Introduction:

Aplocheilichthys johnstoni, commonly known as Johnston’s killifish, is a captivating freshwater fish species that belongs to the family Aplocheilidae. This species is native to various parts of West Africa and is particularly well-known for its striking coloration and unique behaviors. In this article, we will delve into various aspects of Aplocheilichthys johnstoni, including its taxonomy, habitat, physical characteristics, behavior, reproduction, and its relevance in the aquarium hobby.

Taxonomy:

Aplocheilichthys johnstoni is classified under the following taxonomic hierarchy:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Actinopterygii (ray-finned fishes)
• Order: Cyprinodontiformes (toothcarps)
• Family: Aplocheilidae (killifishes)
• Genus: Aplocheilichthys
• Species: johnstoni

Habitat and Distribution:

Johnston’s killifish is predominantly found in West Africa, particularly in regions that have a tropical or subtropical climate. Its natural habitat includes various freshwater environments such as rivers, streams, ponds, swamps, and temporary pools. These habitats are typically characterized by slow-moving or stagnant water, abundant aquatic vegetation, and a variety of microorganisms and small invertebrates, which serve as a food source for these fish.

The distribution of Aplocheilichthys johnstoni spans several countries in West Africa, including Ghana, Ivory Coast, Liberia, and Sierra Leone. They are often associated with lowland areas and are frequently found in areas with seasonal rainfall and water bodies that experience fluctuations in water levels.

Physical Characteristics:

1. Size: Johnston’s killifish is a small species, with adult individuals typically reaching a size of 4 to 6 centimeters (1.5 to 2.5 inches) in length.
2. Coloration: One of the most striking features of this species is its vibrant coloration. Male Johnston’s killifish display a stunning combination of colors, including shades of blue, green, red, and yellow. Females, on the other hand, are generally less colorful and tend to be more subdued.
3. Fins: This species possesses prominent dorsal and anal fins, which may be adorned with intricate patterns and vibrant colors. These fins contribute to their overall visual appeal.
4. Body Shape: The body of Aplocheilichthys johnstoni is elongated and somewhat compressed laterally, allowing them to navigate through dense aquatic vegetation in their natural habitat with ease.

Behavior:

Johnston’s killifish exhibit a range of interesting behaviors that make them a captivating species to observe:

1. Territorial Behavior: Male Johnston’s killifish can be territorial, particularly during the breeding season. They establish and defend small territories within their habitat and may engage in territorial disputes with other males.
2. Courtship Displays: Male killifish are known for their elaborate courtship displays. During courtship, they often display vibrant colors and perform intricate fin displays to attract females.
3. Feeding Behavior: In their natural habitat, Johnston’s killifish are opportunistic feeders, primarily consuming small aquatic invertebrates and insects. In captivity, they readily accept a variety of live and frozen foods.
4. Solitary Nature: Outside of the breeding season, these killifish are generally solitary, and they do not form large shoals. However, they can be kept in small groups in aquariums with adequate space.

Reproduction:

The reproductive behavior of Aplocheilichthys johnstoni is a fascinating aspect of their biology. They are known for their annual killifish breeding strategy, which involves the following steps:

1. Courtship and Pair Formation: As the rainy season approaches, male Johnston’s killifish become more active and exhibit courtship behaviors, including vibrant color displays. Once a male successfully attracts a female, they form a pair.
2. Egg Deposition: The female lays her eggs in the substrate, typically in mud or leaf litter at the water’s edge. The eggs are adhesive and attach to the substrate.
3. Egg Survival: The eggs of Johnston’s killifish are highly resilient and can survive in the dry mud or leaf litter when the temporary breeding pools dry up. They enter a state of diapause or suspended animation, allowing them to survive until the next rainy season.
4. Hatching: When the rains return, the breeding pools fill with water, triggering the hatching of the eggs. The fry emerge and begin feeding on small aquatic invertebrates and microorganisms present in the water.
5. Growth and Development: The fry grow rapidly and reach maturity within a few months, at which point they are ready to reproduce in the following breeding season.

Aquarium Care:

Aplocheilichthys johnstoni is a popular choice among aquarium hobbyists due to its striking appearance and manageable size. Here are some essential care tips for keeping Johnston’s killifish in an aquarium:

1. Tank Size: Provide a tank with a minimum capacity of 10 gallons for a small group of these fish. A larger tank will accommodate more individuals and provide more swimming space.
2. Water Parameters: Maintain stable water conditions with a temperature range of 72-78°F (22-26°C), a pH level around 6.0-7.5, and soft to moderately hard water. Regular water changes are essential to keep water quality high.
3. Substrate: Use a substrate that mimics their natural habitat, such as fine gravel or sand. Adding dried leaves or Indian almond leaves can provide hiding spots and create a natural look.
4. Filtration: Use a gentle filtration system with a sponge filter or a low-flow power filter to prevent strong currents that might stress these fish.
5. Tankmates: Johnston’s killifish are generally peaceful but can become territorial during the breeding season. Keep them with other small, non-aggressive species, such as small tetras, rasboras, or peaceful bottom-dwellers.
6. Feeding: These fish readily accept live or frozen foods like daphnia, brine shrimp, and small insects. You can also provide high-quality flake or pellet foods, but live or frozen foods should be a significant part of their diet.
7. Breeding: To encourage breeding, provide suitable spawning substrates like spawning mops or fine-leaved plants. Maintain stable water conditions and a photoperiod that mimics the seasonal changes in their natural habitat.

Conclusion:

Aplocheilichthys johnstoni, or Johnston’s killifish, is a captivating species that offers both scientific interest and aesthetic appeal. Its unique annual breeding strategy, stunning colors, and manageable size make it a popular choice for aquarium enthusiasts. By understanding their natural behavior and providing a suitable environment, hobbyists can enjoy the beauty and wonder of these fascinating fish in their own homes. Responsible ownership and care are essential to ensuring the health and well-being of Johnston’s killifish in captivity, as with all aquarium species.