Warmouth, Lepomis gulosus
Warmouth, Lepomis gulosus, Male. Fish caught from the Rend Spillway, Benton, Illinois, June 2016. Length: 12.8 cm (5.0 inches). Catch, photograph and identification courtesy of Ryan Crutchfield, Tampa, Florida.
Warmouth, Lepomis gulosus, Male. Fish caught from the Mukwonago River, Wisconsin, May 2012. Length: 15.0 cm (5.9 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.
Warmouth, Lepomis gulosus. Fish caught from the Eastmanville Bayou, Allendale, Michigan, December 2016. Length: 16.0 cm (6.3 inches). Catch, photograph and identification courtesy of Marc Eberlein, Grand Rapids, Michigan.
The Warmouth, Lepomis gulosus, is a member of the Sunfish or Centrarchidae Family, and is known in Mexico as mojarra golosa. Globally, there are thirteen species in the genus Lepomis, of which seven are found in the streams, rivers, lakes, and ponds of Mexico’s freshwater systems.
The Warmouth has a heavy bass-like body that is strongly compressed laterally with a depth that is 44% to 48% of standard length. They have a dark greenish-brown mottled coloration dorsally, transitioning to golden ventrally. They have 3 to 5 reddish-brown streaks radiating from the eyes, and a dark colored gill flap. They are dimorphic with the males having a bright-orange spot at the base of the dorsal fin. Breeding males have bright red eyes. The juveniles are less colorful than the adults, allowing them to blend into the vegetation for protection against predation. The head has a large terminal mouth extending to the middle of the eyes, with a lower protruding jaw equipped with lingual and palatine teeth. Their anal fin has 3 spines and 9 or 10 rays; their caudal fin has equal lobes; their first dorsal fin has 6 to 13 spines; their second dorsal fin has 9 or 10 rays, and their pectoral fins have 13 or 14 rays. They have 9 to 12 long thin gill rakers. They are covered with ctenoid scales.
The Warmouth is a non-migratory demersal freshwater species that is found in slow-moving or still waters, including streams, rivers and ponds with a soft substrate and dense beds of submerged, floating, or emergent aquatic vegetation or other dense cover such as stumps, brush or boulders. They can survive in polluted streams with low oxygen levels where other sunfishes cannot. They spend their time hiding around rocks, submerged logs, plants, and other things that provide cover to avoid predation. They reach a maximum of 31 cm (12 inches) in length and 1.1 kg (2 lbs 7 oz) in weight. As of January 1, 2023, the International Game Fish Association world record stood at 1.10 kg (2 lbs 7 oz), with the fish caught in Holt, Florida in 1985. They can be found in waters with temperatures between 10oC (50oF) and 34oC (93oF). They are lie-in-wait ambush predators that prey upon insects, crayfish, fishes and shrimp. The juveniles consume microcrustaceans and aquatic insect larvae. In turn they are preyed upon by alligators, birds, larger fish, water snakes, and turtles. Reproduction is oviparous and polygynandrous (promiscuous) and occurs continually when water temperatures are in excess of 21oC (70oF). During this period, males become highly territorial and very aggressive. They build highly visible nests in very shallow sand or gravel substrates but not in colonies. Each female, based on size, will deposit into the nest, between 4,000 and 62,000 adhesive eggs that attach to the substrate. Fertilization is external and males remain on the nest for 3 to 5 days until the eggs hatch. The young remain on the nest for up to another 5 days and then scatter to hide within benthic substrate to avoid predation. The male will then try to attract another female to his nest. They are known to hybridize numerous fish including the Black Crappie, Pomoxis nigromaculatus, the Bluegill, Lepomis macrochirus, the Green Sunfish, Lepomis cyanellus, and the Largemouth Bass, Micropterus salmoides. Young fish feed on plankton, but as they grow, their diet shifts to aquatic insects and insect larvae. They have lifespans of between three and eight years in the wild.
The Warmouth can be confused with the Green Sunfish, Lepomis gulosus (dark bars on the cheeks, a black spot at the base of the dorsal fin, yellowish-white fin borders), and the Rock Bass, Ambioplites rupestris (5 to 7 anal spines). The Warmouth is also larger than the Green Sunfish and the Rock Bass.
The Warmouth is a native to eastern North America and can be found in the majority of rivers that drain into the Atlantic Ocean. They have been widely introduced throughout the United States. In Mexico they are currently found in the freshwater systems of the States of Chihuahua, Coahuila, Nuevo León and Tamaulipas. Being highly invasive, sooner than later they will be found in all freshwater systems of Mexico.
From a conservation perspective the Warmouth is currently considered to be of Least Concern with stable widely distributed populations. They have been introduced on a broad scale both intentionally, primarily for sportfishing via aquarium releases, and by accident, as they are difficult to identify in the field. Throughout the United States the Warmouth is now considered to be a highly invasive pest that destroys native populations and other forms of life including frogs and salamanders. Established populations have been both difficult and expensive to control. Their purchase and sale in many states is banned. The Warmouth is considered to be an important recreational fish that is actively pursued for its catchability and food value noting that their meat is strongly flavored. They are a favorite of cane pole fishermen. They are also utilized as laboratory animals and by the aquarium trade.