Ambloplites rupestris

Geographic Range

Rock bass ( Ambloplites rupestris ) are distributed throughout North America. They are native to the North Atlantic region of the United States and the St. Lawrence, Great Lakes, Hudson Bay, and Mississippi River drainages, as well as northern to southern Georgia and northern Alabama and Missouri. Rock bass thrive in areas of the east-central part of the United States. Although they are native to these areas, many introductions have been made. From 1889 to 1936, the United States Fish Commission introduced rock bass to Atlantic drainages and some western states. Rock bass were introduced to areas of the Atlantic drainages, from New Hampshire, south to the Roanoke River in Virginia and North Carolina. As for the western states, rock bass have made it to states such as California, Washington, Colorado, and even Wyoming. Rock bass have also been introduced in other regions. In Europe, rock bass were introduced in countries such as England and France in the 1880’s.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
  • native native

Habitat

Rock bass are found inhabiting aquatic biomes such as rivers, streams, lakes, and ponds. These aquatic biomes are freshwater, often heavily vegetated to provide cover from predators. These fish also thrive in biomes with temperatures ranging from 10 to 29 degrees Celsius. Rock bass are most commonly distributed in regions that supply a habitat of rocky or sandy characteristics in clear water. In regions where rock bass are introduced such as Europe, ecologists have found their habitats to be slightly different from North American residents. Rock bass distributed in Europe prefer similar habitats, but avoid areas of fast moving water.

• Habitat Regions
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

Physical Description

Rock bass are part of genus Ambloplites , meaning “blunt shield,” and the species name rupestris refers to their preference for being “among the rocks.” Similar to other sunfish, rock bass can be distinguished by the five to seven spines located on the anal fin along with nine to eleven soft anal rays. Rock bass also have spines located on their much larger dorsal fin, with 10 to 13 spines and 11 to 13 soft dorsal rays. Rock bass have distinguishable dark spots on each scale that are aligned in rows around the lateral line, continuing down towards the ventral side. Starting with their back, rock bass are dark green or brownish, fading to a lighter green, and slowly fading to whitish green or yellow towards their ventral side. Their fins have a yellowish brown tint, with a black spot on the tip of the gill plate. They are relatively small, averaging about 20 to 25 cm long and very rarely reach one kilogram, although the largest recorded rock bass was 3 kg. Rock bass have large mouths and bright red eyes, which give them the nickname “redeyes.”

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

Three to four days after spawning, the eggs begin to hatch. At hatching, the mean length of rock bass larvae is about 5.5 mm. As the larvae grow, melanophores (connective-tissue cells containing melanin, which gives them their color) also begin to develop at about 6.8 mm. By about 6.9 mm, the larvae begin to develop caudal fin rays, and dorsal, anal, and pectoral fin rays at about 8.6 mm in length. Finally, pelvic fin rays begin to develop at about 13.5 mm in length. As the maturation cycle of the larvae continues, by the first year, young rock bass grow to about 5 cm in length, reaching 10 cm by year two, and up to 18 cm by year three.

Reproduction

Rock bass are polygynandrous, in which both females and males have multiple mates during the breeding season. Rock bass spawn in the spring and, in some cases, spawn again in the early summer with another mate. When attracting a mate, male rock bass find a suitable area and build a nest. Circling inside the newly prepared nest, the male awaits a mate. Without courtship displays, the female enters the nest and joins the male in his circular behavior. Both the female and male simultaneously release their sperm and eggs into the nest. The female's role in spawning is over after they release eggs and they are able to leave the nest and mate with another male, although they sometimes choose to remain near the exterior of the nest. Male rock bass guard and protect the nest using circling behaviors until the fry hatch.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Similar to the spawning cycle of smallmouth bass , rock bass spawn in areas of shallow water. The spawning cycle of rock bass occurs in the spring and into the summer months of June, as the water temperature reaches between 13 to 15 degrees Celsius. Rock bass reach sexual maturity at about 2 to 3 years of age. Male rock bass prepare the nest for spawning. Their nests are circular bowl-shaped depressions, approximately 20 to 30 cm in diameter. Using their tail, male rock bass are able to clear areas of debris to produce their nest. Without male courtship, females enter the newly-made nest and spawn, releasing approximately 500 to 5,000 eggs depending on the female's size. After fertilization by the male, the newly spawned eggs are guarded by male rock bass in the interior of the nest, which consists of a 20 to 30 cm area. While guarding the eggs, males turn darker in color and continue their circling behavior, which helps protect the eggs from predators. The eggs begin to hatch 3 to 4 days after spawning and the fry leave the nest approximately 9 to 10 days after hatching. Approximately 33% of rock bass nests are unsuccessful due to predation.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Male rock bass show parental care by fanning the nest with their pectoral fins and guarding and protecting the nest by using circling behaviors after spawning with the female. These behaviors continue for several days, protecting the offspring from predators in hopes of reaching a goal of maximum fitness. After females lay eggs in the nest, their parental effort is complete.

