Happy Fish Friday, everyone!
This week I want to highlight a common but often misidentified fish. I present to you the Rock Bass (Ambloplites rupestris)! Also known as the goggle-eye or red-eye, depending on where you live. Their defining characteristics are a laterally compressed and oblong body. They have a large head, a very large mouth, with a projecting lower jaw. Their eyes are a bright red or orange, and the scales below the lateral line have distinctive black dots that form rows. The body is brown to olive-green with 4-7 dark saddle bands across the head and back, the anal fin has 5-7 spines, most often is 6. There is a dark teardrop below the eye. Juveniles appear almost marbled. These fish commonly grow to roughly 8 inches but have been known to reach a foot in length.
Profile of a Rock Bass from Big Walnut Creek, Ohio. Shows all identifying characteristics listed above. Credit: Paul DeRolf
Rock Bass primarily reside in large creeks and small rivers with clear water and rocky substrates (hence their name). They also are found around large boulders, in root wads covering undercut banks, and beds of water willow that deflect flow. In natural lakes, Rock Bass prefer gravel bottoms, rocky shorelines, and vegetation beds.
A pair of juvenile Rock Bass from Wildcat Creek, Indiana. Credit: Paul DeRolf
The Rock Bass is a mid-sized predator with a carnivorous diet. As ambush predators, they utilize the habitat listed above as cover to lie in wait for food. They primarily eat smaller fish, often a variety of minnows and shiners, crayfish, and other aquatic insects. They have also been known to consume their own young at times. Their large mouth allows them to eat food whole.
Spawning occurs around April through June when the water temperatures are in the mid to upper 50s. Males turn nearly jet black and sometimes develop a gold speckling across their bodies. Like other sunfishes, Rock Bass build a circular nest over gravel substrate where there is little flow. These nests are guarded vigorously by the highly territorial males. Females enter the nests, where they release their adhesive eggs, between 2,000 and 11,000, into the gravel. The male protects the eggs until they hatch, roughly five days, and then guards the young until they can swim away.
A large male Rock Bass in spawning coloration from the West Branch DuPage River, Illinois. Credit: Paul DeRolf
Rock Bass have a large native range in North America. Their range covers the St. Lawrence River, across the Great Lakes, and most of the Upper Mississippi River basin. Unfortunately, much like their cousins, they have been moved well outside this native range. They have been introduced into numerous states and waterways, even into Mexico, the UK, and France! Most of these were intentional stockings done by state agencies in the early to mid-1900s to increase sportfishing. Due to this, they have severely impacted the populations of multiple native species.*Even though they are common, please do not transplant these or any other species outside their current range.*
Overall native range for Rock Bass in North America. Credit: roughfish.com
Complete range of Rock Bass with native areas in orange and introduced areas in maroon. Credit: USGS NAS program.
For as long as I can remember, the Rock Bass has been constantly misidentified for its cousins, the Green Sunfish and Warmouth. The easiest way to distinguish them is by the anal spines, 5-7 for Rock Bass and 3 for Green Sunfish and Warmouth. Rock Bass also lack streaks along their face, whereas Green Sunfish have blue and Warmouth have brown.
Thanks to their aggressive feeding habits Rock Bass can make easy targets while fishing. Their personalities also make them excellent for home aquariums. As long as you provide them with enough room, proper cover, and a healthy diet, they will be some of the most active fish. No matter how you decide to see them, please remember to make sure that you enjoy, protect, and enhance our freshwater ecosystems!
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