Rock-Eater Fish
Basic Information
Anatomy
The rock-rater fish is a derived Katharaian protosegonid that has adapted its forward facing mouth to filter sediment as opposed to water. The rock fish has therefore undergone significant changes to it’s mouth and throat structure to both draw in and filter the sediment. The throat of the rock-eater has developed the ability to move both towards and away from the end of the mouth. The rock-eater is capable of moving it’s throat back into its mouth to draw water and small sediment in, creating a suction motion. The rock eater has also developed the muscular structures required to seal its mouth as well, enabling it to prevent sediment and water from falling out of its mouth while it is funneled through the throat and into the stomach.
Once inside, the sediment is funneled back into the stomach, along with any water in its mouth. Porous membranes filter the flowing water and sediment. Water is sent through the stomach and expelled from the body by the posterior anus, leaving the sediment and organic matter trapped in the stomach. Heavier, indigestible sediment is trapped in the foremost layers of tissue to be spat out, while digestible matter is trapped further back. The rock-eater fish then spits out the heavier sediment and releases digestive fluid into its stomach to digest food. Digested material is filtered into the bloodstream at the back of the stomach, while the remaining material is vomited out.
Interestingly, in addition to enzymes, the rock-eater fish also employs chemochoids that digest the inorganic material and break it down to its constituent parts. These byproducts can be used by the rock-eater fish to synthesize its own proteins.
The respiratory and circulatory system of the rock-eater fish have undergone significant changes. The gill fronds are no longer located at the base of the organism, but rather are on the sides. This prevents them from being trapped under the rock-eater fish or being damaged by the sediment below them. Blood moving from the gills into the creature connects to a long, central cavity with specialized muscular tissue surrounding it. This muscular tissue pumps the central cavity in a singular direction, however it can do little more. While primitive, this system does ensure that the rock-eater’s tissues are saturated by oxygenated haemolymph. The cavity network has thus grown much more complex, and most of the Rock-Eater Fish’s body is permeated by small, narrow passageways transporting haemolymph to muscles and organs.
The rock-eater fish has a unique fin structure among Katharaians. While most of its relatives have round medium-sized fins, the rock-eater fish has long, bony fins equipped with a claw on each end. This claw is made of keratin surrounding a hard cartilaginous center, and is used mainly for defense. These fins are supported by two bones, which run down the sides of the creature near the base of the head. These bones are used as an anchor point for the fin muscles, reducing the internal stretching required to anchor the fin to the stem. The posterior stabilizing fins of the Rock-Eater fish have dramatically increased in size, and possess a claw; this claw is significantly smaller than the one found on it’s four main fins, and is likely only useful in kicking up loose sediment. The tail fin has also grown, however it has seen a reduction in cartilage across the outermost portions of the fin. The base of the fin is fully supported with cartilage, however the ends of the fin are supported by two bands of cartilage - one on each side.
The foremost gill fronds on the organism have all but disappeared, and all that is left of them are two small, thin hairs that are about 16 cm in length. Interestingly, these organs are packed with nerve endings, and take a shape similar to the whiskers of carnivorans on earth. These “whiskers” are used by the rock-eater fish to help it detect what kind of sediment is directly underneath it’s mouth. While it’s eyes remain it’s primary sensory organ, these whiskers help the organism determine if the sediment beneath it is soft enough to suck up and filter. They can also serve as an early warning system, in case a burrowing predator is beginning to come up beneath it.
Vrachosari trefona - The Rock-Eating Imp
The rock-eating imp is a diminutive relative of the giant rock-eater, and possesses a few unique anatomical features - most notably its size. The rock-eating imp possesses far smaller pores in it’s filtration membranes, and actually possesses an additional gland-like structure at the very base of the throat. This gland like structure cultivates additional chemochoids used to digest the inorganic silts that funnel into the stomach.
Vrachosari megalostoma - The Giant Rock-Eater
The giant rock-eater is quite different anatomically from it’s smaller cousin, despite sharing much of its overall anatomy with them. While it lacks any specialized glands for the purpose, the giant rock-eater actually cultivates a significantly greater variety of chemochoids within it’s stomach and throat, which it cultivates directly in the folds of it’s porous membranes. The giant rock-eater also possesses additional nerve endings within it’s muscles lining the stomach, as well as additional muscle structures along the organ - enabling it to perform physical digestion to some degree. The lining of the stomach is far tougher as a result. While this system of physical digestion is not efficient enough to grind larger stones into digestible powder (those get regurgitated), it is enough to aid in the digestion of slightly larger stones and expose more surface area to the chemochoids that it maintains a symbiotic relationship with.
