The Black Widow Tetra, also known as the Black Tetra or Gymnocorymbus ternetzi, is a small, freshwater fish that is native to South America. It is a popular fish for aquariums due to its peaceful nature, hardiness, and striking coloration.
The Black Tetra has become increasingly popular among aquarium hobbyists due to its attractive appearance and ease of breeding. The development of fluorescent red neon tetras (Pan et al., 2008), also known as transgenic neon tetras or GloFish, further increased its popularity.
This tropical freshwater fish is native to South America. Black Widow Tetra are small and colorful, making them popular among aquarium enthusiasts for their peaceful nature and easy care. They can be found in many pet and aquarium stores and are an ideal choice for beginners in the aquarium hobby.
This article provides information on the care, breeding, and characteristics of Black Tetras for aquarium enthusiasts.
Characteristics of Black Widow Tetra
Taxonomy
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Subclass: Neopterygii
- Infraclass: Teleostei
- Superorder: Ostariophysi
- Order: Characiformes
- Family: Characidae
- Genus: Gymnocorymbus
- Scientific name: Gymnocorymbus ternetzi
- English name: Black Widow Tetra, Black Tetra, Petticoat tetra, and blackamoor.
Anatomy and Morphology
In the wild, Black Widow Tetras can grow up to 7.5 cm in length, but in aquariums, they can reach a size between 4 and 6 cm. Males are smaller than females. In captivity, these fish can live up to 5 years.
The main difference between male and female Black Widow Tetras is that the male has a wider anal fin and a more pointed dorsal fin than the female.
Contrary to their name, there are varieties of different colors of Black Tetras. According to Frankel (2004), wild Black Widow Tetras exhibit two phenotypes associated with body bands:
- Black Tetra: smoky gray coloration with two prominent black vertical bands located directly behind the operculum.
- White skirt tetra: lighter coloration and lack of vertical bands.
Naturally occurring color variations of Black Tetras can range from white to pink; however, aquarists have developed different color lines, as well as long-finned varieties (Sharpe, 2020).
Natural Habitat
Black Widow Tetras are native to the Paraguay River and Amazon River basins, but wild populations are also found in Brazil, Peru, Argentina, and Bolivia.
The distribution of Gymnocorymbus ternetzi has expanded to many continents thanks to the aquarium industry. In some countries, they are considered invasive species due to their release into the natural environment.
Diet
Black Tetras are omnivores in their natural environment, eating worms, small crustaceans, and insects. When raised in aquariums, they will accept all types of fish food (live, fresh, frozen, flake).
However, it is important to note that Kuhn et al. (2023) reported that increasing water temperature affects the feeding of Black Neon Tetras (Gymnocorymbus ternetzi).
Feeding Black Widow Tetra Fry:
- It is important to feed Black Neon Tetra fry with live food depending on the size of their mouth.
- Once the yolk sac is consumed, they should be fed first with infusoria and then with Artemia nauplii.
Feeding Behavior of Black Tetra Larvae:
Sarma et al. (2003) studied the feeding behavior of Black Widow Tetra larvae from hatching to 8 weeks and concluded the following:
- The rotifer Brachionus calyciflorus was attacked, captured, and ingested by Black Neon Tetra larvae from the first to the eighth week.
- Black Tetra larvae did not capture or ingest water fleas (Daphnia pulex and Moina macrocopa) until the fifth week.
- Black Widow Tetra larvae showed an increase in the consumption of Brachionus patulus with increasing larval age.
Lipscomb et al. (2020) recommend weaning Black Widow Tetra fry from Artemia to microparticle diets 12 days after hatching, as this has been shown to improve survival.
If you are using artificial feed to feed your Black Tetras, adding vitamin C to the food at a rate of 50 mg/kg of food is the best dose for growth, survival, feed efficiency, FCR, and stress test (Dhewantara et al., 2023).
Reproduction
Black Widow Tetras are oviparous, highly prolific, and relatively easy to breed. An important characteristic is that juveniles of Gymnocorymbus ternetzi are hermaphrodites, and then a sexual reversal process occurs. If you want to learn more about this aspect, I recommend that you review the study by Mazzoni et al. (2015).
