First Look at the Reproductive Biology of the Endangered Tropical Fish Betta channoides  

Author(s): Thomas Lopez

Mentor(s): Valerie Olmo, Biology

Abstract
Betta channoides is an understudied and underprotected fish from Borneo. The IUCN categorizes this fish as Endangered due to habitat loss, and its population in the wild is declining. Despite this situation, there is no legislation protecting this species anywhere in the world, and no research dedicated to this species has ever been published. This project addresses this knowledge gap by documenting the reproductive biology of Betta channoides. A male-female pair were brought from their habitat in Borneo to a lab setting in Exploratory Hall. Investigators housed them in aquaria which simulated their natural environment in order to induce and study their behaviors as closely as possible in captivity. These measures were successful in encouraging the pair to spawn, and investigators successfully documented their reproduction for the first time in a scientific setting. Betta channoides was shown to use a unique color-changing ability to communicate with conspecifics, and used this trait in an elaborate 3-hour mating ritual not seen in other Betta species. Investigators also confirmed that the species is a paternal mouthbrooder, recording a brooding period of 14 days. Behavioral evidence also suggests that B. channoides may engage in bi-parental care of the offspring, a behavior never observed in other Betta fish. Overall, these findings challenge established knowledge about B. channoides and the genus as a whole, suggesting that this fish may be much more social in nature than previously thought. Investigators hope to continue studying the reproduction of this species so that biologists and conservation workers alike may learn from their evolution.
Audio Transcript
Hello, my name is Tom Lopez and I’m currently a junior biology student at George Mason University. Today I will be presenting my work on the reproductive biology and conservation of an endangered tropical fish.

Betta channoides is a small understudied fish endemic to the province of East Kalimantan in Indonesian Borneo. It is related to the common Betta or Siamese Fighting Fish often seen in pet stores, but only distantly. This species occurs exclusively in the middle Mahakam river basin, where it inhabits the shallow jungle pools that tassel the river’s edge. Unfortunately, it is severely imperiled throughout its range.

The IUCN Red List categorizes this fish as Endangered, and it is primarily threatened by the mass clearing of forests for the construction of palm oil plantations. As of 2019, its population trend in the wild is sharply decreasing. Representing one of only two species within its taxonomic rank, this species is highly endemic and unique to this part of the world. Its extinction would represent the erasure of an entire species complex within the genus Betta. All of these factors combined makes Betta channoides a conservation priority; despite this, this fish is severely understudied and underprotected. Despite its IUCN listing, this species is not protected by any legislation anywhere in the world. The IUCN report is one of just a handful of mentions in scientific literature, with no dedicated research ever conducted on this species. This knowledge gap is why I decided to focus on Betta channoides for my research. I have had the pleasure of working hands-on with this little fish for over a semester; this presentation will explore my discoveries while keeping them in the lab.

Coming at the issue from a conservation standpoint, I decided to focus on the reproduction of this species. Scientific literature currently states that Betta channoides is a paternal mouthbrooder, which means that the male fish holds its offspring within his mouth for a portion of their development. However, this assertion is only attributed to a single source, which assumes this fact given its close genetic relation to another mouthbrooding betta.. After realizing this, I decided to design this project as an ex-situ conservation breeding program; my goal was to induce and record their breeding behavior and parental care for the first time.

To achieve this, I acquired two individuals collected from their habitat in Borneo- a male and a female. I kept them in an aquarium which simulated their natural habitat- a shallow, murky pool filled with sand and leaf litter from jungle trees. By doing this, I hoped to encourage natural behaviors from the fish as accurately as possible in a captive setting.

Before I could breed them successfully, however, I had to observe and learn about their behavior. As it turns out, Betta channoides possess an elaborate and meticulous form of communication that they use for reproducing. This fish can change its coloration and patterning at will. The male fish is normally brown when calm, but is capable of flushing an intense red when excited, aggressive or looking to breed. The female fish has less dramatic colors, but a significantly higher degree of control over her pattern, able to appear solid yellow, horizontally striped, vertically banded, or even varying combinations of these patterns. Most notable is the “bee stripe” pattern exhibited only when she has eggs. During this phase, the female fish grows a large white spot on her left lateral flank, presumed to be an egg spot. Once I learned this language of colors, I was able to introduce them to one another at the right time for them to spawn.

The male fish approaches the female first and uses his coloration to initiate their tedious mating ritual. He repeatedly opens his mouth and flares his fins; if the female reciprocates, she will do the same, repeatedly arching her back and flashing her egg spot. They engage in this dance for several minutes before the female begins laying eggs. She lays a single egg at a time; after laying, she picks the egg up with her mouth and initiates an embrace with the male fish. It is at this point where it is believed that the male fertilizes the egg. After this, the female will engage in an unusual behavior where she repeatedly spits out the newly fertilized embryo, only to suck it back into her mouth. Each time she does this, the male will attempt to grab the embryo from her; this will go on until the male successfully takes the embryo. After this, the process repeats for each new egg. This elaborate ritual goes for an average of three hours, taking a considerable amount of time and energy to complete.

After mating, the male will hold the clutch of embryos in his mouth for the next 14 days. During this period, he does not eat, and barely moves. The male and female stay near each other at all times, but the female was not observed contributing to the care of the offspring. For now, the nature of this relationship is unknown. Within his mouth, the embryos develop into larvae, then metamorphose into fully-developed juveniles called fry. This process has never been documented in Betta channoides and is incredibly difficult to observe due to their mouthbrooding behavior; as such, it is currently unknown how these offspring survive in there for so long.

After 14 days, the male releases 13 tiny, 4mm long juveniles into the water column. They are immediately able to swim and feed themselves, so the parents no longer provide any care for them. Despite this, neither the male nor the female have been observed being aggressive with the young; this, combined with their complex communication, points to Betta channoides being a much more social species than seen in other Betta fish.

This is all the information that has been compiled so far. By keeping Betta channoides in an environment which closely resembles their habitat, we were able to successfully induce, observe, and record their breeding behavior multiple times. This is the first time that this species; reproduction has been characterized in a scientific study. Throughout the process, we confirmed that Betta channoides was a paternal mouthbrooding fish; we also made several discoveries which challenge established knowledge about Betta fish as we know them. We have compiled evidence that Betta channoides may be the only Betta fish which exhibits bi-parental care, and its ability to communicate with colors point to an active social life living in high densities. More research must be done in their habitats to learn more about these reclusive fish- and more importantly, work must be done to stop these little gems from going extinct before we can learn from them. By the end of the semester, several questions were answered, but even more remain; I am excited to keep working with this beautiful fish and discover more about them for the scientific and conservation communities to learn from.

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