Leviathan

Leviathans, also called Sea Dragons, are an amphibian genus of slenderfish who live in warm waters of Midoria, mostly in the Dragon Sea (named after them). They are known for their huge size and ferocity. The two most known stages of the leviathans' life cycle are the second larval, or "fish" stage, and the juvenile, or "dragon" stage. In reality, the leviathan's life cycle consists of six stages: First larval, Second larval, juvenile, pupa, adult, and senile.

Diet and Feeding Habits
Fish stage leviathans feed on smaller fish and other aquatic creatures. Juvenile leviathans eat larger fish and canibalize weaker juveniles, often after a battle for dominance. An adult or juvenile leviathan will never eat a female, either in juvenile or fish stage. This has given fishers the opportunity to carry young fish females in cages around their ships to protect themselves from adult leviathans. Note that juvenile leviathans may still try to attack the ship if they mistake it for a predator.

Juvenile and adult leviathans eat mostly at night, especially if it's full moon.

Senile leviathans without a guest eat mostly plankton.

Mating habits
The mating habits of leviathans depend on their current stage of development. For juveniles, mating comes after a battle for dominance and is done by copulation. For adults, mating is done by spraying sperm on the females.

Juveniles
When male leviathans enter the juvenile stage, they will compete for the females' favors. When two male leviathans compete for the dominance of a female school, other juveniles will gather around the competitors and start circling them. The battle ends when a competitor castrates or kills the other. Castrated competitors are pursued by the pack, and more often than not, they end up being eaten by them.

If a juvenile castrates the competitor, it eats its gonads to increase its alpha hormone production (see Lifecycle, Adult Stage). The more competitors a leviathan manages to castrate, the sooner it will enter the adult stage.

When a juvenile manages to kill a competitor, it eats the liver away. Leviathan liver contains a greater amount of alpha hormone, and allows a juvenile to enter adult stage earlier.

After winning a battle, the pack is focused on either eating the carcass of the loser or driving it away, allowing the winner to impregnate the females by copulating with them.

Adults
Leviathans in the adult stage dominate a school completely and drive the male pack away. After the males are pushed away from the females, the adult circles the females and surrounds them with its body until the females are all packed together in a tight group. Then, the leviathan sprays its seminal fluid on the females, and uses its body to create a vortex where the females are located. The vortex attracts the seminal fluid, maximizing the probability of impregnation. The Impregnation success is high enough to ensure the adult to have many descendants, but low enough to conserve the genetic diversity on the school.

Seniles
Senile leviathans suffer a partial atrophy of their digestive and reproductive organs, and must seek a dominant juvenile to inhabit their stomach for symbiosis. A senile's stomach develops a prostatic orifice whose anatomy is similar to a female vulva. This orifice is connected to the senile's prostate via a secondary seminal duct. When the senile encounters a female school, it encircles them while the juvenile penetrates its prostatic orifice. After the juvenile ejaculates inside the host's prostate, the host is ready to spray the females with the juvenile's sperm. Stomach symbiosis and prostatic orifices are common to most slenderfish in Midoria, but leviathans are the most representative example.

First Larval Stage
Leviathan Larvae hatch from inside their mother. In this stage, leviathans resemble maggots, and they contain underdeveloped lungs and gills that allow them to breathe both water and air. After they're born, the larvae start eating their mother's tissue, starting by the womb. After they finishing eating their mother's internal organs, the larvae enter a brief metamorphosis period where their outer skin becomes a small but hard cocoon.

Second Larval or "Fish" Stage
After shedding their larval cocoon, leviathans have acquired bones, muscles, fish scales, gills, fins and natatory bladder. They exit their mother's cocoon by secreting a digestive enzime which dissolves the cocoon and allows them to eat the cocoon away. After hatching, leviathans collapse and seal their primitive lungs. They are unable to breathe air at this point.

After they have hatched, the fish leviathans organize into schools for survival, and eat other fish and aquatic lifeforms. The maximum size of a second larva leviathan is nine meters. This is the form normally fished and eaten by humans.

It should be noted that while leviathan fish are tame and don't contain scales or strong jaws like juveniles, they're dangerous enough to defend themselves against attackers; there have been cases of leviathan fish attacking and even eating humans, although these cases are rare and usually involve inexperienced and aggressive fishers. It's normally recommended for fishers to sedate leviathans and carry them in underwater cages for their transport to safer waters; but it's safer to rely on leviathan farms where their lifecycle is controlled for human consumption.

Pupa
When a male leviathan enters puberty, it forms a cocoon by spitting a silk which solidifies with air. With time, the cocoon strands begin to straighten, forming sharp and thin spines which protect the pupa from predators. When the metamorphosis is finished, the males secrete the digestive enzyme through their skin, dissolving the cocoon and breaking out as juveniles.

Females enter pupa stage after becoming pregnant; but unlike males, their metamorphosis is reverse: They revert to first larval stage to allow the offspring to consume the mother's body from inside. This reverse metamorphosis is triggered by a particular hormone called Lev-F-Beta1, and has been proven experimentally to affect both males and female leviathan fish when exposed to it. In other experiments, fertilized eggs have been cultured in captivity without being exposed to Lev-F-Beta1; the hatching leviathans come out already in fish stage.

It is theorized that the female pupa (and the consequent first larval stage in the offspring) was a recent evolutionary adaptation that provides the hatchlings with nutrients and a predator-free space to grow and develop. When exactly did this evolutionary adaptation occur remains a mystery; some oceanologists say that the most probable cause was a random mutation that activated a latent gene remnant from earlier evolutionary stages. Other species of slenderfish also exhibit cocoons and first larval stages.

Juvenile or "Dragon" stage
Males and females enter juvenile form in separate ways. Females develop their reproductive organs and change color, while males form a cocoon and become pupae.

