By Peter B. Moyle and Andrew L. Rypel

When both of us began studying the freshwater fishes of California, we independently discovered most fishes found in reservoirs and other highly altered habitats belonged to non-native species. Anglers and many fishery managers had pretty much accepted the reality that freshwater recreational fisheries are focused on non-native species, except for a few species of salmon and trout, mostly of hatchery origin. 

Especially important in the fisheries are ‘black bass’, a name given to all members in the sunfish family (Centrarchidae) that belong to the genus Micropterus. Bass fisheries command high economic and recreational value across the USA. Chen et al. 2003 estimated that in one year, a single trophy bass fishery in Texas generated $18.6M ($39.5M today) in economic activity, and supported at least 367 jobs. California lakes produce gigantic black bass (Fig. 1), including fish potentially weighing 20-25 lbs – sizes that put California in competition for world records. It is unclear why California bass grow to be so large but it could be related to comparatively low density populations overall in large reservoirs and lakes, long growing seasons, and abundant energy-rich prey, including hatchery-raised trout.

Historically, black bass in California consisted four non-native species: largemouth bass (M. salmoides), smallmouth bass (M. dolomieu), spotted bass (M. punctulatus), and redeye bass (M. coosae) (Moyle 2002). These species are now abundant and widespread in California. They prey on fishes and invertebrates, live in waters with a wide range of water quality, and can be challenging to catch (Moyle 2002). Largemouth bass and smallmouth bass are so favored by anglers that they now have global distributions in suitable waters (Fig. 2), thanks to frequent introductions, legal and illegal. In California, the history of introductions of all bass species is murky and confusing because of poor record keeping and the frequent treating of all species together as “black bass” (Dill and Cordone 1997). Increasingly, predation by bass species is regarded as an important factor contributing to declines of native fishes in California. Furthermore, and perhaps because of their warmwater thermal niche, bass tend to grow best during droughts (Rypel 2009). Thus, as climate change increases the duration and severity of droughts in California, novel conditions increasingly favor the black bass complex (Rypel 2021).

There remains much to learn about these fishes. Recent advances in genomic technology enables identification of cryptic species, hybrids and evolutionary pathways (e.g. Kim et al. 2022). These on-going examinations provide new and surprising insights into the evolution and ecology of the black basses. Here are some of the key findings:

• Actually, there are at least 19 species of Micropterus. Fourteen of them have been described and recognized (Page et al. 2023). Most are part of the Micropterus species complex present in the southeastern USA. This includes M. coosae, as the only redeye bass species introduced into California. These species are the epitome of “cryptic diversity” and are often difficult-to-impossible to distinguish with the naked eye. Hence their distinctiveness went unappreciated until modern genetic tools emerged. Most of these species evolved within the geologically old and unglaciated landscapes of the southeastern USA. 
• The Largemouth Bass is apparently two separate species: Florida Bass (M. salmoides) and Largemouth bass (M. nigricans). Previously, the Florida Bass was considered a subspecies, but has now been elevated to full species status. The Florida Bass is abundant in fresh waters in Florida and along the Atlantic and Carolina coasts (Kim et al. 2022). The two species have a wide zone of overlap in distribution in their native ranges and frequently hybridize as a result. In California, Florida Bass were widely introduced under the assumption that they were the same species of as Largemouth Bass, but grew faster and achieved larger sizes. Their introduction was generally regarded as a successful effort to improve recreational fisheries.
• The native range of Largemouth Bass (M. nigricans) includes much of the eastern USA, and it has also been widely introduced outside its native range. This was the ‘black bass’ species first introduced to California; however, records are confusing (Dill and Cordone 1997). In the 1960s and 1970s, CDFW introduced Florida Bass into waters already inhabited by Largemouth Bass. This stocking resulted in hybridization between the two species but the extent is poorly known (e.g. Moyle and Holzhauser 1978). Presumably, populations of Largemouth Bass in California are either M. nigricans or nigricans x salmoides hybrids. F1 Largemouth x Florida hybrids or ‘Tiger Bass’ have long been cultured for use in pond management and recreational fisheries. These fish are known for their large size, fast growth and aggressiveness.
• In California, the Spotted Bass lineage includes ‘true’ Spotted Bass (aka Kentucky Bass, M. punctulatus) and Alabama bass (M. henshalli). Both species seem to be widely distributed in California, the result of stocking by CDFW to improve fisheries in reservoirs and warm water streams statewide. The Alabama Bass appears to have been the most widely introduced of the two species in California. However, which species and hybrids are present today in a given reservoir or river requires genetic determination. 
• The International Game Fish Association (IGFA) recently revised their records and now recognizes an Alabama Bass caught from New Bullards Bar Reservoir in California during 2017 as the world record for the species (Taylor et al. 2024).

