Fish Nest Associates

The bluehead chub (Nocomis leptocephalus) is a keystone species in piedmont and mountain rivers and streams of southeastern North America.  Dozens of species of shiners spawn and lay their eggs in bluehead chub nests.  Without the existence of bluehead chubs most of these species would probably become extinct.  Bluehead chubs and shiners are members of the minnow family, known scientifically as the Cyprinidae, and bluehead chubs are 1 of the largest minnow species, growing up to 8 inches long.  Bluehead chubs make large gravel nests and aggressively protect their young.  They bury their eggs with large pieces of gravel and in the process bury and protect the eggs of other minnow species.  A complex ecosystem inhabits bluehead chub nests. Many macroinvertebrates live in bluehead chub nests alongside the minnow eggs.  Snails, clams, and the larval stages of dragonflies, dobsonflies, caddisflies, and beetles use the bluehead chub nests for shelter.  Salamanders and darters prey on the invertebrates entering and exiting the nests.  Scientists believe shiners and bluehead chubs both benefit from the congregation of eggs and hatchling fish, referring to the relationship as mutualism.  The great abundance of eggs from several different species dilutes the losses to predators, and more young of each individual species survives.

Bluehead chub range map.

Bluehead chub.

Rainbow shiner (Notropis chrosomus).  Some shiners can get quite colorful.

Many other species of fish associate in the same nests.  Rough shiners (Notropis baileyi), saffron shiners (N. rubicroceus), and greenhead shiners (N. chlorocephalus) spawn in creek chub nests.  Redfin shiners (Lythurus umbratalus) spawn in green sunfish (Lepomis cyonellus) nests.  All of these associations result in increased reproductive success for both species.  Some shiners will use central stoneroller nests, but prefer chub nests and will move their spawning activity to bluehead chub nests, if they become available.

The evolution of fish nest association must be very ancient.  It seems likely the host fish evolved first, and the species of fish using the host’s nest lost their ability to make their own nests when they came into contact with the larger  host species because the host could build bigger nests that offered more protection.  Host species are usually larger and better able to defend the nest than the smaller minnows, but they benefit too from the sudden population explosion of potential food for predators that might otherwise eat their hatchlings.

Reference:

Johnston, Carol

“Nest Associate in Fishes: Evolution of Mutualism”

Behavioral Ecology Sociobiology 35 1994

Swartwout, M.; F. Keating, and E. Frimpas

“A Survey of Macroinvertebrates Colonizing Bluehead Chub Nests in a Virginia Stream”

Journal of Freshwater Ecology 2016