Taresians said thank you by stroking the other's cheek with the back of their hand. They (or at least their captured males) partook in mood enhancers. Elaborate hair bands were very common. Yellow sticks with black writing on them were used both in combat and the joining ceremony.
What humans called marriage Taresians called being "joined", and each incoming male was quickly joined to three females. The short ceremony involved lots of candles, and females dressed in red, including a veil for the brides, which circled the man. Sticks were beaten, and symbols drawn on the man's face. He was blindfolded and his hand tied (claimed to symbolize binding their lives together), before being led of.
Their written language was said to be very complicated.
Ninety percent of the species were female and they supplemented their gene pool by mating with members of other species. They achieved this by releasing a retrovirus on nearby planets that infected the host male and began adjusting his DNA, to eventually make him indistinguishable from a native Taresian. The host then started to become Taresian, and due to what was claimed to be genetic memory awakening also became drawn to Taresia.
The host would develop a knowledge of local space, of Taresian habits and even language, and a hostile posture towards the Taresian enemies the Nasari. The Doctor rated this "quite a feat of genetic engineering.".
Once the host reached Taresia, he was welcomed and told (incorrectly) that he had always been Taresian and that the species reproduced by implanting Taresian embryos in females of other species. Absence of the real parents was explained by saying that the father had left the planet in order to implant the embryo. The unsuspecting males were then separated from their shipmates and their every whim was catered for by the women of Taresia. Each male was then "joined" to three females, who mated with him. The women would remove an amount of DNA to sustain their gene pool, and kill the unsuspecting male, hence the Taresians' elaborate deception.
This deception was uncovered by the crew of the USS Voyager in 2373 when Ensign Harry Kim was infected by the Taresian retrovirus. He discovered the body of one of the previous males and escaped the planet. (VOY: "Favorite Son")