Scientists at the University of British Columbia have modeled the impact rising temperatures could have on more than 600 species by 2050.
Decreasing oxygen levels caused by warmer waters could reduce fish body weight as well as have an effect on the distribution and the reproductive abilities of many species, the researchers said.
Relatively small changes in temperatures could have "unexpectedly large" impacts on fish body size, they said, because the level of oxygen in the water is affected.
"Rising temperatures directly increase the metabolic rate of the fish's body function," study lead author William Cheung told BBC News.
"This leads to an increase in oxygen demand for normal body activities. So the fish will run out of oxygen for growth at a smaller body size."
Fish body size could shrink between 14 percent and 24 percent, the researchers said, with the largest decreases in the Indian and Atlantic oceans.
The study was published in the journal Nature Climate Change.