After coming out of the cocoon, the leviathan has become a juvenile or dragon. Juvenile leviathans resemble snakes: Its bones are thicker and more resistant, its muscles are stronger, and its lungs are developed to full capacity. The rib cage is also expanded and the jaws are widened and strengthened to catch larger prey. The scales are hardened and contain denticles, giving them more resistance and greater swimming speed. Juveniles have also developed external reproductive organs which they use for couplation.

Of all stages, the Juvenile stage is the most dangerous stage of a leviathan: They are strongly territorial, and will defend their school against any perceived threat, be it other juveniles, predators, or human hunters. Juvenile leviathan attacks are the most frequent cause of death at sea, surpassing attacks by sharks, crocrays, medusae and even krakens.

On the absence of female competitors, a juvenile begins to search for a senile leviathan to inhabit. If it doesn't find one after a few weeks of searching, it enters adult stage.

Adult, "Alpha" or "Giant" stage
The adult stage is also known as the Alpha stage. Alpha leviathans emit large quantities of a hormone that indicate their dominant status to both competitors and females. This hormone is produced in the males' livers, and they're often hunted for its aphrodisiac properties. The alpha hormone, also called Lev-M-Alpha1, is an active component of the "Ignite" aphrodisiac. Fortunately for leviathans, Lev-M-Alpha1 has been successfully synthesized in labs.

The Lev-M-Alpha1 hormone triggers the following changes in the Alpha: It should be noticed that alpha leviathans rarely come out of the water except to feed on larger prey. Giant leviathans swimming in the surface are usually senile.
 * Its skin darkens
 * Its phalus is shed
 * Its gonads are retracted inside its body
 * It starts to grow a bright dorsal fin, whose color depends on the species
 * It starts growing spines along its dorsal fin
 * It starts growing venomous glands and retractile canines (these produce a paralyzing agent used to hunt larger prey)
 * Its gills enlarge
 * Its pectoral fins are enlarged and grow spines
 * Its metabolism is accelerated, allowing it to grow up to two hundred meters long

Senile stage
After four or five years, an alpha enters senile stage and starts producing a hormone called the Senile Hormone (Lev-MF-Beta2). Lev-MF-Beta2 has a molecular structure similar to the female sexual hormone. It also produces the following changes in the senile:
 * its metabolism decreases
 * it stops emitting the alpha pheromone
 * its gonads are dissolved
 * stomach acid production is reduced to a minimum
 * the esophagus expands
 * the prostatic orifice is developed

Prostatic orifice and duct
The prostatic orifice has its origins on slenderfish's prostatic stomach. The prostatic stomach is a tiny organ which absorbs and filters nutrients digested from the stomach and delivers a pre-seminal fluid to the prostate. As time passes, the secondary stomach degenerates into a simple tube which goes from the prostatic orifice to the prostate. The prostatic orifice itself is created by the same pluripotent cells than the female vulva, which explains its transformation into a vulva-like organ when Lev-MF-Beta2 is secreted.

Symbiosis
When an alpha completes its senile transformation, it starts searching for juvenile packs, and circles them, secreting large quantities of Lev-MF-Beta2. This triggers a battle for dominance in the two most promiment members of the pack, which ends in the loser being castrated and the winner entering the senile's mouth. The guest's Lev-M-Alpha1 hormone and the host's Lev-MF-Beta2 are mutually neutralized, preventing the guest from reaching Alpha stage. After the guest is finished establishing itself inside the host's stomach, symbiosis begins.

In this stage, the host tends to swim to the surface and ingest large quantities of water, rich in plankton and oxygenated, that the guest can breathe through its gills.

Reproduction
In the presence of fertile females, the host reduces the quantities of Lev-MF-Beta2, allowing the guest to secrete more quantities of Lev-M-Alpha1. This turns the host into a sexually active male, which allows the guest to use the host for reproduction.

Late Symbiosis
As the guest grows larger, there comes a point where it can no longer rest inside the stomach. The guest reaches through the host's throat, and its head resides inside the host's mouth, acting as a second jaw.

In this stage, the host resumes its juvenile feeding habits, while the guest consumes the food ingested by the host, excreting partially digested food to allow the host to survive.

End of Symbiosis
When the guest can no longer inhabit the host, it exits by two ways, depending on the guest's status: By explosion, or by assimilation.

Explosion
If the guest's body becomes too wide to fit in the host's esophagus, the guest expands its muscles, exploding the host's esophagus and killing the host by internal bleeding and subsequent heart failure. After the host dies, the guest exits through the host's mouth.

Assimilation
If the host becomes too old to hunt for food, the guest enters the host's trachea and invades its lungs, absorbing the host's oxygen and eating the lung tissue. This drowns the host in its own blood. After the guest has finished opening itself through the lungs, it proceeds to eat the liver, triggering its alpha transformation. The guest then exits the host by eating away its gills. After exiting, the parasite secretes large quantities of the Lev-M-Alpha1 hormone, driving away potential predators and competing leviathans. Finally, the guest eats as much as it can before leaving the scene and scanning its new territory.

Industrial components
The leviathan is a very sought material source for industrial components:
 * The leviathan's cocoon silk is used in bulletproof vests
 * The Alpha pheromone is used for the production of aphrodisiacs
 * The adult scales are used as a base material for high impact armor
 * The spines are also used to synthesize weapon ammunition
 * Adult leviathans' venomous glands are used to produce paralyzing chemicals used for law enforcement and beast hunting.

Ecological concerns
When Leviathans entered the endangered species status in year 97, a global law was issued by the Space Authority to protect Leviathans from excessive fishing and hunting. Leviathan farming plants were created in Hong Kong, Nippon and China. In these, alpha adults were grown and kept sedated in isolated tanks before their execution and industrial processing.