Mangrove Killfish: Living on Land for 66 Days

Taking a look at the Mangrove Killfish will provide no clues into just how unique a creature it is. After all, it is small, usually about 0.5 to 1.5 inches long with the largest of these fish growing to 3 inches. It is brownish gray with small speckles. It doesn't look special with its slender body, and rounded fins. Looking closer doesn't say much, at least in the beginning.

This killfish is found along the coasts of Florida, through the Carri bean, along the Yucatan Peninsula, and along the north eastern coasts of Venezuela to Brazil. It lives in shallow often muddy brackish waters. While there are a small number of fish to live in these habitats, the Mangrove Killfish isn't alone.

Light colored Mangrove Killfish are found in shallow waters that have light sediment bottoms. Dark colored Mangrove Killfish are found in shallow waters that have dark sediment bottoms. A true sign of natural selection through predators. This killfish is often eaten by other fish and the many wood storks of its habitat. In fact, it may also be eaten by the Atlantic Saltwater Snake who often shares burrows with the small fish. But this isn't unusual for a fish of this size.

Like many killfish it eats an unexciting diet that includes ants, flying insects, aquatic worms, mollusks, and mosquito larvae. It may also get cannibalistic in nature during dryer spells. Things begin to get unique for the killfish when you observe it jumping from the waters to catch land insects, including termites, and then returning to the water to eat them. But what is truly amazing is how this animal survives during the dry seasons.

Many of the habitats that the Mangrove Killfish lives in have seasonal dry spells. These can include brackish ponds, marsh lands, and other shallow waters. During these times the Mangrove Killfish will crawl into crab burrows, particularly the Great Land Crab in Florida Here they will live with one another even when at other times they are highly territorial. The crab burrows contain water for longer periods of time then the shallow pools that these fish call home. However, they too dry up in the driest of times. It is then that the killfish does something very unique. Hundreds of killfish will wiggle there way into the hollows found in falling branches, logs, and trees. These hollows are usually created from beetle larvae or termites and become the moist homes of hundreds of killfish.

Once out of water, the Mangrove killfish makes some amazing changes to their bodies. Their thin skin allows them to absorb oxygen directly into their blood veins. At the same time their thin skin allows them to discrete nitrates and other waste products. Their gills fill with cell masses that allow them to retain water and nutrients, while at the same time holding them apart so they won't fuse. During the time on land they won't eat or drink, but will remain active. Other fish who can live on land for short periods of time go into a state of dormant living, but the Mangrove Killfish can spend as many as 66 days on land without doing this.

Once the waters return and their natural habitats become moist and sufficient for life, they will wiggle their way out of the burrows of trees, from under moist leaves, and back to the waters where they belong. Life will continue on as normal with feeding frenzies and territorial battles. But their normal life offers some other unique properties to it as well.

The first to fascinate scientists was the breeding patterns of this fish. Most fish are born hermaphrodites, possessing both male and female reproductive organs. A mere 5% of the population is born male and to this day no females have been reported. Most of the fish reproduce within themselves, producing self-fertilized eggs that are genetic clones of themselves. The eggs, usually 40-75, are then released from the body as tiny embryos waiting to hatch. They don't need water, but just a moist environment to survive.

After 2-4 weeks those that have not been eaten by their parents or other killfish will hatch as tiny versions of their parent before them. After a mere 90 days these fish will be ready to reproduce themselves. Many will continue on with hermaphroditic reproduction, but a few will lay unfertilized eggs for a male to fertilize later. After about 3-4 years many hermaphrodites will become male, loosing their female reproductive abilities.

This makes these occasional land dwellers of utmost fascination. Not only are they the only known fish to live on land throughout times of the year, but they are also the only naturally occurring self fertilizing vertebrate. These two factors alone would be enough to have scientists fascinated in the small creature, but that isn't where their uniqueness ends.

One last factor about this small fish has fascinated scientists. This is a highly adaptable fish. Not only does it spend time with little or no watter, it is known for living through a wide range of changes. It can live through huge changes in temperature, water quality, water levels, and even oxygen levels. But that isn't it. This fish is also known for moving across land to new waters, especially when the old waters become too harsh or a predatory fish species lived there.

While this alone would classify this fish as highly adaptable, no one understand just how much this fish can take. It is one that is extremely capable of living in pollution and dealing with polluted waters on a regular basis. It is this amazing ability to handle the most horrible of conditions that makes this fish great for studying more.

One thing that concerns many scientist studying this amazing little fish is the possibility that it could be wiped out. While it is not listed on the Endangered Species lists it is classified as a Species of Concern. This is mostly due to Mangrove trimming and the cutting back of the Mangrove Killfishes habitat for development. However, their habitats are also being destroyed by impounding of the marshes for mosquito control. Due to its unique lifestyle it is often hard to tell just how big the population of killfish is, it could be rapidly and dangerously decreasing from development and mosquito control efforts.

What this little fish could mean for the future is so hard to say. They are amazing creatures though with their ability to survive on land, their unique reproductive patterns, and their adaptability to harsh conditions. It is for sure though, that the Mangrove Killfish will continue to be studied by scientists for years to come. Who knows what else they might surprise us with.