Mudfisk
Basic Information
Anatomy
The back pair of limbs of the ancestral durospina have fused together into a large backfin while its other three limbs have become paddle-like fins which is uses as for movement.
Its antennae have become larger, thicker and moved down to the bottom of the face. They have become even more sensitive due to the increased amount of chemorecepors and nerve endings inside, but also importantly electrosensory cells are present in thin lines along the length of the posterior antennae.
An internal gas bladder has evolved, this it uses to keep its heavy body afloat during rest and ease the movement through the water, but also it has to a large degree taken over blood oxygenation, and the mudfisk will surface to gulp air from time to time. It swallows this air which then diffuses through special channels from the digestive tract into the gas balder which is lined in small hair like structures which absorb oxygen. This bladder is also connected back to the digestive tract so that excess gas may be expelled through the anus.
The claws of Derespina however have become vestigial in this line and have decreased in size. Now they are only to be used to guide food particles into the mouth.
Genetics and Reproduction
The mudfisk reproduce by polygynandrous spawning, they will release pheromones into the water indicating to others of the same species that spawning will be about to start who will join in, strengthening the pheromone cloud which makes it travel further down stream into the coastal ocean. This allows some of the newly spawned mudfisk to enter river systems other than the ones their parents inhabited, as well as allowing adults from neighboring river systems to mate.
This mass excretion of pheromones' into the water keeps going until the sun sets and the ocean becomes completely dark, which is the sign for the musfisk to all at once release their gametes into the water.
These gametes will then flow on and about in the water column until it bumps into another gamete of a different individual, with which it will fuse on impact and create an egg.
These eggs are covered in a slimy sticky substance but will be small enough to flow in the water for days on end where they will latch onto creatures, debris and other eggs. At some point these will get heavier then the water they float in and sink to the bottom to develop.
Growth Rate & Stages
The eggs will then start to develop on the ocean floor for around two to three weeks, in which it steadily grows larger and larger until it hatches.
This hatchling is in all ways the same as an adult, just way smaller and unable to reproduce. From which it will grow for about a local year before its considered an adult. At about half a local year they will gain an instinct to swim in the direction of the salty gradient lessening, which will lead them to an estuary or river outlet.
Ecology and Habitats
Mudfisk live for the most part in salty and brackish water. They generally stick to the bottom of estuaries and near coast river outlets <100 m deep due to the abundance of food, but they can be found in deeper parts if circumstances arise.
Due to this large stable niche they can be found around the world except for Niylan and the northern coasts of Arctica.
Dietary Needs and Habits
Mudfisk diet consists of prey smaller then itself that live inside the muddy substrate of brackish estuaries, river outlets, and deltas.
They are able to find these prey due to the disturbances in the water that movement makes. Which they are able to pick up due to their large antenna.
When they have sensed their prey they will start to dig and turn over the substrate whilst sucking in the soup of water, debris and prey.
This whole soup gets consumed and due to the mudfisk not having any specialized adaptations to filter out the soil or water. The consequence is that they produce quite a lot of waste.
Additional Information
Perception and Sensory Capabilities
The eyesight of the mudfisk is quite poor, they are only able to see tones of dark and light which it uses to keep afloat and potentially spot predators from above, However it doesn't need its eyesight to be good due to its large and sensitive antenna on the bottom of the head.
These antenna have evolved to be capable of detecting the smallest movement or disturbances in thick mud just to be able to spot its prey. On the other hand the mudfisk is able to detect electrical potentials in the range of 1µV at distance of up to 20m, meaning that it is aware of essentially all motile organisms within a range of 20m, and can sense larger organisms like spike worms considerably farther away. However it is virtually incapable of sensing anything above the surface of the water.
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