• Parental Investment
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
  • protecting
    • male
• pre-independence
  • provisioning
    • male
  • protecting
    • male

Lifespan/Longevity

Rock bass have an average lifespan of about 5 to 8 years in the wild. This average is obviously influenced by the level of predation and food supply in the environment. It has been reported that the maximum lifespan of a rock bass in captivity was 18 years.

Behavior

During spawning, male rock bass do not eat. Male rock bass guard the nest of the newly spawned eggs. This nest becomes their home range, spanning between 20 and 30 cm in diameter. To protect the nest from predators, they perform circling behaviors. Males are very aggressive during spawning season. When faced with a territorial intruder, they race towards it with spread opercles or display an open mouth. In the winter months, rock bass can be found in schools and slowly go their separate ways as spring approaches for spawning activity.

• Key Behaviors
• natatorial natatorial
• motile motile
• territorial territorial
• social social

Home Range

Besides the nest territory that males defend, no other home ranges have been reported.

Communication and Perception

Fish use chemical signals to communicate and perceive their environment. Rock bass use chemoreception for a number of communication and perception tasks. These tasks consist of locating prey, identifying opposite sexes, identifying other species, identifying predation threats and how to avoid these predators, differentiating between their young, signaling for migration from others, and even identifying where they are in comparison to their habitat. Rock bass use tactile characteristics or the sense of touch with body parts such as their large, bass-like mouth and even visual characteristics such as their big eyes or “goggle eyes,” which is another common nickname of rock bass.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Rock bass prey on various aquatic species such as plants located around their highly vegetated habitat. Rock bass also prey on small crustaceans like crayfish , insects such as small larvae, and smaller fish, including those of their own species.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
• omnivore omnivore

• Animal Foods
• insects
• aquatic crustaceans

Predation

Predators of rock bass include of other, larger adult rock bass, northern pike , muskies , walleyes , largemouth bass , and even humans . These predators prey on adult and young rock bass. To avoid these predators, rock bass depend on their cryptic coloration, staying camouflaged in their environment.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Rock bass feed on insects , aquatic crustaceans , and smaller fish. As a result, the populations of these organisms are suppressed so that their population densities are at an acceptable level. Rock bass are also hosts in their ecosystems. Copepods , a small group of crustaceans that have a parasitic role with rock bass, such as anchorworms , depend on rock bass. Anchorworms are external parasites that embed into the skin of the fish and damage and ultimately decrease the longevity of rock bass.

Economic Importance for Humans: Positive

Rock bass, along with other bass species, such as smallmouth bass , largemouth bass , and spotted bass , are all sport fish. With competitive tournament events and even recreational events, bass fishing has evolved into a multi-billion dollar industry. For example, 33 million people of age 16 and older engage in the activity of fishing and spend 48 billion dollars a year to do so. These sportsmen spend this money on fishing guides and services, equipment, apparel, licenses, restaurants, gas, boats, and more. Fishing also supports 828,000 jobs in the United States; many of these jobs involve fishing for species such as rock bass.

• Positive Impacts
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

Environmental impacts may result from sport fishing for rock bass and other species. For example, pollution from boats, such as oil and gas leaks, as well as littering by sportsman can take an economic toll on the efforts to maintain clean and healthy ecosystems.

Conservation Status

Introduced into many drainages in the United States, rock bass have flourished in their environments. As a means of conservation, rock bass are successfully surviving in their environments and are listed as a species of "least concern" on the IUCN red list. Rock bass do not require any special monitoring or conservation management plans because of their population stability. However, as a sport fish, they are managed to some extent. Even though they are not a fish many people prefer to eat, there are slot limits (required lengths) on different bodies of water, which regulate whether people can keep these sport fish. Also, artificial nests and nursery/artificial ponds are management tools developed to maintain populations of rock bass.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Brendan Schnell (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

References

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