill Na+/K+ATPase and catalase activities. Results suggest that male Type-I midshipman survival in the intertidal zone is enhanced by metabolic depression and tolerance to anaerobic byproducts.
KeywordsAquatic hypoxia Plainfin midshipman Marine Intertidal
The authors wish to thank the staff at the Bamfield Marine Sciences Centre (BMSC) for their help and cooperation during this study. We are particularly indebted to the research coordinator Bruce Cameron for his helpful assistance. Additional thanks are extended to Carol Bucking, Karlee Craig, Risa Smith, Sue Walsh, and Tom Mommsen for the assistance in field collection of midshipman. This work was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants to CMW and PJW, an NSERC Discovery Grant and an Ontario Ministry of Innovation Early Research Award to GBM, and a Canadian Society of Zoologists Student Travel Research Grant to JLF. Both JLF and PMC were recipients of NSERC postgraduate scholarships. CMW and P JW are supported by the Canada Research Chair Program. This research was approved by the Animal Care Committee at BMSC and animals were collected under permits from the Department of Fisheries and Oceans Canada.
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