The green swordtail or Xipho (Xiphophorus hellerii) is a vibrant and popular species in the world of freshwater aquariums. This hardy fish, with its distinctive sword-like tail extension, has captivated enthusiasts for decades.
The green swordtail is also a common animal in research laboratories, where it is used as a model organism for studies on female preferences and male conflicts, as well as for melanoma research (Schartl and Lu, 20244).
In this article, we will delve into everything you need to know about green swordtails, ensuring that you can provide the best environment and care for these colorful companions.
What do green swordtail fish look like?
Physical characteristics
Green swordtails are small fish characterized, in the case of males, by a caudal fin whose lower rays extend backward, resembling a “sword.”
According to Rosenthal and Evans (1998), green swordtails are a paradigmatic case of sexual selection through sensory exploitation, due to the female green swordtail’s preference for males with larger “swords,” suggesting that the morphology of male green swordtails has evolved in response to this bias.
Male Xiphos average 8 to 11.3 cm in length as adults, though individuals of up to 14 cm have been recorded; on the other hand, female green swordtails are larger and can reach up to 16 cm.
In their natural habitat, wild Xiphos exhibit a greenish color with a yellow-green stripe running along the length of their body. However, due to extensive breeding in captivity, green swordtails can now be found in orange, black, and red colors.
Xiphos can reach an age of 5 years in their natural habitat; however, in captivity (aquariums) and with proper care, they can live up to 6 years.
Hybrid varieties
Over the years, selective breeding has led to various color forms and hybrids of the green swordtail, including red, albino, and lyretail varieties. These hybrids may offer unique appearances but generally require the same care as the standard green swordtail.
Taxonomy of the Green Swordtail
The green swordtail, also known as Xipho or Xifo, has the following taxonomy:
- Phylum: Chordata
- Class: Actinopterygii
- Order: Cyprinodontiformes
- Family: Poeciliidae
- Genus: Xiphophorus
- Species: Xiphophorus hellerii (Heckel, 1848)
- Common name in Spanish: pez cola de espada, pez xifo or Xipho, pez espada verde
- Common name in English: Green Swordtail, Swordtail
Etymology: Xiphophorus: Greek, xiphos = sword + Greek, pherein = to bear
The green swordtail belongs to the family Poeciliidae and is closely related to guppies, mollies, and platies. The green swordtail gets its name from the elongated lower lobe of the male’s caudal fin, which resembles a sword. This characteristic not only distinguishes them visually but also plays a role in mating displays and interactions.
Habitat of Green Swordtails
The green swordtail is native to Central America, with abundant natural populations in Mexico, Honduras, Belize, and Guatemala. However, X. hellerii has been introduced in the U.S., Canada, Puerto Rico, Africa, Sri Lanka, Australia, Guam, Fiji (Tamaru et al., 2001), Iran, and Morocco.
Green swordtails thrive in rivers, streams, and ponds with slow-moving waters, dense vegetation, and a mix of open swimming spaces.
Rocamontes et al (2021) found that the body shape of green swordtails varies between basins and hydrological regions, and that temperature appears to affect body shape. The researchers conclude that Xipho fish from different basins and hydrological regions have followed independent evolutionary paths.
Care of Swordtails fish in an Aquarium
The following are the basic parameters for keeping green swordtails in an aquarium:
Table 01. Water quality parameters for breeding green swordtails.
| Parameter | Range |
| Aquarium Volume | Minimum 100 liters |
| Water Temperature | 20 a 26 °C |
| Water pH | 7.0 to 8.3 |
| Dissolved Oxygen | > 2.0 ppm |
| Total Ammonia | < 1.0 ppm |
| Hardness | 15 to 30 dGH |
In addition, the tanks should include:
- Substrate: A sandy or fine gravel substrate mimics their natural riverbed environment.
- Plants: Dense vegetation, including live plants like Java moss, Vallisneria, and Anubias, provides hiding spots and mimics their natural habitat. Floating plants can also help diffuse light and create shaded areas.
What do green swordtails eat?
Green swordtails are omnivores and accept all types of flake food as well as live food (water fleas, brine shrimp, mosquito larvae, tubifex, etc.).
Green swordtails need a varied diet to stay healthy and vibrant. A balanced diet should include:
- Flakes and pellets: High-quality flakes or pellets formulated for tropical fish provide essential nutrients.
- Live and frozen foods: Complement their diet with live or frozen foods such as brine shrimp, daphnia, and bloodworms. These foods enhance their coloration and mimic their natural feeding habits.
