Lives of contemplation, discovery, and most of all, sharing what they have learned are what the apkallu treasure.  These settlers of aquatic seamounts since ancient times emerged upon the surface world long ago to teach mathematics and engineering to the iaret. They are fishlike in appearance, but adaptable to land in demeanor and ability, treating new neighbors with fascinated exuberance. In tune with the world, they tend to pursue educated and spiritual paths, or training their bodies through discipline and asceticism.
Apkallu are bipedal and their builds range from stocky to round but are surprisingly agile in the water. On land they travel freely and many even live away from their aquatic homelands all their lives. The isolated nature of their original settlements lead to the development of distinct cyprinid, siluriform, and scombrid variations in appearance. Barbels can be found on both males and females, with greater length demonstrating age and wisdom, but are not universal.  Apkallu have gills as well as lungs, and these can give some the appearance of jowls. Bulbous, unblinking eyes take in all about them, interpreting and understanding.
Apkallu favor lives of contemplation and wonder. The world, both waves and wind, is a marvelous place, full of mysteries and stories to be teased apart and discovered. As a people, they prize cooperation and learning. Neighbors help each other, learn from their elders, and teach their young.  These impulses extend to those outside their race, as is shown by their shared history with the iaret. Philosophical as they may be, they are no strangers to mysticism. Their explorations of the arcane are bolstered by their ability to sense invisible and ethereal beings. To apkallu this unseen 'Other Ocean' grants them insight into the underpinnings of reality.
The traditional apkallu settlement is a submerged village on the slopes of a seamount, near one of their storied monasteries. Modern apkallu might live among other races, or in surface settlements of their own kind, but the monastery remains an important touchstone for them. These are centers of thought and learning, and governance by sage advice.
To the outsider, apkallu can seem sedentary however they are unafraid of new experiences. The questions that arise from their meditations sometimes push them from their quiet lives in search of answers. "The traveler should have no marked map, and be unhurried to arrive," is a much heeded proverb among the apkallu. When the journey does end, as all things must, they enjoy good company, comfort, and comestibles.
Some apkallu names have a touch of iaret sound to them, perhaps from historical association. Other names from even older traditions are more unique among surface languages.

Example Male Names:  Appan, Enusat, Hayate, Isiratuu, Renzo, Suusaandar, Takato, Ubar
Example Female Names:  Aneko, Arahunaa, Gemeti, Hana, Iltani, Mushezibti, Okimi Tanit
Ability score increase.  Your Wisdom score increases by 2 and your Charisma score increases by 1.
Age.  Apkallu reach young adulthood at age 16 and have been known to live as long as 250 years.
Alignment.  Apkallu are for the most part placid and contemplative, believing in cooperation with others.  They tend very slightly towards good.
Size.  Apkallu are between 4 and a half feet and 6 feet in height.  Your size is Medium.
Speed.  Your base walking speed is 30 feet.  Your swim speed is 30 feet.
Amphibious.  You can breathe water and air.
Otherworldly Perception.  Apkallu can sense the presence of any creature within 30 feet that is invisible or ethereal.  It can pinpoint such a creature that is moving.
Educated.  You have proficiency in two skills from the following:  Arcana, History, Nature, Religion.
Imparted Wisdom.  You know the Guidance cantrip.
Languages.  You can speak, read, and write Common, Apkallu and Aquan.
Burial At Sea
The traditional ceremony for apkallu who pass away is burial at sea, where the monks of the village descend the seamount slopes, and offer up the remains of the deceased to sharks and barracuda. In this way, their bodies are returned to the water, and their soul is freed to depart beyond the Other Ocean.

Bettara Fair
Seasoning and preservation of vegetables is both practical and a culinary art among the apkallu. The Bettara Fair is a Mid Stok celebration where pots of pickled kelp and other undersea flora are unsealed and the choicest bits are shared and eaten while still undiluted with seawater. Pickled vegetables apkallu style are immensely spicy to surface palates un-used to eating everything in saltwater.

Apkallu hatch from eggs, but fertilize and carry them internally, giving the appearance of having live birth. Clutches range from one to four fry.

Partners in Civilization
The impact the apkallu had on the iaret goes beyond the intrinsic value of the engineering and mathematics that the iaret learned. This cooperation and learning is part of the iaret myth of empire and the iaret have a cultural predisposition to liking apkallu. A formal greeting from an iaret to an apkallu might replace the usual "master" or "mistress" with "teacher."

Celestial Spheres
Using geometry and mathematics, the apkallu calculated the circumference of Geb in ages past, as well as estimated its surface area and mass. The movement of astrological phenomena has been tracked and measured, but the apkallu are in no hurry to puzzle out the nature of celestial objects. Such things are, after all, quite above and beyond the surface.

Worship and Philosophy
The gods have their adherents among the apkallu, but as a race they are less concerned with deities than, for instance, the iaret. The philosophical schools of apkallu monks are widely varied, but most are occupied with personal conduct and meditative understanding of existence. The gods may or may not blow across the surface of the water, a man must traverse the current regardless.

A Beauty's Physique
The most traditional teachings of apkallu emphasize an aesthetic of clean living, where hard work, self-denial, and meditation upon the suttas leans to purity of body, with shiny scales, clear eyes, and splayed fins. Contact with the surface and distance from traditionalist lamaseries has brought more variety to the pursuit of personal beauty and ornamentation among the apkallu. Colorful water silk clothing, beaded jewelry in coral, gold, and gemstones, and fin or lip piercings are all part of apkallu fashions.