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Influence of Visual and Chemical Cues on nest and bower-building behaviours of Coptodon rendalli (Boulenger, 1905) and Ooreochromis shiranus (Boulenger, 1905) in Fibre tanks

This study demonstrates that both visual and chemical cues significantly influence the nest- and bower-building behaviors of *Coptodon rendalli* and *Oreochromis shiranus*, with optimal structure dimensions observed when males and females are separated by a fine net and when water contains specific levels of soil substrate-treated cues, providing valuable insights for improving hatchery breeding conditions.

Original authors: Luckson Solicitor Maurice Gondwe

Published 2026-07-07

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Luckson Solicitor Maurice Gondwe

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine two different types of fish, Coptodon rendalli and Oreochromis shiranus, living in a controlled environment like a giant, clear aquarium. These fish are like nature's architects; before they can have babies, the males need to build special homes. One species builds a "nest" (a pit for eggs), and the other builds a "bower" (a decorative sand structure to attract mates).

The researchers wanted to know: What makes these fish want to build these homes, and how big will they make them? They tested two main "triggers": what the fish can see and what they can smell (or taste) in the water.

Here is a simple breakdown of what they found:

1. The "See-You-There" Test (Visual Cues)

The researchers set up three scenarios to see how the fish reacted to seeing a potential mate:

Scenario A: Males and females are in the same tank, swimming together.
Scenario B: Males and females are in completely separate tanks.
Scenario C: Males and females are in the same tank, but separated by a fine mosquito net. They can see each other clearly, but they can't touch or swim together.

The Result:
The fish built their biggest and most impressive structures in Scenario C (the net separation).

Think of it like this: Imagine you are trying to impress someone at a party. If you are right next to them, you might get distracted or nervous. If you are in a different room, you can't see them at all. But if you are in the same room with a glass wall between you, you can see them clearly without the chaos of direct contact. This "just out of reach" view seemed to drive the males to work the hardest.
The Difference: The Coptodon rendalli fish built significantly larger nests than the Oreochromis shiranus built bowers. The Coptodon species seemed to be more "visual," reacting strongly to just seeing a female to start construction.

2. The "Scent of Home" Test (Chemical Cues)

Next, the researchers tested if the water itself could trigger building. They took water that had been mixed with soil (sand) and added different amounts of it to the fish tanks.

The Levels: They tested tanks with no soil water (control), a little soil water, a medium amount, and a lot of soil water.

The Result:

The Sweet Spot: The fish built the largest structures when the water had a medium amount of soil water (specifically, four cups of soil-water mix).
Too Little or Too Much: If there was no soil smell, they built smaller homes. If there was too much soil water (six cups), the buildings actually got smaller again.
Think of it like this: It's like baking a cake. If you add no vanilla, it tastes bland. If you add a perfect amount, it's delicious. But if you dump in the whole bottle of vanilla, it becomes unpalatable. The fish needed a "just right" amount of soil scent to feel like it was time to build a big home.
The Difference: Again, the Coptodon rendalli was more sensitive to these smells and built bigger structures than the Oreochromis shiranus.

3. Where Do They Build?

One surprising discovery was that the fish didn't need to build their homes right next to the female. Even when the soil was placed far away from the female fish, the males still built their nests and bowers there.

The Takeaway: The fish don't need to be "hugging" the female to get the job done. They just need the right visual or chemical signals to know it's time to start construction.

Why Does This Matter?

The paper concludes that if you are trying to breed these fish in a hatchery (a fish farm for babies), you shouldn't just throw them in a tank. To get them to breed successfully:

Visuals matter: Let the males see the females, perhaps through a barrier, to encourage them to build.
Smells matter: Add a specific amount of soil-water to the tank to trigger the building instinct.
Don't overdo it: Too much soil water actually stops them from building big homes.

In short, these fish are like picky homebuyers: they need to see the "For Sale" sign (the female) and smell the fresh paint (the soil water) in just the right amount before they decide to build a house.

