Breeding Report: Megalamphodus bentosi (Bentosi Tetra)
The Bentosi Tetra (Megalamphodus bentosi), also known as the Rosy Tetra, is a beautiful and relatively hardy species that adds both color and life to the aquarium. Breeding this fish is achievable for dedicated aquarists with attention to water conditions, feeding, and timing. This report shares my experiences breeding this species over several attempts, highlighting both the challenges and successes.
Broodfish Selection and Conditioning
The broodfish used for breeding Megalamphodus bentosi were initially purchased as an impulse buy, chosen for their good size and vibrant appearance. These fish had been in my care for several months before I made the first attempt at breeding. This gave them ample time to settle into their environment and allowed me to observe their behavior and condition them properly.
Conditioning the broodstock was a key factor in achieving successful spawns. I focused on providing a rich and varied diet to bring the fish into prime breeding condition. This included:
- Frozen small bloodworms, a high-protein staple to stimulate spawning readiness.
- Frozen Artemia (brine shrimp), for essential fats and nutrients.
- Frozen cyclops and daphnia, to add variety and ensure a balanced diet.
- Baby brine shrimp (BBS), offered once or twice daily in small portions, as a fresh and highly nutritious supplement.
This feeding regime encouraged strong, healthy fish with well-developed gonads, capable of producing viable eggs and milt. I ensured the fish were well-fed but not overfed, as excess food and waste can compromise water quality and fish health.
Another important aspect of conditioning was timing breeding attempts with natural environmental cues. Based on reports from other breeders (such as on Chase Klinesteker’s web pages) and my own observations, I found that falling air pressure, such as before a thunderstorm, was a strong trigger for spawning. Monitoring the weather forecast became part of my preparation routine to increase the chances of a successful spawn.
The broodfish were kept together in a community tank between breeding attempts. Males and females remained in good health and displayed no significant aggression toward one another outside the spawning context. When spawning was planned, I selected the pairs or small groups to transfer to the breeding tank, choosing the fish that were in the best visible condition and most active in courtship displays.
In later attempts, I switched from using a single pair to two pairs in the breeding tank. This adjustment improved fertilization rates, likely compensating for a favored male who may have been aging and less fertile.
Water Parameters
The water composition was primarily reverse osmosis (RO) water with just a small addition of treated tap water, this is essential in my region, as the local tap water is extremely hard due to the underlying chalk aquifer. My target parameters were:
- pH: 6.5
- TDS: 20
- Temperature: 27.5–28°C
Interestingly, although conventional wisdom suggests highly acidic water is needed to trigger spawning in tetras, I found that my Megalamphodus bentosi bred successfully at these levels. What seemed far more critical was timing the attempt with falling air pressure or thundery weather, which consistently motivated the fish to spawn.
Physical Setup
The tank was designed for both the protection of eggs and the comfort of the breeding fish:
- Spawning substrate: A mesh grid (commonly called “oven chip” or French fry mesh) covered the tank bottom. This prevented the adults from eating their own eggs.
- Spawning media: Green synthetic yarn mops provided surfaces for egg deposition.
- Leaf litter: A large folded cattappa (Indian almond) leaf was placed near the heater. This added tannins, mimicked natural leaf litter, and offered additional hiding spots.
Filtration and Water Movement
Filtration was provided by a Xinyou XY-168 biochemical sponge filter, which was fully mature before being placed in the tank. The airflow was turned down very low, creating only gentle water movement. This helped:
- Prevent the formation of slicks on the water’s surface.
- Keep micro-life (such as paramecium) in suspension where fry could access it.
- Offer a safe refuge for fry under the sponge when they began free swimming.
Light and Disturbance Management
The breeding tank was kept in darkness throughout spawning and early fry rearing. This reduces stress, prevents fungus growth on the eggs, and mirrors natural conditions. To minimize disturbance in my fish shed (which also serves as my office), I screened the tank front with translucent white cellular foam packaging material. This simple barrier stopped external movement from spooking the fish during their delicate courtship and spawning activities.
Preparation for Spawning
The breeding tank was set up and stabilized ahead of a predicted change in weather, as falling air pressure is a strong spawning trigger. Broodfish were introduced mid-afternoon, and spawning typically began within 24 to 28 hours.
Once spawning had ceased, I removed the spawning media, mesh grid, and adult fish. The tank was then left dark and undisturbed as the eggs developed and hatched.
Spawning Behaviour
The courtship and spawning behaviour of Hyphessobrycon bentosi is both subtle and fascinating to observe. Recognising these signs can help aquarists predict when spawning is imminent and ensure the best chance of success.
