Abstract
Blooms of the planktonic alga Prymnesium parvum pose a global threat, causing fish kills worldwide. Early studies on the exposure of fish to P. parvum indicate that toxic effects are related to gill damage. The more strictly defined concept of adverse outcome pathways has been suggested as a replacement for the mode of action in toxicology studies. In this study, rainbow trout (Onchorhyncus mykiss) were exposed to P. parvum. During exposure, oxygen consumption was determined by respirometry, and ventilation and coughing rate were determined via video surveillance. Per breath oxygen consumption was calculated to assess the ventilation effort to obtain a unit of oxygen. A second experiment monitored fish behavior to assess recovery. The results indicated that oxygen consumption initially increased, but on average fell below the standard oxygen consumption at 70% relative exposure. Being a function of ventilation frequency and oxygen consumption, the per breath oxygen consumption decreased throughout exposure. Behavioral results determined that short-term P. parvum exposure subsequently caused the exposed fish to seek flow refuge immediately and to a greater extent than unexposed fish. The adverse outcome pathway of P. parvum on rainbow trout is that P. parvum acts as a gill irritant resulting in non-recoverable respiratory failure.
Highlights
Harmful algal blooms (HABs) caused by a variety of planktonic algae are associated with fish kills in nature [1,2,3]
The standard metabolic rate determined in this study (81.17 ± 15.7 mgO2 kg−1∙h−1; the baseline pre‐exposure level of MO2) was slightly higher than previously reported values using intermittent flow respirometry for a rainbow trout of the same size (150 g) and the same temperature of 10 °C
The standard metabolic rate determined in this study (81.17 ± 15.7 mgO2 kg−1· h−1 ; the baseline pre-exposure level of MO2 ) was slightly higher than previously reported values using intermittent flow respirometry for a rainbow trout of the same size (150 g) and the same temperature of 10 ◦ C
Summary
Harmful algal blooms (HABs) caused by a variety of planktonic algae are associated with fish kills in nature [1,2,3]. The existing knowledge on the mechanistic effects of P. parvum exposure indicates that an increase in gill permeability is causing sensitivity to subsequent secondary toxicity as the primary mode of action [6,7,8], but other mechanisms of action, such as hemolysis and anti-coagulant properties, have been proposed [13,14,15,16,17]. None of these hypotheses have been confirmed by a physiological study of P. parvum on the whole fish. During the pre-exposure period, the coughing frequency was very low, and if 10 events did not occur within 120 s, the frequency was set to zero
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