Thesis Title

The Effects of Glochidiosis on Fish Respiration

Date of Graduation

Fall 2005

Degree

Master of Science in Biology

Department

Biology

Committee Chair

M. Chris Barnhart

Keywords

Unionid mussels, hypoxia, glochidiosis, fish respiration, parasitism

Subject Categories

Biology

Abstract

Freshwater mussels of the family Unionidae begin life as parasitic larvae, known as glochidia. These larvae are temporary parasites on the gills or skin of fish. Little is known of the pathological effects of glochidia on their hosts (glochidiosis). Thus, the existence of an evolutionary arms race between mussels and their hosts is problematic. I investigated the effects of glochidia of Mapsilis reeveiana, broken ray mussel, on respiration of Micropterus salmoides, largemouth bass. I predicted that glochidiosis would impair gas exchange because the formation of glochidial cysts on the gills increases the diameter of the gill filaments and obliterates the Lamellae in the affected area, increasing diffusion distance while reducing the surface area for gas exchange. Fingerling bass (̃5 g) were infected with 0-1006 glochidia per fish. In normoxic water, resting ventilation rates were elevated in proportion to the number of attached glochidia and up to 2X controls. The rate of oxygen consumption (MO2) and tolerance for hypoxia (critical DO at which ventilation ceased) were tested in closed chambers. MO2 decreased as the infection rate increased in near-normoxia. Critical DO was elevated up to 2X by glochidiosis. The largest effects occurred during the period of excystment of juveniles from the fish. Thereafter effects decreased but were still significant 2.5 months after excystment. Microscopic examination at that time showed shortened or missing gill filaments and lamellae. The results indicate that glochidious can cause significant and persistent impairment of gill function. Hosts might also be exposed to increased predation if compensatory hyperventilation attracts the attention of predators. Selection pressure on fish to avoid glochidiosis presumably results in reciprocal selection on mussels to evolve ever more sophisticated lures.

Copyright

© Brianna E. Kaiser

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