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Intertidal spawning of chum salmon : saltwater tolerance of the early life stages to actual and simulated intertidal conditions

University of British Columbia

Intertidal spawning of chum salmon, Oncorhynchus keta. was investigated by measuring egg survival, development, and saltwater tolerance under actual and simulated intertidal conditions. Intragravel salinity and temperature were monitored in the intertidal zone of Carnation Creek, British Columbia, using salinity and temperature probes implanted in the gravel at five locations, ranging from the 1.9- to 2.9-meter tide level. Artificially implanted eggs, placed adjacent to these probes, were monitored to determine the effect of observed intertidal conditions on egg survival and development. Intragravel oxygen and gravel quality also were measured at these stations. Saltwater inundation of the gravel streambed resulted in intragravel salinities as high as 30‰ for durations up to 8 h, twice daily. Due to regular inundation of warmer saltwater, egg development at the lower intertidal sites was more rapid than the upstream freshwater control sites. Survival in the intertidal zone ranged, from (0-51.2%). In general, no negative effects of saltwater exposure on egg survival were observed. Instead, egg survival was strongly correlated with intragravel oxygen. It is suggested that eggs in the intertidal zone may benefit from the interchange of intragravel water and the subsequent added availability of oxygen, resulting from regular inundation of seawater into the streambed. Laboratory experiments were designed to test saltwater tolerance of eggs under simulated intertidal conditions. When eggs were transferred to or from saltwater, measurement of perivitelline fluid osmolality changes showed thatequilibration with the ambient medium occurred rapidly (15-25 min). This response was modelled and an equation was determined. Eggs were exposed daily to two intermittent exposure regimes (4 and 8 h) and one constant one (24 h), at six different salinities (0, 5, 10, 15, 20, and 30‰). Survival was measured from fertilization to 8 d post-hatching. No eggs survived in any of the 30‰ salinity treatments. In the intermittent exposure treatments (4 and 8 h) eggs tolerated salinities of 15‰ or less with no adverse effects. Eggs exposed to 20‰ for 4 h also showed no adverse effects, whereas those in the 8 h exposure suffered about 55% mortality. In the constant exposure treatments only eggs in 5‰salinity and the control survived to the alevin stage (85-95%). In general, eggs in the higher salinities hatched first, although no obvious developmental differences were noted between survivors from the different treatments. Possible mechanisms of saltwater toxicity are discussed and it is suggested that eggs provided with a short period of freshwater exposure between saltwater exposures are much more tolerant than eggs exposed to saltwater continuously. Effects of ambient saltwater on the fertilization process were examined by testing sperm motility, sperm viability and combined sperm and egg viability in various salinities (0, 5, 10, .12.5 and 15‰). In the sperm motility tests no differences were noted between individual males. However, more vigorous activity and longer periods of motility were observed in salinities ranging from 5-10‰ than salinities of 0 and 12.5‰. No measurable motility was observed in 15‰- Sperm viability, measured as fertilization success (FS), indicated that sperm were more viable in 12.5 and 15‰ than was suggested by the motility measurements. High FS (90-95%) occurred in salinities ranging from 0-10‰ whereas significantly lower FS occurred in 12.5 and 15‰. Combined egg and sperm viability, also measured as FS, showed a similar response as the sperm viability test. However, a lower FS in 15‰ in the combined test suggested that saltwater had an added effect on the egg, in addition to its inhibitory effect on the sperm. It is concluded that eggs deposited by intertidal spawning salmon during times of saltwater inundation would have low to nil FS.

Text

2010-08-16

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http://hdl.handle.net/2429/27468

Zoology

University of British Columbia

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