- Vegetables: Occasionally offer blanched vegetables like spinach, zucchini, and peas to provide fiber and variety.
Feed them 1 or 2 times a day, offering only what they can consume in a few minutes to avoid overfeeding and water quality issues.
Studies on Green Swordtail Nutrition
Color Enhancement
Researchers such as James et al. (2006) recommend incorporating up to 8% spirulina into the green swordtail’s diet to maximize growth, reproduction, and especially coloration. Rashidian et al. (2020) suggest feeding X. hellerii breeders with a dose of 100 mg/kg astaxanthin for better growth and reproductive performance; while Al Bari (2020) concluded that the natural carotenoids from marigold (Tagetes erecta) have positive effects on the body coloration of green swordtails.
Breeder Feeding
The protein requirement for female green swordtails during reproduction is crucial for somatic growth and optimizing fry production. Chong et al. (2004) recommend including at least 30% protein in the females’ diet. Sharma and Garg (2023) found that maximum fry production was achieved with a food application containing 3% earthworm meal (Eisenia fetida) in Xiphophorus helleri.
Additionally, Beiranvand et al. (2020) recommend a daily feeding rate of 3% of the breeders’ body weight to achieve the highest number of larvae.
Juvenile Feeding
For feeding juvenile green swordtails, Debnath et al. (2022) determined that a custard mix (blue cornflower, agar powder, milk powder, egg, cod liver oil, and shrimp meat) could be a potential food source for X. hellerii juveniles in terms of availability, cost, ecological, and health risk considerations.
How to Breed Green Swordtails
Breeding green swordtails is relatively easy, making them a popular choice for aquarists. These viviparous fish give birth to free-swimming fry instead of laying eggs and, under suitable conditions, can reproduce frequently.
Green swordtails exhibit sexual dimorphism, with males having a “sword” on their dorsal fin, which females lack. Xiphophorus hellerii reaches sexual maturity at 10-12 weeks of age, is ovoviviparous, and its reproduction is straightforward. The optimal breeding temperature is between 22 and 26 °C.
Once sexually mature, Xipho do not form pairs and are completely polygamous. Males court not only females of their own species but also females of other poeciliids, leading to hybridization (Tamaru et al., 2001).
The male green swordtail “courts” the females, and through the gonopodium, introduces sperm into the female to fertilize the eggs. A ratio of 1 male to 3 females is recommended to reduce female stress, as males can be persistent during courtship.
Gestation and Embryonic Development
The female green swordtail can store viable sperm in her oviduct to fertilize mature eggs as needed. A single mating can provide viable sperm for fertilization for up to two years.
The female green swordtail fertilizes the eggs with the male’s sperm, and pregnancy can last from 4 to 6 weeks. Each female can give birth to 20 to 100 live fry, depending on the size of the mother.
You should separate the fry into a breeding aquarium or tank once they are born, as the parents might eat them.
Breeding Recommendations
It is important to note that in some cases, female swordtails may develop male characteristics, which is quite common in this species.
Optimal fry production is achieved from breeders that are 6 to 12 months old or between 63.5 – 76.2 mm in size.
Fry production decreases once breeders reach one year of age, as evidenced by a decrease in the number of fry per female per day.
Fry should be fed with finely crushed flakes, brine shrimp nauplii, or special fry food.
Diseases Affecting Swordtail Fish
Like all aquarium fish, green swordtails are susceptible to certain diseases, often resulting from poor water conditions or stress. Common health issues include:
- Swim Bladder Disease: A condition affecting buoyancy, often caused by poor diet or infection.
- Ich (White Spot Disease): A parasitic infection that causes white spots on the body and fins.
- Fin Rot: A bacterial infection that leads to the deterioration of fins.
Bacterial Diseases
Aeromonas bacteria are pathogens affecting a wide range of fish species. Das et al. (2020) reported that Aeromonas veronii infections in X. hellerii can be treated using a zinc oxide nanoparticle bath (1 mg/L).
Parasites
Tamaru et al. (2001) reported that the three most problematic diseases in commercial swordtail farming are protozoan infections (Trichodina), monogeneans (Dactylogyrus and Gyrodactylidae), and fungi (Saprolegnia).
The use of non-iodized salt, at a concentration between 25 and 35 g/L, can be employed to treat protozoa and monogeneans. Specialists recommend conducting preliminary tests on small samples of fish to determine the most appropriate time and concentration.
Swordtail Compatibility
In general, swordtails are peaceful and tend to ignore other fish, although males tend to be very territorial. If there are 2 or more males in the group, one is likely to become a dominant male.