Courtship Displays
In the days leading up to spawning, particularly in the community tank, I often noticed territorial posturing, especially from the males. Males displayed the classic tetra courtship behaviour:
- The dorsal, anal, and caudal fins were held fully erect, showing off their shape and colour.
- Males performed shimmering flanking movements, positioning themselves side-on to females and rivals.
- Occasionally, females themselves engaged in low-level posturing towards one another.
Once transferred to the breeding tank, these behaviours intensified. Courtship involved the male chasing the female among the spawning media, with both fish weaving through the yarn mops and around the leaf litter.
To reduce external disturbance and encourage natural behaviour, I screened the tank front with a piece of translucent white cellular foam (repurposed packaging material). This simple measure helped the fish focus on spawning without reacting to movement in the fish shed, which also serves as my workspace.
Spawning Timing and Triggers
I timed spawning attempts to coincide with falling air pressure or approaching thundery weather, which reliably encouraged the fish to spawn. Broodfish were typically introduced to the breeding tank in the mid-afternoon. Spawning would usually begin within 24 to 28 hours, depending on conditions.
Once spawning commenced, the eggs were scattered among the yarn mops or fell through the mesh grid to the tank bottom. The adults made no effort to guard the eggs; in fact, they would eat them if given the chance, hence the importance of the mesh and mops.
Post-Spawning Routine
After spawning had clearly finished, I removed the spawning media (mesh grid and mops) and netted out the adults. The adults were then carefully re-acclimatised to community tank water conditions before being returned to their usual home. The breeding tank was left dark and undisturbed to protect the eggs and allow them to develop.
In cases of large spawning events, whether with Megalamphodus bentosi or other large tetras like Red Eye or Black Widow, I sometimes performed a 30–40% post-spawn water change, replacing the removed water with straight RO water at the same temperature. This helped dilute any protein build-up from spawning activity and maintained water quality. A small sponge filter on gentle flow continued to provide minimal filtration without disturbing the eggs.
Hatching
Egg development time varied slightly with temperature:
- At around 27.5–28°C, eggs typically hatched within 18 to 22 hours.
- At cooler temperatures (around 25°C), hatching took closer to 26 hours.
Once hatched, larvae clung to tank surfaces for a day or so before becoming free-swimming and ready for first foods.
Raising the Fry
Successfully raising Hyphessobrycon bentosi fry requires a careful balance of food availability, water quality, and minimal disturbance. Over several spawning attempts, I’ve developed a routine that reliably produces healthy juveniles.
First Foods and Feeding Routine
Once the fry became free-swimming, typically a day or so after hatching, feeding began immediately. However, it’s important to note that larvae usually start sustained pelagic swimming and first feeding between 3.5 and 4.5 days after the eggs were laid. This stage marks the transition from clinging to tank surfaces to actively searching the water column for food.
The goal at this point is to ensure that a constant supply of microscopic food is already present in the water, so the fry can begin feeding as soon as they are ready.
Preferred Approach: Paramecium and Microfoods
My preferred method is to start with paramecium cultures, as they are small enough for even the tiniest fry to consume. Paramecium provides a uniform, reliable first food that encourages even early growth. I usually begin adding small amounts of paramecium as soon as I see fry clinging to the tank walls or hanging under the sponge filter, heater, or folded cattappa leaf. Having food in the tank prior to the fry’s first feeding attempts is, in my experience, essential for a strong start.
Alongside paramecium, I add small quantities of:
- Golden Pearl fry powder (smallest grade), mixed into a suspension and dosed sparingly.
- Microworms, used primarily to introduce subtle movement in the water column, which helps stimulate the fry’s feeding response.
Alternative Approach: Liquifry and Dirty Tank Microfauna
When paramecium cultures aren’t available, I rely on Interpet Liquifry for egg layers, which helps promote infusoria growth directly in the tank. It’s crucial to dose the tank with Liquifry before the fry reach the point of first feeding. I simply follow the instructions on the Liquifry bottle, ensuring the water contains sufficient suspended food and micro-life by the time the fry begin to actively search for nourishment.
In these cases, fry also benefit from the microfauna present in a well-seasoned, so-called “dirty tank”, containing a mature sponge filter, cattappa leaf, and natural biofilm.
Introducing Brine Shrimp
After about 1.5 to 2 days of initial microfood feeding, I begin introducing San Francisco Bay strain baby brine shrimp (BBS). I dribble the BBS in small amounts using a pipette, often mixed with a little tap water to help gradually increase hardness. Using a flashlight to check for orange bellies helps confirm that the fry are taking the shrimp. Early introduction of BBS encourages rapid growth and helps the fry transition from microscopic foods to more substantial prey.