Genetics and Reproduction
All members of the genus Vrachosari are diploid hermaphrodites, and develop one male and one female gonad. While both members of the genus employ seasonal mating in the far northern and southern regions of their range, they lack this quality in the equatorial regions. Rock-eater fish know when it is time to mate due to a small gland in their brains that is connected to the small vestigial remnants of primitive eyes running along the sides of the organism. These light-sensitive cells cannot aid in vision, however they do allow the rock-eater fish to undergo hormonal responses to the changes in the length of the day. These signals are transmitted to this gland in the brain, called the neurocircadia, which can combine this information with visual input from the eyes. Interestingly, the neurocircadia also has the ability to keep track of the passage of time based on lighting cues, and can keep a basic record of recent lighting and temperature conditions. When conditions are deemed favorable (usually corresponding to the conditions of a particular time of year when closer to the poles) for several days or weeks in succession, the neurocircadia triggers the release of reproductive hormones, triggering activation of the gonads and a mating response in the rock-eater.
Vrachosari trefona - The Rock-Eating Imp
The rock-eating imp mates during the middle of the local spring near the polar regions, however in the equatorial portions of its habitat it is able to mate numerous times throughout the year. When it comes time to mate, the rock-eating imps will begin to secrete pheromones which diffuse into the water and can be detected by other fertile rock-eaters. The rock-eating imps will gather in large schools of 30-40, and gather in an area with very soft sediment. The imps will then dig small, shallow holes into the seafloor and lay their eggs in clutches of 15-35; after which, they will move to another cluster of eggs and fertilize them. Once this process is complete, they will bury the eggs, and the school will disperse.
Vrachosari megalostoma - The Giant Rock-Eater
The giant rock-eater employs a slightly different strategy than its smaller cousin in reproduction. giant rock-eaters mate in the mid-summer near the poles, and in equatorial regions they mate all year. Much like their cousins, the rock-eating imp, the Giant Rock-Eater releases pheromones into the water to attract mates. However, unlike their impish cousins, giant rock-eaters do not gather into large schools to mate - nor do all giant rock-eaters secrete pheromones. In order for a giant rock-eater to secrete pheromones, it must have crossed a specific size threshold (approx. 1.2 meters) and be sufficiently well nourished. The vast majority of giant rock-eaters will not secrete pheromones, and will instead journey towards those giant rock-eaters who do. Rarely will this journey go unimpeded by other rock-eaters and occasionally fights do break out, with competing rock-eaters using their hard lateral fins and claws to attack their rival. eventually, a pair of giant rock-eaters will form and dig two small holes. Each will lay their eggs in a hole, and fertilize the other’s eggs before dispersing to mate again if able.
Growth Rate & Stages
Vrachosari trefona - The Rock-Eating Imp
The rock-eating imp eggs incubate for approximately 5-7 local days. During this time, the buried egg supports the developing juvenile with a small yoke, which provides sustenance and oxygen to the embryo. After the eggs hatch, a naiad emerges as a smaller version of an adult. The naiad digs itself out of the sediment using it’s lateral fins, and once it emerges it swims upwards through the water column.
The young naiad will swim upwards until it is at least 2-4 meters above the benthic layer, where it is safer from the smaller benthic predators that would otherwise feed on them. One of the only notable differences between the naiad and the adults is that the naiad lacks the chemochoids that help the adults digest inorganic substrate. Largely because of this reason, the naidad choose to feed on plankton in the shallow pelagic zones for their first few days of life, until they can attain a slightly larger size - usually around 10 cm - over the course of about 5-10 local days.
Once they accomplish this, they will journey back down to the benthic layer and take their first gulp of sediment. In doing so, they will gather the first of the chemochoids that are essential to their species digestive system. The chemochoids will rapidly colonize the juvenile’s digestive tract, and will form a symbiotic relationship with it for the rest of the rock-eating imp’s life.
The imp will continue to grow until it reaches approximately 25 cm, which normally takes about 2-4 local weeks. Once it reaches this phase of life, the rock-eating imp will be fully developed and able to reproduce. When the conditions are correct, such as reaching the local early spring or being in favorable equatorial waters, the young adult will undergo a mating response and begin the cycle anew.
Vrachosari megalostoma - The Giant Rock-Eater
The giant rock-eater employs a similar strategy to its relative, however due to its larger adult size it undergoes longer developmental periods. However, this is not true for the incubation phase, which lasts 5-7 local days, much like it’s smaller relative. From this egg, a small naiad no longer than 4 centimeters hatches and begins to dig itself up out of the sediment.
When the naiad is able to dig itself out from the nest, it will begin to swim along the seafloor. Unlike it’s smaller relative, the giant rock-eater naiad is born large enough to filter the fine sediment near where it hatched. As a result, the naiad does not need to swim upwards in the water column, and will instead rely on it’s vision and sheltered areas to detect and avoid predators, respectively. As a result of this difference in lifestyle, the giant rock-eater is able to build its colonies of chemochoids far earlier on and will benefit from a more efficient digestive system early in life, however it will also have to contend with increased predation. Overall, at least half of all naidads will die in this phase due to predation alone.
The giant rock-eater continues to grow it’s entire life, however it’s growth rate slows significantly as it approaches a meter in length - a size it is likely to reach after 4-8 local weeks. Around this time, it’s gametes begin to develop, and once this development is completed, the juvenile is considered an adult.