Experts recommend one male for every three or four females.
In the wild, swordtails live alongside platies. However, in aquariums, compatible fish with swordtails include mollies, guppies, platies, neon tetras, zebras, and other ornamental fish species.
Conclusion
The green swordtail fish is resilient and visually striking, making it a pleasure to keep in both beginner and experienced aquariums. With proper attention to its habitat, diet, breeding, and general care, these fish can thrive and bring vibrant life to your aquarium. Remember to monitor water quality, provide a balanced diet, and consider their breeding habits to ensure a healthy and active population of green swordtails in your tank.
In summary, swordtails are an excellent choice for aquarists seeking a dynamic and colorful species. With the right care and environment, these fish can thrive, providing both aesthetic pleasure and the satisfaction of observing their natural behaviors and interactions.
References
Al Bari, A. (2020). EFFECTS OF NATURAL CAROTENOIDS ON THE BODY COLORATION OF SWORD TAIL FISH (Xiphophorus hellerii) (Doctoral dissertation, Chattogram Veterinary and Animal Sciences University Chattogram-4225, Bangladesh).
Beiranvand, N., Dadgar, S., & Mazandarani, M. (2020). Effect of different feeding rate on reproductive performance of Swordtail (Xiphophorus helleri). Journal of Aquaculture Development, 14(1), 1-13.
Chong A., Saraitul Dahlianis Ishak, Zulfaizuddin Osman, Roshada Hashim. 2004. Effect of dietary protein level on the reproductive performance of female swordtails Xiphophorus helleri (Poeciliidae). Aquaculture, Volume 234, Issues 1–4, 3 May 2004, Pages 381-392 https://doi.org/10.1016/j.aquaculture.2003.12.003
Das, S., Aswani, R., Midhun, S. J., Radhakrishnan, E., & Mathew, J. (2020). Advantage of zinc oxide nanoparticles over silver nanoparticles for the management of Aeromonas veronii infection in Xiphophorus hellerii. Microbial Pathogenesis, 147, 104348. https://doi.org/10.1016/j.micpath.2020.104348
Debnath S, Sarker DS, Kundu P, Parvez MS, Arafat ST, Mathew RT, Alkhamis YA, Rahman MM, Rahman SM (2022). Growth, survival and body protein content of swordtail (Xiphophorus helleri) fed live and formulated feeds. Adv. Anim. Vet. Sci. 10(2): 335-341. http://dx.doi.org/10.17582/journal.aavs/2022/10.2.335.341
James R., K. Sampath, R. Thangarathinam, I. Vasudevan. 2006. Effect of dietary spirulina level on growth, fertility, coloration and leucocyte count in red swordtail, Xiphophorus helleri. The Israeli Journal of Aquaculture – Bamidgeh 58(2), 2006, 97-104
Rashidian Ghasem, Simona Rainis, Marko D. Prokić & Caterina Faggio (2021) Effects of different levels of carotenoids and light sources on swordtail fish (Xiphophorus helleri) growth, survival rate and reproductive parameters, Natural Product Research, 35:21, 3675-3686, DOI: 10.1080/14786419.2020.1723091
Rocamontes-Morales, J.A., Gutiérrez-Rodríguez, C., Rios-Cardenas, O. et al. Genetic and morphological differentiation in the green swordtail fish, Xiphophorus hellerii: the influence of geographic and environmental factors. Hydrobiologia 848, 4599–4622 (2021). https://doi.org/10.1007/s10750-021-04664-0
Rosenthal G. and Christopher S. Evans. 1998. Female preference for swords in Xiphophorus helleri reflects a bias for large apparent size. BIOLOGICAL SCIENCES, 95 (8) 4431-4436 | https://doi.org/10.1073/pnas.95.8.4431
Sharma, K., Garg, V.K. Utilization of vermi-incorporated feed for the seed production of two freshwater ornamental fish, Xiphophorus helleri and Poecilia sphenops. Biomass Conv. Bioref. (2023). https://doi.org/10.1007/s13399-023-04955-7
Schartl Manfred , Yuan Lu; Validity of Xiphophorus fish as models for human disease. Dis Model Mech 1 January 2024; 17 (1): dmm050382. doi: https://doi.org/10.1242/dmm.050382
Tamaru Clyde, Brian Cole, Rich Bailey, Christopher Brown, and Harry Ako. 2001. A Manual for Commercial Production of the Swordtail, Xiphophorus helleri. University of Hawaii Sea Grant Extension Service. CTSA Publication Number 128. 38 p.