Key Takeaway
Regardless of the method, the critical point is to have food available before the fry’s first feeding stage, rather than waiting until they are actively swimming in the water column. This ensures they have immediate access to nutrition and supports healthy, even development from the start.
Cleaning and Water Changes
The 12-litre breeding tank is typically filled with 8 to 9 litres of water at the start. After spawning, I immediately draw off some water and replace it with fresh RO water to dilute the proteins released during spawning, which helps maintain water quality and reduce the risk of egg or fry losses.
To ensure the majority of fry successfully inflate their swim bladders at the surface, I aim to keep the water depth below 15 centimeters during the earliest stages. This shallow depth supports the fry’s natural behaviour and development.
In the early days of cleaning and refilling:
- I start by removing about 1 litre of water and replacing it with around 1.5 litres of warmed RO water.
- As the fry grow, I gradually increase this to removing 1 litre and replacing with 2 litres, slowly building up the tank’s water volume.
Once the fry are about a month old and showing more adult characteristics, I begin to increase water hardness. This is done by replacing water during cleaning with a mix of RO and treated tap water. Additionally, a slight increase in hardness occurs naturally, as I feed BBS that has been rinsed and pipetted using a small amount of tap water.
This gradual, careful management of water quality and composition supports healthy growth and reduces stress on the developing fry.
Growth and Transfer
Growth is rapid once the fry are established on BBS, with feeding increased to 2–3 times per day as they grow. On average, I see about 120 fry survive to the juvenile stage per batch.
As the fry outgrow the breeding tank, they are moved into progressively larger tanks, with the largest grow-out tank in my setup being 64 litres. By 2.5 to 3 months, the young fish are sub-adult size and beginning to show sexual dimorphism.
Key Considerations
- Filter placement: I raise the sponge filter so that it sits just below the water surface. This reduces circulation, helping to keep paramecium and early foods in suspension for easy access by the fry.
- Lighting: The tank remains dark during these early stages to reduce stress and discourage fungus growth.
- Feeding transition: The key is to balance early microfoods with timely introduction of BBS, gradually reducing reliance on liquids, powders, and paramecium over the first week.
In batches with larger spawns or heavy feeding, I sometimes perform a 30 to 40% water change after spawning to reduce protein build-up, using straight RO water to maintain clean conditions.
Reflections and Advice
Breeding Hyphessobrycon bentosi has proven to be both rewarding and relatively straightforward, provided a few key principles are followed. Through several attempts, I’ve found that success comes down to preparation, observation, and timing rather than obsessing over perfect water chemistry.
Spawning Triggers
While many sources suggest that H. bentosi requires very soft, acidic water to spawn, my experience has shown that falling air pressure and changes in weather, particularly approaching thundery conditions, are far more important triggers. Careful timing of breeding attempts around these natural cues greatly increases the chance of success.
Water Parameters and Setup
Although I maintained water at pH 6.5 and low TDS (~20), the fish were willing to spawn at these levels without needing to push to extreme acidity. A well-prepared tank with aged filtration, spawning media, and minimal disturbance matters far more than chasing exact numbers.
Managing Early Spawns and Challenges
One challenge for newcomers is coping with batches where most eggs turn white and fungus over, especially on first attempts. This can be disheartening, but it’s common, females can become spawn-bound, producing poor-quality eggs if they haven’t spawned in a while. The key is patience:
- Allow the female to shed old eggs.
- Recondition her with high-quality live and frozen foods.
- Try again after two weeks, success usually follows.
Fry Rearing Success
Once the fry begin feeding, I find that good numbers, on average around 120 juveniles per batch, can be raised. Even without access to paramecium, using Liquifry, microworms, and seasoned tank setups produces respectable results, though initial growth may be slightly slower. The critical factor is introducing BBS early (after about 1.5 to 2 days of initial feeding) and gradually transitioning from microfoods.
Maintaining cleanliness with gentle, daily water changes and careful feeding prevents most common problems like belly sliders or stunted growth.
Final Advice for Hobbyists
- Don’t overcomplicate things. Focus on conditioning your fish, timing your spawn with weather patterns, and keeping the breeding setup clean and simple.
- Don’t be discouraged by early failures. Spawning quality improves with the experience of both the aquarist and the broodstock.
- Adapt and observe. Small adjustments, like using two pairs instead of one or screening the tank to reduce disturbance, can make a significant difference.
- Enjoy the process. Breeding H. bentosi is a great learning opportunity that will improve your skills for other species as well.
With preparation, patience, and a little help from the weather, you can successfully breed this beautiful tetra and enjoy watching a new generation grow.
Summary video
Author
Mike Lee
Copyright foto’s and video
Mike Lee
Post-processing
John de Lange
