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Field and laboratory investigations of Echyridella menziesii (Unionida : Hyriidae) interactions with host fishes / by Nicole Joy Hanrahan.

By: Hanrahan, Nicole Joy [author.].
Contributor(s): University of Waikato [degree granting institution.].
Material type: materialTypeLabelBookPublisher: [Hamilton, New Zealand] : University of Waikato, 2019.Description: 1 online resource : illustrations (chiefly colour), form, maps (chiefly colour).Content type: text | still image Media type: computer Carrier type: online resourceSubject(s): UNIONIDAE | WAIKATO | NEW ZEALAND | THESES | FRESHWATER MUSSELS | GOBIOMORPHUS -- Waikato | PARASITES | FRESHWATER FISH | HOST PARASITE RELATIONSHIPS | PARASITOIDS | NATURAL IMMUNITYHoldings: ELECTRONIC Online resources: University of Waikato Research Commons Dissertation note: Ph. D. University of Waikato 2019 Summary: Globally, the study of freshwater mussels has increased markedly in recent years, spurred on by recognition that many mussel populations are declining or are already extinct. The New Zealand freshwater mussel Echyridella menziesii (Unionida: Hyriidae) has a current threat classification of ‘At Risk, Declining’, in part reflecting disruption of recruitment on host fish. The life cycle of E. menziesii includes a parasitic stage in which the larvae (glochidia) must attach to a host fish to transform into the juvenile stage. However, no research has been conducted to understand whether fish develop immunity that limits infestation rates, and little is known about the spatial and temporal variations of mussel-host interactions in natural environments in New Zealand. This study therefore aimed to: i) determine whether multiple infestations of E. menziesii glochidia influenced the suitability of common bully (Gobiomorphus cotidianus) as a host; and ii) quantify fish host associations over the glochidial release period in three contrasting Waikato streams. Common bully considered naïve to E. menziesii were infested with glochidia in the laboratory, and placed in individual, flow-through tanks (22oC) which were flushed every second day to measure glochidia detachment and juvenile excystment. Fishes were infested either one, two or three times, with ‘control’ fish infested for the first time in the second and third rounds. There were no differences in cumulative detachment rates of glochidia and no major reductions in metamorphosis success across multiple infestations. Metamorphosis success rate across all infestation rounds was ≤30%, and was highest when initial glochidia viability was also high. The lack of detectable immunity in common bully, at least after three sequential infestations, is promising for the future conservation of E. menziesii as host-fish are likely to be repetitively infested with glochidia over the mussel spawning season in a natural setting. Infestation by glochidia was determined on the associated fish community, caught using a combination of electrofishing and minnow trapping. In parallel with these evaluations, mussel brood pouch development was assessed fortnightly from October 2018 to February 2019 at three Waikato stream sites. Peak glochidia release occurred in February when average monthly water temperatures were >18.8oC. A field method was developed to quantify glochidial attachment on external surfaces of fish, while internal attachment (gills, mouth) was quantified by laboratory dissection. While a range of fish hosts were identified, 86% of recorded glochidia were attached to Gobiomorphus species, including redfin bully (G. huttoni) and common/Crans bully (G. cotidianus/G. basalis). Most externally-attached glochidia (73%) occurred on caudal, pelvic and pectoral fins. Host associations appeared to favour benthic rather than pelagic species, and did not change throughout the mussel reproductive season despite seasonal change in fish communities. This research demonstrates that common bully, and more broadly Gobiomorphus species, are important hosts for glochidia and do not develop immunity to repeated infestations. Gobiomorphus species have the potential to be very useful ‘tools’ to assist in restoring E. menziesii populations, and therefore conservation management must consider these host fish populations as well as other habitat and water quality factors affecting E. menziesii.
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A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science (Research) in Ecology and Biodiversity at the University of Waikato.

Supervisors: Kevin J. Collier and Susan Clearwater.

Ph. D. University of Waikato 2019

Includes bibliographical references.

Globally, the study of freshwater mussels has increased markedly in recent years, spurred on by recognition that many mussel populations are declining or are already extinct. The New Zealand freshwater mussel Echyridella menziesii (Unionida: Hyriidae) has a current threat classification of ‘At Risk, Declining’, in part reflecting disruption of recruitment on host fish. The life cycle of E. menziesii includes a parasitic stage in which the larvae (glochidia) must attach to a host fish to transform into the juvenile stage. However, no research has been conducted to understand whether fish develop immunity that limits infestation rates, and little is known about the spatial and temporal variations of mussel-host interactions in natural environments in New Zealand. This study therefore aimed to: i) determine whether multiple infestations of E. menziesii glochidia influenced the suitability of common bully (Gobiomorphus cotidianus) as a host; and ii) quantify fish host associations over the glochidial release period in three contrasting Waikato streams.

Common bully considered naïve to E. menziesii were infested with glochidia in the laboratory, and placed in individual, flow-through tanks (22oC) which were flushed every second day to measure glochidia detachment and juvenile excystment. Fishes were infested either one, two or three times, with ‘control’ fish infested for the first time in the second and third rounds. There were no differences in cumulative detachment rates of glochidia and no major reductions in metamorphosis success across multiple infestations.

Metamorphosis success rate across all infestation rounds was ≤30%, and was highest when initial glochidia viability was also high. The lack of detectable immunity in common bully, at least after three sequential infestations, is promising for the future conservation of E. menziesii as host-fish are likely to be repetitively infested with glochidia over the mussel spawning season in a natural setting.

Infestation by glochidia was determined on the associated fish community, caught using a combination of electrofishing and minnow trapping. In parallel with these evaluations, mussel brood pouch development was assessed fortnightly from October 2018 to February 2019 at three Waikato stream sites. Peak glochidia release occurred in February when average monthly water temperatures were >18.8oC. A field method was developed to quantify glochidial attachment on external surfaces of fish, while internal attachment (gills, mouth) was quantified by laboratory dissection. While a range of fish hosts were identified, 86% of recorded glochidia were attached to Gobiomorphus species, including redfin bully (G. huttoni) and common/Crans bully (G. cotidianus/G. basalis). Most externally-attached glochidia (73%) occurred on caudal, pelvic and pectoral fins. Host associations appeared to favour benthic rather than pelagic species, and did not change throughout the mussel reproductive season despite seasonal change in fish communities.

This research demonstrates that common bully, and more broadly Gobiomorphus species, are important hosts for glochidia and do not develop immunity to repeated infestations. Gobiomorphus species have the potential to be very useful ‘tools’ to assist in restoring E. menziesii populations, and therefore conservation management must consider these host fish populations as well as other habitat and water quality factors affecting E. menziesii.

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