Western Mosquitofish Genus: Gambusia Species: G. affinis Maximum Size: 1.5” (males), 3” (females) Aggression: High Temperature: 65-74 F pH: 7-8.5 Hardness: 10-30 dH Brackish Tolerance: 1.000-1.025 Minimum Tank Size: 15 gallons Feeding: Flake foods accepted, does best on brine shrimp, Mysis shrimp, insect larvae
Notes: Mosquitofish are not commonly found in the aquarium trade, though are sometimes inadvertently sold in batches of wild-type and feeder guppies. Mosquitofish are remarkably adaptable and have been shown to tolerate temperatures up to 108 F and specific gravities up to twice sea water for short periods of time. Long term, they are best kept in cold-to-subtropical conditions with hard water. They are good candidates for outdoor ponds that are too small for groups of goldfish. In the home aquarium, they are extremely aggressive, nippy fish that often do not tolerate any other fish in their territory. Gobies, Hoplosternum catfish, and some of the more aggressive crabs like Red Clawed Crabs are possible tankmates, but may not be suitable long term. Species-only aquariums are better choices and even then multiple males will likely fight in any moderately sized tank. Like other fish in the Poecilidae family, they produce live young at regular intervals (about every 3-4 weeks). No special steps need to be taken by the aquarist to trigger spawning, but fry should be moved to another tank if wanted to be kept alive.
Campton, D. E.; Gall, G. A. E. (1988). “Growth and reproduction of the mosquitofish, Gambusia affinis, in relation to temperature and ration level: consequences for life history”. Environmental Biology of Fishes
Why does this fish’s penis resemble a medieval weapon?
“Biologists recently discovered a new species of freshwater fish called the llanos mosquitofish, or Gambusia quadruncus, in which the male members of the species have genitalia with four pronounced hooks on them, while the females feature a colorful anal spot. Now, it’s quite possible that these fish have some kind of S&M thing going on, but the scientists who are studying them believe they know what’s really going on — and it ain’t pretty.”
These little fishies were found in an anchialine pool in West Hawaiʻi. A species introduced to Hawaiʻi, G. affinis can have dramatic impacts on anchialine pool ecology. Although they can prey on the native shrimp ʻōpaeʻula (Halocaridina rubra), one of the most significant impacts they have is changing the behavior of the shrimp. Shrimp in the same pools as G. affinis switch to nocturnal behavior, coming out mostly at night to avoid predation by the visually-feeding fish. As a result, ʻōpaeʻula are less seen during the day and may forage less as a tradeoff for hiding.