Save the … parasites? Analyzing 140 years of parasite abundance in fish shows dramatic declines, especially in parasites that rely on three or more host species. The decline is linked to warming ocean temperatures. Parasitic species might be in real danger, researchers warn — and that means not just fewer worms, but losses for the entire ecosystem.Save the … parasites? Analyzing 140 years of parasite abundance in fish shows dramatic declines, especially in parasites that rely on three or more host species. The decline is linked to warming ocean temperatures. Parasitic species might be in real danger, researchers warn — and that means not just fewer worms, but losses for the entire ecosystem.