Despite being equines, freshwater kelpies resemble felines in behavior. They can purr, they groom themselves a lot, and they enjoy playing...
They tend to be very aggressive to other big predators (other kelpies, for example) and will chase them off their territory ; they don't necessarily take the risk of killing opponents unless they feel very threatened. Other than potential competitors, they are not particularly aggressive creatures in general, but the sight of a prey can trigger their hunting instincts, especially when they are underwater, as it is their natural response to any movement at the surface. It is not rare to be accidentally bitten by a kelpie if you are not cautious. Best thing is to make some noise at a reasonable distance of the water to make kelpies aware you are not prey.

Most of the time, freshwater kelpies will be seen chilling in their lakes, rivers or forests. They usually prefer to stay in the kelp forests, where their stripes camouflage is the most effective. Kelpies feel safer this way, and more relaxed. When they let themselves be seen, they are less likely to attack as they are not hunting, and don't feel threatened. They are diurnal creatures, and will be active from dawn to dusk, while they will sleep underwater at night. It doesn't mean they can't be active at night, but it is rare.

Most of their activities outside hunting are related to the water, as their presence trigger the growth of red kelp forests they like to take care of. They groom themselves a lot, and will also let birds and fish clean their teeth. Kelpies are usually maniac with their hygiene and the quality of the water, so it's not uncommon to see them get rid of some unwanted elements that could end up in their habitat.

When kelpies reaches maturity (around fifteen years, the equivalent of twenties for humans), they will either start to wander off their parents' territory naturally, or they will be chased away by their parents. Females will quickly find a territory to settle down, usually not far from their parents' one, searching for lands with quality water and prey.
Kelpies stallions will become wanderers, and will start to roam, often entering the territories of other kelpies in the hope to be accepted by a female. If the mare already has a partner, the stallion will most likely be chased away by the couple to avoid the competition for prey.

Kelpies are known to mate for life, so if the mare or the stallion dies, the other one will generally stay alone for the rest of their life. It's rare to see them accept a new partner after the dissapearance of their first mate.
The species suffers from a very slow breeding rate, and it can take years for a couple to have offsprings. They will only breed if they have access to quality resources (mostly food and water). When the female is expecting, the couple will start building a nest underwater, made of kelp and other plants.

Kelpie foals are born with eyes and ears closed, are not able to stand up like most equines, so they are very vulnerable. They entirely count on their parents to survive the first years of their life, and the mare will mostly stay in the nest as she is the one to feed the foal, but the male will also stay with the newborn to keep it warm when the female is gone. Kelpies become more aggressive when they have a foal.

After a few weeks, the foal can swim and discover the lake, but can't breathe the surface's air yet. It takes some months for a foal to be ready to go outside the water, and it is the most dangerous moment of their lives as they are usually very curious and develop their hunting instincts. This is why the parents need to be very attentive as a foal can quickly wander too far and can suffer predation from other creatures. Foals will grow baby teeth around three month old, and will gain their definitive stronger teeth around five years.

Most kelpies will ignore smaller creatures on their territory and will not bother to hunt, as long as they are no threat. Even if they can eat any other creatures, kelpies will prefer bigger prey to not waste their energy. They are mostly looking for deer-sized prey, and even if they live in the water, they do not eat fish. Most of them avoid attacking other talking creatures, as they respect their conciousness, or because they are scared of eventual retaliation, but some kelpies just doesn't care about this and would eat anything.

Kelpies will always hunt during daytime, to avoid conflict with noctules. Their red stripes offer them the ability to blend perfectly in the red kelp forests ; this way, they can ambush prey who would come drinking/swimming in the lake without being noticed too early.
If no prey is coming, kelpies will not let themselves starve and will go off the water, usually to find another pond or river so they can reiterate their ambush method. They can hide in the forest's vegetation as well, but it is rarer as they prefer to attack directly from the water.