Ecology and Habitats
Vrachosari trefona - The Rock-Eating Imp
The rock-eating imp has a very small range - in fact, the smallest out of any Katharian. The small range is due to the dependence on the rock-eating imp on very shallow waters - something that is a rarity near it’s evolutionary “home” on the Katharaian Ridge. The only reason that a secondary ridge was able to be colonized was due mainly to luck, as some fortunate drifters were able to reach this ridge before starvation onset at the end of their filter-feeding phase. However, due to genetic drift being magnified, this population has diversified into a secondary subspecies, which is smaller and able to supplement it’s diet with normal filter feeding.
Due to its smaller size, the rock-eating imp can only feed on soft sediment with smaller grains. As a result, it is able to successfully engage in niche partitioning with the Giant Rock-Eater, which can feed on heavier sediment with larger particles.
Vrachosari megalostoma - The Giant Rock-Eater
The giant rock eater has a far larger range than it’s relative, as it’s developed a reproductive strategy that allows it to cease its dependence on being able to swim up and down the water column. As a result, they have begun spreading all across Almaishah, wherever it is shallow enough for the planktonic organisms living amongst the sediment to survive. While they are not yet present globally, they have continued to spread slowly across the planet. This advance has been slowed by increased predation and competition along the western coasts of Yama and the Yama-Kub Shay reef system, and the increase in the concentration of sulfur within the water closer to Niylan.
Dietary Needs and Habits
Vrachosari trefona - The Rock-Eating Imp
The rock-eating imp mainly relies on softer sediment with smaller particles closer to the photic zone. This sediment is rich in organic material and easy to digest, allowing the rock-eating imp to easily consume small clumps at a time. This also allows it to niche partition with the giant rock-eater, which prefers heavier sediment that may or may not be as rich in organic material.
Vrachosari megalostoma - The Giant Rock-Eater
The giant rock-eater is a far less picky eater in comparison to the rock-rater imp. Due to its larger size, it is able to consume larger clumps of sediment, including sediment with larger grains. As a result, it has evolved to be a far less picky eater and can eat almost any form of sediment (so long as it has a fine enough grain to consume) that contains photic-layer organisms small enough to digest. In places where it shares its ecosystem with a rock-rating imp, it will generally avoid the finer sediment to avoid competition with the rock-rating imp - preferring the uncontested coarse sediment.
Additional Information
Perception and Sensory Capabilities
The rock-eater fish relies primarily on its camera-type eyes to see the world around it. It’s eyes are organized into two pairs, each on the lateral sides of the head. The pairs are distantly spaced, giving a wide range of view. However, unlike their fellow Katharians - the sea sweepers - the rock-eater fish cannot perform stereopsis. Instead, it’s brain estimates the depth based on color cues, size, and movement. This method is not as accurate as stereopsis, however it allows the rock-eater fish to guess how close a potential predator is to it with enough accuracy to flee (at least so long as it or the predator is actively in motion).
The eyes of the rock-eater fish also possess cone cells susceptible to the blue zone of the light spectrum. This allows the rock-eater to differentiate between the blue ocean around them and the animals and sediment.
In addition to this, the rock-eater fish’s optical center in their brains have split into four sections, each of which corresponds to its nearest eye. These portions of the optical-brain both control the muscles that move the eyes and process the information. These sections are connected by a central mass of nerves, which also connects this portion to the rest of the brain. Thus, the rock-eater fish is able to move all of its eyes independently, allowing it to see a far greater range of vision with greater precision than most other organisms at this time are capable of.
The portion of the brain that detects motion in the rock-eater fish has also swelled considerably in comparison to its ancestors, and as a result the rock-eater fish can quickly detect movement. When doing so, it will usually lock onto the object with one of its eyes until it can determine what caused the disturbance.
Another key adaptation of the rock-eater fish is it’s repurposing of its front two gill fronds into whisker like feelers. With the use of these whiskers, it can detect the sediment directly below it, which also serves to let the rock-eater fish know that it is positioned correctly to suck in loose sediment. In doing so, the rock-eater fish enables itself the ability to continue to use it’s eyes to look out for predators while it feeds.
Symbiotic and Parasitic organisms
The rock-eater fish rely on several species of chemochoids to help them assimilate inorganic materials into their biomass. Another species that it relies on is the mycoid, which helps to digest detritus and convert it into assimilable material.
The specific combination of these different organisms varies from organism to organism, and between species (mycoids and chemocoids are more common in rock-eater imps by percentage of symbiotic microbes), however all of these organisms are present within the digestive tract of all rock-raters. This symbiosis is essential to the rock-eaters' survival, and without them the genus would surely go extinct.
EXTINCT
Genetic Ancestor(s)
Scientific Name
Vrachosari sps.
Origin/Ancestry
Xenosegmenta
Lifespan
V. trefona: 10 local years V. megalostoma: 30 local years
Average Height
V. trefona: 6 cm
V.megalostoma: 20 cm
Average Length
V. trefona: 30 cm
V.megalostoma: 1 m
Geographic Distribution
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