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    Posted: 26/Feb/2012 at 10:21pm

Amazon Fishing News - Peacock Bass Coloration Explained

Research Paper Explains Peacock Coloration


A recently completed research paper explaining the variability in coloration of Cichla temensis, (the giant peacock bass) will be published in an upcoming issue of “Neotropical Ichthyology”, a peer reviewed scientific journal. Until recently, much of the fishing, management and scientific community has believed these variants to be two separate species, or subspecies, or even male and female differences.

The two extremes of peacock bass coloration are so wildly different that they go by separate names (“açu” and “paca” in Brazil and “Speckled” and “3-Bar” peacock bass in the U.S. sportfishing community). The new article explains the nature of the color variation and describes the research that led to the new understanding.

The project was undertaken because experienced peacock bass anglers have observed several phenomena that brought the established beliefs into question. First, not only are there two extremes in coloration, but anglers routinely encounter a whole range of intermediate patterns. Furthermore, anglers often catch fish involved in spawning activity, but these are always in the 3-bar form. The existing beliefs failed to explain this. In an effort to answer the questions raised by these observations, the research, performed under the joint auspices of Rutgers University (NJ) andThe University of Amazonas (Manaus), examined the question based on a new hypothesis. Could these variants all be the same fish undergoing seasonal changes related to their spawning behavior?

The project defined several coloration categories or stages (see the photos 1 - 4 in column A in the illustration) to serve as working tools and then examined the problem from three viewpoints.

First, it compared fish from each of the color categories to other species of peacock bass that shared the same water, using traditional taxonomic techniques (morphometrics). This confirmed that the variants didn’t belong to any of the other species. Next, the variants were subjected to DNA testing, which showed that they were indeed all members of the same species. Finally, using precise measurements and surgical and photomicrographic techniques, the study showed that these color and pattern variants were actually individual fish changing their coloration cyclically over the course of the Amazon’s yearly rainy and dry seasons. They gradually change from the speckled pattern to the 3-bar pattern as they prepare to spawn during the dry season, remaining in the 3-bar pattern until they finish guarding their babies.

The illustration shows the coloration variants as they change from one pattern to another in the four stages defined by the project. Column B shows the ovaries for the each of the stages. As a fish changes from the speckled (paca) to the 3-barred (açu) form, the ovaries enlarge, becoming thicker and fuller in preparation for spawning. By stage 4, they are large and distended. Column C shows photographs of the contents of the ovaries themselves, taken under the microscope. In the speckled stage, immature precursors to eggs (called oocytes) are visible. As a fish progresses through the stages, eggs begin to form and become mature. By stage 2, they begin to show nuclei (containing genetic material). In stage 3, the eggs begin to fill with the yolk that will provide the fry’s first food.

The eggs in stage 4 are large and fully mature and ready to be deposited on a submerged wood surface in the peacock’s large nest.

The study precisely weighed both ovaries and testes (collectively gonads) of two hundred fish in each of the coloration stages and showed that the mathematical relationship between gonad size and coloration stage is statistically significant. It is the same in both males and females, as is the color change itself.

This new information allows anglers to better understand these fish. For fishermen, this kind of knowledge is power. The better we know our quarry, the more effectively we can pursue and catch it.

Scientists know that color can have biological value. Before the spawn, the 3-bar coloration may help spawning fish find partners, saying “Look how beautiful I am, spawn with me!” Later on, like other brightly colored animals, they may be advertising the threat they pose. For example, brightly colored poisonous frogs are warning potential predators not to eat them; the results of that meal could be very bad for the predator. In the same fashion, brilliantly colored, fry-guarding peacock bass parents may be warning other fish to avoid trying to eat their babies; the results could be fatal for the would-be predator. If you’ve ever caught a big peacock under a fry ball with a prop bait, you’ll understand the accuracy of this threat immediately.

At the other color extreme, non-spawning fish are busy going about the business of eating and fattening up for the long fast associated with spawning.

They need to hunt effectively in the flooded forests bordering Amazon lagoons and backwaters. If you’ve ever looked into the dark, tea-stained waters at the edge of a lagoon with their submerged wood, dappled with leaf-filtered sunlight, you’ll understand exactly how a dark, speckled predator can disappear into the shadows.

Camouflage is a very effective hunting tool.

Most peacocks spawn near the end of the dry season when low water levels make more spawning area available. However, not all spawn at the same time and different spots have different relative depths, so you’ll likely see all of the coloration stages during a typical fishing trip. Now you can observe them with a new perspective.

New information also provides scientists with a platform from which to launch future studies - and further research is indeed underway.

The study was performed by, and the upcoming article was authored by Paul Reiss of Acute Angling with invaluable assistance, guidance and co-authorship provided by Dr. Ken Able of Rutgers and Dr. Tomas Hrbek, Dr. Izeni Farias and Mario Nunez of the University of Amazonas. Funding was primarily provided by Acute Angling, with generous assistance from many anglers who have contributed funds for equipment purchases for the study’s jungle laboratory.

The journal “Neotropical Ichthyology” can be found online and in print. The article will be available in its technical form on our website sometime after it has appeared in the journal.

Edited by Acute Angling - 26/Feb/2012 at 10:51pm
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