Technical Summary: Influence of Visual and Chemical Cues on Nest and Bower-Building Behaviours of Coptodon rendalli and Oreochromis shiranus

Problem Statement
While nest and bower building are critical reproductive behaviors in cichlid fish, serving as indicators of male quality and mechanisms for brood survival, there is a paucity of research examining how specific environmental cues induce these behaviors in farmed tilapia species. Specifically, the extent to which visual and chemical cues influence the construction of nests (in Coptodon rendalli) and bowers (in Oreochromis shiranus) under controlled hatchery conditions remains poorly understood. This knowledge gap limits the ability to optimize breeding environments for improved hatchery management.

Methodology
The study was conducted over five months (October 2022–February 2023) at the Bunda Aquaculture Farm in Lilongwe, Malawi, utilizing a completely randomized experimental design. Two distinct experiments were performed:

Experiment I (Visual Cues): Eighteen 1,000-liter circular tanks were used to test the role of visual contact. Treatments involved stocking male and female broodstocks (1:2 ratio) in three configurations: (a) together in the same tank, (b) in separate tanks, and (c) in the same tank separated by a fine mosquito net. Sandy substrates were provided for construction.
Experiment II (Chemical Cues): Thirty-two 200-liter circular tanks were used to assess the impact of chemical cues derived from soil substrates. Four levels of chemical stimulation were tested: a control (well water only) and three treatments involving the addition of soil-substrate-treated water at concentrations of two, four, and six 105-mL cups per tank.

In both experiments, C. rendalli and O. shiranus were stocked at a 1:2 male-to-female ratio. Nest and bower dimensions (length and width) were measured using a ruler, and mean diameters were calculated. Data were analyzed using two-way ANOVA in R (version 4.4.2) with the AgroR package, followed by Tukey's HSD test for post-hoc comparisons at $P < 0.05$ .

Key Contributions and Results
The study provides empirical evidence that both visual and chemical cues significantly influence reproductive structure construction, with significant interactive effects observed between the type of cue and the fish species ( $P = 0.002$ for visual; $P = 0.001$ for chemical).

Visual Cues: The largest structures were constructed when males and females were housed in the same tank but separated by a fine mosquito net. Under this condition, C. rendalli produced a mean nest diameter of $31.69 \pm 2.72$ mm, while O. shiranus produced a mean bower diameter of $23.01 \pm 0.72$ mm. The study found that C. rendalli is more sensitive to visual cues than O. shiranus, constructing significantly larger nests across all visual treatments. Notably, males built structures regardless of the substrate's proximity to the female, indicating that visual presence alone is a sufficient stimulus.
Chemical Cues: The addition of soil-substrate-treated water significantly increased the size of the constructed structures. The optimal concentration was identified as four cups of soil-substrate-treated water, yielding mean diameters of $28.52 \pm 1.16$ mm for C. rendalli and $26.17 \pm 1.16$ mm for O. shiranus. Both species showed reduced construction sizes at the highest concentration (six cups), suggesting that excessive chemical cues may inhibit or negatively affect the behavior. C. rendalli demonstrated a stronger response to chemical cues compared to O. shiranus.

Significance and Claims
The paper claims that these findings offer practical insights for improving hatchery breeding conditions for tilapia species. The authors assert that:

Visual stimulation is a primary driver for nest and bower initiation, with the "separated but visible" configuration proving most effective for maximizing structure size.
Chemical stimulation via soil-substrate water acts as a potent inducer for building behavior, but requires precise concentration management to avoid diminishing returns.
Species-specific differences exist in sensitivity to these cues, necessitating tailored management strategies; C. rendalli is generally more responsive to both cue types than O. shiranus.

The study concludes that providing substrates and manipulating the breeding environment with specific visual and chemical cues can mimic natural pre-spawning behaviors, thereby enhancing breeding success in captive settings. The authors recommend further research to determine if these cue-based mechanisms apply to other fish species.

1. The "See-You-There" Test (Visual Cues)

2. The "Scent of Home" Test (Chemical Cues)

3. Where Do They Build?

Why Does This Matter?

Technical Summary: Influence of Visual and Chemical Cues on Nest and Bower-Building Behaviours of Coptodon rendalli and Oreochromis shiranus

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