Breeding Setup
To breed Gymnocorymbus ternetzi, you can use a 50-liter aquarium with abundant vegetation, low light, and a ratio of 2 male Black Widow Tetras for every female fish. The water temperature should be in the range of 27 to 29 °C, and you should include floating plants such as “foxtail” (Ceratophyllum sp.) to provide suitable conditions for the breeders.
During courtship, the male Black Widow Tetra swims with its fins spread in circles or zig-zags around the female until she lays between 300 and 400 eggs.
Hatching and Fry Development
According to Çelik et al. (2012), hatching occurs 20-21 hours after spawning at an average temperature of 24 °C. The mouth of the Gymnocorymbus ternetzi fry opens 3 days after hatching, when the yolk sac is completely absorbed and they begin to swim actively. The researchers also found that the Black Tetra fry completed metamorphosis and transformed into juveniles 32 days after hatching.
Egg Care
An important aspect during reproduction is the care of the fertilized eggs. In this regard, Chambel et al. (2014) determined that the optimal doses of the chemicals used in the disinfection of the eggs of the G. ternetzi, to increase hatching, were 1 mg/L for the iodine solution, 25 mg/L for hydrogen peroxide, and 3 mg/L for methylene blue.
Triploidization
If you are interested in producing Black Widow Tetras for sale, the use of triploidization techniques will allow you to obtain fish that grow faster. Uma and Chandran (2008) successfully induced triploidy by heat shock in the Black Tetra, Gymnocorymbus ternetzi.
Black Widow Tetra Care and Breeding Conditions
Black Tetras are not very demanding and can be bred in aquariums as small as 50 liters. Steven et al. (2006) found that group size did not affect the growth rate of Gymnocorymbus ternetzi when raised in groups of 16 individuals in a 50-liter tank. However, larger aquariums are recommended so that they can swim comfortably.
The aquarium decoration should include abundant plants (planted aquarium). Gymnocorymbus ternetzi loves plants because they can explore and swim through them. Black Tetras will stand out much more if the substrate is dark in color.
Table 1. Black Widow Tetra Aquarium Breeding Parameters
| Parameter | Ideal Value |
|---|---|
| Fish tank volume | 80 to 120 liters. |
| Temperature | 20-28 °C (79-82 °F) |
| pH | 6.0-8.0 |
| Hardness | 3-10 dGH |
| Nitrates | < 50 mg/L |
| Lighting | Moderate |
| Filtration | Good |
| Water Changes | 25% – 30% weekly |
Black Tetra Behavior and Compatibility
Black Widow Tetras are schooling fish and live in groups of 8 to 10 individuals. They are ideal for community aquariums but should not be kept with long-finned fish (e.g., guppies or angelfish) because they will nip at their fins.
They tend to swim in the middle part of the aquarium. Ideal tankmates for Gymnocorymbus ternetzi include other tetras, barbs, mollies, and platies.
Diseases that Affect Gymnocorymbus ternetzi
- Ichthyophthirius multifiliis: This ciliated protozoan causes “Ich” or “White Spot Disease.” Aydogan et al. (2010) reported the natural infection of Gymnocorymbus ternetzi with Ich.
- Parasites: Acchile et al. (2017) reported that monogenean parasites such as Diaphorocleidus kabatai attach to the gills of Black Tetras. Malek et al. (2021) reported infestations of Tetrahymena sp. and Dactylogyrus sp. in GloFish tetras (Gymnocorymbus ternetzi) and recommended treatment with 37% salt and formalin baths.
Conclusion
Black Widow Tetras (Gymnocorymbus ternetzi) are ideal for beginners in the aquarium hobby. Their beauty and hardiness make them easy to breed and care for. They are a fascinating and easy-to-care-for aquarium fish, making them an ideal pet for beginners and experienced hobbyists alike. By following the tips in this article, you can provide your Black Tetras with a long and healthy life.
Fluorescent Black Tetras are gaining popularity due to their vibrant colors. However, there are concerns about the environmental impacts of their release into the wild.
References
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