Rock Bass, Ambloplites rupestris
Rock Bass, Ambloplites rupestris. Fish caught from the Yahara River, Madison, Wisconsin, July 2007. Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.
Rock Bass, Ambloplites rupestris. Fish caught from the Yahara River, Madison, Wisconsin, July 2007. Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
Rock Bass, Ambloplites rupestris. Fish caught from the Yahara River, Madison, Wisconsin, July 2007. Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).
The Rock Bass, Ambloplites rupestris, is a member of the Sunfish or Centrarchidae Family, also known as the Google Eyes and the Red Eye, and in Mexico as lobina de roca. Globally, there are four species in the genus Ambloplites, of which only this species is found in the streams, rivers, lakes, and ponds of Mexico’s freshwater systems.
The Rock Bass has a very deep and moderately compressed body that is 32% to 37% of total length and deepest at the dorsal fin origin. They are similar in appearance to a small Smallmouth Bass. They are covered with small scales, dark green to brown dorsally, transitioning to yellow ventrally. They have dark spots on each scale that align in rows around the lateral line and extend ventrally. They have a black spot on the gill cover and bright red eyes. Their fins are yellowish-brown. Juveniles are pale or yellow-green with irregular barring and blotching in black. They have a large, terminal, slightly oblique mouth with a protruding lower jaw equipped with small conical teeth. The anal fin has 5 to 7 spines and 9 to 11 rays; the caudal fin is straight; the dorsal fin is continuous with 10 or 13 spines and 11 to 13 rays; and the pectoral fin has 14 or 15 rays. They have less than 20 gill rakers on the first arch.
The Rock Bass is found in rocky areas in shallow clear water without turbidity or siltation, in lakes, rivers and streams within vegetated and bushy areas at depths up to 21 m (69 feet). They reach a maximum of 43 cm (17 inches) in length and 1.4 kg (3 lbs 2 oz) in weight. As of January 1, 2023, the International Game Fish Association world record stood at 1.36 kg (3 lbs 0 oz), with the fish caught in the Pennsylvania in 1988. They require vegetation for protection against predation. They also prefer water temperatures between between 10oC (50oF) and 29oC (84oF). They are opportunistic feeders that consume aquatic insects, insect larvae, crayfish, snails, other small invertebrates and small fish. In turn they are preyed upon by Black and White Crappie, Largemouth Bass and Smallmouth Bass, as-well-as sea birds and otters, raccoons, turtles, and humans. They utilize their cryptic color as their primary defense but with fins extended they are hard to swallow. Reproduction is oviparious and polygynandrous (promiscuous) and occurs continually when water temperatures are in excess of 12oC (54oF). During this period males become highly territorial and very aggressive. They build highly visible nests in very shallow sand or gravel substrate. Each female will deposit between 500 and 5,000 eggs in the nest where they are immediately fertilized by the males and adhere to the substrate. The males remain on the nests to provide care and defense of the eggs for about 14 days. The eggs hatch into fry in 3 or 4 days and will remain on the nests for an additional 9 or 10 days. Approximately 33% of the fry die due to predation. The females will quickly find a new nest and a new male as each male will spawn with several females in one nest each year. Young fish feed on plankton, but as they grow their diet shifeets to aquatic insects and insect larvae. Rock Bass are frequently seen in groups. They have life spans of up to eighteen years.
The Rock Bass is similar to several other sunfishes, including the Bluegill, Lepomis macrochirus and the Warmouth, Lepomis gulosus, but it is the only one that has 6 anal fin spines and a bright red eye. They differ from members of the Pomoxis Genus, the Crappies, by having more than 10 dorsal spines.
The Rock Bass is native to the St. Lawrence River and Great Lakes, Hudson Bay, and Mississippi River basins, from Quebec to Saskatchewan, south to the Savannah River drainage, Georgia, northern Alabama, and Missouri. They have been intentionally stocked throughout the United States (primarily as a sportsfish) and in Mexico (primarily for food). They are currently present in the majority of freshwater systems of Mexico’s Central Plateau.
From a conservation perspective the Rock Bass is currently considered to be of Least Concern with stable, widely distributed populations. They have been raised in fish hatcheries and introduced extensively throughout the southern United States and into northern Mexico and other countries as a sportsfish and a food fish. They can quickly adapt to new environments and quickly become a highly invasive pest causing overcrowded conditions and destroying native populations. In the United States they are subject to targeted fish tournaments to help control their populations. They are a popular recreational angler foe on light tackle and flyrods. They are, however, considered to be a marginal food fish. They are also utilized by the aquarium trade including public aquariums.