large fish slowly and happily swims through a pool close to the camera

large fish slowly swims close camera aquatic habitat freshwater stream rivers scales carnivorous omnivorous invertebrates crustaceans zooplankton phytoplankton forage breeding behavior symbiosis decomposition filtration oxygenation photosynthesis nutrients dissolved oxygen temperature salinity pressure migration reproductive cycle spawning eggs schooling shoaling predatory camouflage life forms plants algae benthic body territorial communication bioluminescence