The diversity of ‘black bass’ species in California supports popular year-around fisheries but as bass continue to thrive and increase, native fishes decline. This problem is particularly acute for centrarchid basses. For decades, fish agencies have tried to improve bass fisheries, especially in reservoirs, in part to compensate for the loss of habitat for other native fishes like salmon as the result of dams and diversions. The strategy of increasing bass species diversity to support fisheries has been very successful, but it is at the cost of native fish populations, including salmonids. Reversing the trend in favor native fishes will be difficult, but research has shown that it can be done in the right circumstances, such as Putah Creek (Jacinto et al. 2023). 

Peter B. Moyle is a Distinguished Professor Emeritus at the University of California, Davis and is Associate Director of the Center for Watershed Sciences. Andrew Rypel is a Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences.

Further reading

Baker, W.H., R.E., Blanton, and C.E. Johnston. Diversity within the Redeye Bass, Micropterus coosae (Perciformes: Centrarchidae) species group, with descriptions of four new species. Zootaxa 3635(4): 379–401.

Chen, R.J., K.M. Hunt, and R.B. Ditton. 2003. Estimating the Economic Impacts of a Trophy Largemouth Bass Fishery: Issues and Applications. North American Journal of Fisheries Management 23: 835-844.

Jacinto, E., N.A. Fangue, D.E. Cocherell, J.D. Kiernan, P.B. Moyle, and A.L. Rypel. 2023. Putah Creek’s rebirth: a model for other degraded streams? https://californiawaterblog.com/2023/07/08/putah-creeks-rebirth-a-model-for-reconciling-other-degraded-streams/

Kim, D., A.T., Taylor, and T.J. Near. Phylogenomics and species delimitation of the economically important Black Basses (Micropterus). Scientific Reports 12: 9113 (2022). https://doi.org/10.1038/s41598-022-11743-2

Moyle, P. B., and N. J. Holzhauser. 1978. Effects of the introduction of Mississippi silverside (Menidia audens) and Florida largemouth bass (Micropterus salmoides floridanus) on the feeding habits of young-of-year largemouth bass in Clear Lake, California.  Transactions of the American Fisheries Society 107: 575-582.

Page, L.M., Bemis, K.E , Espinoza-Perez, H., Findley, L.T., Gilbert, C.R., Harsten, K.E., Lea, R.N, Mandrake, N.E., Mayden, R.L., Neighbors, M.A., Schmitter-Soto,, J.J.  & Walker, H.J. (2023) Common and Scientific Names of Fishes from the United States, Canada, and Mexico. 8^th edition. American Fisheries Society Special Publication 34. American Fisheries Society, Bethesda, Maryland, 243 pp.

Pinter, N., J. Lund, and P. Moyle. 2019.  The California water model: resilience through failure. Hydrological Processes2019: 1–5. https://doi.org/10.1002/hyp.13447

Rypel, A. L. 2009. Climate–growth relationships for largemouth bass (Micropterus salmoides) across three southeastern USA states. Ecology of Freshwater Fish 18(4):620-628.

Rypel, A.L. 2021. Do largemouth bass like droughts? https://californiawaterblog.com/2021/05/02/do-largemouth-bass-like-droughts

Silliman, K., H. Zhao, M. Justice, W. Thongda, B. Bowen, and E. Peatman. 2021. Complex introgression among three diverged largemouth bass lineages. Evolutionary Applications 14: 2815–2830 (2021).

Taylor, A.T., Z.L. Bellapigna, and B.G. Pohlot. 2024. Updating angling records to advance sport fish conservation: a case study of IGFA’s black bass world records. Fisheries 49: 221-232.

Tringali, M.D., J.M. Long, T.W. Birdsong, and M.S, Allen, editors. 2015. Black Bass Diversity: Multidisciplinary Science for Conservation. American Fisheries Society Symposium 82:685 pp.