Publication Date

5-1-1996

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Lowered pH conditions in aquatic environments can have a negative impact on many aquatic organisms. In fish it has been shown that acidic water conditions may result in altered gill morphology, reduced reproductive success, changes in locomotor and feeding behavior and even death. Juveniles and adults have been the primary focus of research. However, the larval stage is potentially the most sensitive to toxicity. It is also important ontogenetically as several crucial development thresholds, such as first feeding, occur during this period. The impact of acute low pH on feeding performance was investigated in larval fathead minnows one to fifteen days post-hatching. Each day, replicate sets of five larvae were exposed to each of three pH concentrations (4.5, 5-5, and 7.7) under various environmental conditions: (1) light conditions with live prey (LL), (2) light conditions with dead prey (LD), (3) dark conditions with live prey (DL) and (4) dark conditions with dead prey (DD). Each treatment regime was designed to isolate different sensory modalities available for prey capture. Temporal patterns in locomotor activity were examined qualitativeely using LOWESS and number of larvae feeding across days were analyzed using ANCOVA. Growth rates per day were statistically the same and within normal ranges for each batch of fish. Levels of locomotor activity were uncorrelated with feeding rates and were qualitatively different early vs. late in the larval period when food was present. There was no clear pattern in locomotor activity in the absence of food. pH had a significant negative impact on feeding success, although the nature of this effect varied with respect to test conditions. LD and DD treatments displayed heterogeneity of slopes among pH levels; at pH 4.5, the rate of increase in feeding activity across days was significantly depressed relative to other pH levels. LL and DL treatments were characterized by significant intercept differences among pH conditions; larvae exposed to pH 4.5 showed decreased feeding efficiencies relative to those at higher pH. Mechanoreception appeared to play a significant role in prey capture at pH 7.7, while photoreception contributed little. The removal of any sensory modality seemed to have an impact at pH 5-5, but the degree of impact depended on the sense that was eliminated. pH 4.5 appeared to strongly inhibit chemoreception; the data also suggest close coupling of chemoreception and mechanoreception in feeding. While it is evident that prey capture and feeding success in larval fish is complex, these data show clear impact of pH on feeding performance. These results point to the necessity for studies of acidification effects on larvae and suggest an approach by which aspects of sensory integration may be dissected.

Disciplines

Medical Sciences

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