Background Information

Rivulus marmoratus (R. mar ) is the scientific name for the Mangrove Rivulus. Rivulus is the largest species of killfish. Mangrove Rivulus are in the Rivulidae family. Mangrove Rivulus is the only Rivulus species that live in North America.

Mangrove Rivulus live in the subtropics and tropical climates. The range of R. mar is southeastern Brazil to as far up as the Melbourne Beach in Florida (relative location: Melbourne, Florida). R. mar has the largest range of 70 other Rivulus.

Not much information is collected on its basic biology of Rivulus. Rivulus lives in burrows formed by land crabs (Cardiosmoa ). They are hermaphrodites that can fertilize themselves. They fertilize their eggs internally. No one is sure why but they can turn completely male. Males have been found in Florida but they are most common in the Central America and West Indies. Only two species of fish who are mangrove dependent (Gambusia rhizophorae is the other species besides R. mar) .

Females have a marbled brownish body and head with small dark spots. A large ocellus is located at the upper base of the rounded caudal fin. Males have an orange/pink body and head with small dark spots also. Males lack an ocellus yet are rarely found. The dorsal fin is distinctly posterior to the anal fin. The caudal fin is rounded The maximum size is about 20-40 mm in length. The longest R. mar found in Florida was 62 mm. R. mar that live in laboratories grow about that size in usually about two to three years old.

Scientists often note in their studies that R. mar can tolerate adverse water quality conditions. R. mar have been collected in salinity ranging from 0-68 ppt (parts per thousand) (Taylor et al., 1995). In studies juveniles remained viable at 70- 80 ppt (unpublished data). R. mar will reproduce at a lower salinity, but they will mature slower and grow at a larger size (Lin and Dunson, 1995). It has been unsuccessful to introduce R. mar to freshwater (Taylor, 1999a).

Rivulus are mostly carnivores who feed on cope pods, polychaets, fish scales, insects, and vegetable matter.

To catch Rivulus you take a piece of fishing line and put a small hook on it (preferably a brim hook) and tie a stick to the other end. Then you put on a small piece of shrimp, beetle, or worm and dangle the fishing line and hook in a crab burrow. Shake of “jig” the bait over the whole and the fish will be attracted to the motion. The Rivulus wont bite the hook, but it will hang onto the bait. Pulling up the hook slowly the fish can be grabbed or caught in a net (Taylor 1988). Other ways in catching Rivulus are traps (but not minnow traps). They can be left there until a tidal cycle occurs. Rivulus are usually found and collected in high salt water habitats and mangrove habitats.

R. mar was first discovered in the United State by Harrington and Rivas from the south of Florida in 1958. It has been collected from mangrove and mosquito ditch habitats (Hastings, 1975; Loftus and Kushlan, 1987).

Rivulus marmoratus was once generally thought that to was a synchronously hermaphroditic and self-fertilizing. In other words R. mar “clones” itself. An adult R. mar can produce up to 8 fertile eggs/day but on average it is about one egg/day.

The age of sexual maturity is often around 120 days. Specimens young as 90 days (this is from hatching) can sometimes oviposit.