They use their powerful jaws to break their prey's neck, but will also use their kelp vines to prevent the animal from hurting or escaping them. Kelpies like to do the work as quickly as possible to return hiding in their lake without being noticed by their freshly killed prey. If they can't drag the prey to the water, they will eat it on land and leave the rest to the scavengers. Kelpies will only eat what they killed themselves, or what a parent/partner killed. They will only eat from carrions if they are starving, which is common for wandering stallions who have no other choice.

Abyssal forms, also called "true colors" or "the other form" by kelpies, are the alternative appearances taken by freshwater kelpies and saltwater kelpies. Other species know less about these due to not witnessing them often but are as essential and useful to the kelpies nonetheless.
Abyssal forms completely change the colors of a kelpie - these colors are random, and have nothing to do with their species or gender. They get longer fish-like tails and various new fins of diverse shapes. Their bodies are covered in a mix of fish-like scales and fur. The eyes' sclera gets very dark, and the gills they earn are located on their neck, flanks, and sometimes tail.

Vasco (freshwater kelpie) showing his abyssal form.

The gills are bioluminescent and the light intensity goes along with their respiration.
The main difference between freshwaters and saltwaters, apart from the size, is that saltwater have multiple see-through parts on their tail and fins, showing their bones inside. They also have a little lantern-like appendage on their forehead, similar to anglerfish, as well as little fins on their ears (a trait that can be observed on freshwaters too, but all saltwaters do have it). Saltwaters also have a lot more bioluminescence on their bodies.

Kelpies can mostly be seen in their terrestrial forms, in which they are still able to swim very well. However, they can shift to their abyssal forms, which are much more fish-like and designed for the water. It is mostly a question of comfort, as freshwater kelpies prefers to hunt in their terrestrial form, enjoying their ability to quickly alternate between land and water to hunt, while saltwaters strictly hunt in the ocean.

Lewis and Kiersten dancing, both freshwater kelpies.

Fins and fish-tails improve the kelpie's mobility underwater and allow them to be faster. The bioluminescence of their gills and some markings are known to be a way for kelpies to communicate with each other as some kind of body language.

Their underwater vision and smell are improved, and of course, their respiratory system is entirely dedicated to breathing underwater, therefore a kelpie in their abyssal form can't breathe the surface's air. They also become more adapted to the various levels of pressure of the water environments.
The shapeshifting can be used at will by kelpies. It takes some months for the foal to master it completely. Foals will discover the surface before the deep waters. Saltwater kelpies are known to be able to dive deeper than freshwater kelpies, due to the fact they live in the ocean. They are also more prone to use their abyssal form than freshwater kelpies.

Freshwater kelpies are not appreciated by most species of the Crater. Their "vicious" ambush-hunting tactics and the fact they can practically kill any creature (even bigger than them) made them have a very bad reputation among the other creatures (pegasi, unicorns, woolies, blue wyverns...). At their time, unicorns were the natural ennemy of freshwater kelpies, and the only creatures who could compete with them in a fight apart from big noctules.

The appellation "water demons" is a good illustration of how kelpies are perceived by these species. Waters are scary for most creatures because it is their natural habitat. Kelpie foals are often the target of other species, as they see an occasion to get rid of a future predator. Many rumors, legends, and songs have been created about kelpies, inspired by the fear of them. One of the most common myths is that their red stripes are made with their victims' blood, which is obviously false.

But kelpies are not hated by everyone. Jaguoons, for example, share a particular relation with the freshwater kelpies, as the red kelp forests they create gives the little felines a very good environment to hide and raise their youngs. The carrions left away by kelpies is also a very nice food resource for jaguoons.
Freshwater kelpies rarely encounter their cousin species as they usually don't go in the same environments for comfort purpose, but some rare freshwater kelpies are accepted in saltwaters' herds and can adapt pretty well. It's common to see a saltwater kelpie with freshwater ancestry in a herd, with more or less traits showing.