Longevity
Longevity for most bony fish species is unknown. Large species generally have a longer life expectancy than smaller species, and colder-water species often live longer than warm-water species. Some species live only for a few months. Others, like the orange roughy (Hoplostethus atlanticus) may live for 100 years or longer.
Aging Studies
Growth rings are periodically deposited on the scales, vertebrae, and earstones of many species of bony fishes. Experts can stain these hard body parts, examine them for growth rings, and estimate the age of the fish.
Examining the scales, vertebrae, or earstones of known-age fishes after their death enables researchers to compare the estimated age (based on growth rings) with the fish's known age.
In some species, tagging and releasing fish yields information about growth rates. A tagged fish can be measured again when it is recaptured. Researchers correlate the measurements with the number of years since recapture and estimate a yearly growth rate.
Predation
Depending on the species, bony fishes have a wide variety of predators, including other fishes, birds, reptiles, amphibians, mammals (including humans), and various invertebrates.
Small bony fishes may have a large variety of predators. Large bony fishes have fewer predators.
Fish eggs or larvae may have different predators than adults of the same species. Some adult fish eat fish larvae, sometimes including larvae of the same species.
Many bony fishes will eat members of their own species.
Disease
As in any animal population a variety of diseases can be responsible for bony fish death. These include bacterial, viral, and fungal infections, as well as tumors.
Parasites
Many types of internal and external parasites are common to bony fishes. Parasites are not typically a cause of death.
