Increased concentrations of CO2 in the atmosphere will cause not only global warming but also raised partial pressure of CO2 and lowered pH in the ocean. These environment alterations may affect fish and other marine organisms. On the other hand, feasibility studies recently suggest that disposal of anthro-pogenic CO2 in the deep ocean could help reduce atmospheric CO2 concentrations. However, implementation of this strategy could have a significant environmental impact on marine life. These circumstances provide a background for the urgent need of further studies concerning the effect of CO2 on fish. In this paper we sum-marize the literature reporting on CO2 effects on fish and discuss the required research work for the future.
The present knowledge from the literature is summarized and categorized into oxygen consumption rate, respiration activity, oxygen carrying capacity by red blood cells, blood gas, blood circulation, CO2 receptor, acid-base balance, endocrine, growth, toxicity and anesthesia. Most of the experimental fish used in the literature are freshwater species (carp and rainbow trout have largely been used). There were only few examined marine species (three bottom dwelling species of elasmobranch and teleost, respectively). Since experiments have only been carried out on adult fish, experiments on reproduction and the early life stage should be performed to clarify effects over the life cycle and to predict long term hypercap-nic effects. Physiological studies have mostly been concerned with the acid-base balance and we need further information on maturation and endocrine to evaluate long term hypercapnic effects on fish populations. Changes in swimming behavior and its mechanism must also be examined.
Although the early phase of future study on CO2 effects on fish has to start using shallow-water species, deep-sea species should be considered in concern with the disposal of CO2 in the deep ocean. Furthermore, extrapolating data from one well researched species to evaluate implications on the ecosystem as a whole would be hazardous. In order to validate an appropriate resolution to the global warming problem, a multi-disciplinary approach to the effects of CO2 disposal utilizing spe-cialists from fields such as marine biology, fisheries and physical oceanography is clearly necessary.
