Many of the names for Sirotan's friends and family include Japanese name suffixes that are hard to directly translate into English. So, I just left them in the English name, but here you can get a better understanding of what they mean.

-tan : A small child's slurred mispronunciation of -chan. If it is used by an adult at all, the person is most likely either being sarcastic or ironic, unless speaking to an infant or toddler. A non-anime example of this is a certain fast food fried chicken chain's mascot in Japanese advertising, an adorable little girl, "Biscotto-tan," who carries an enormous biscuit on top of her head; her name can probably best be translated as "Widdle Biscuit."

The most important suffix for Sirotan (^_^) as it is in his name. Sirotan's name is childish in the way that the "h" is missing from the "shiro" part which further emphasizes the childish nature of the slurred name, "Widdle Wite." Sirotan uses the suffix for his close friends, Turtle-tan and Penta.

-san = Mr/Mrs/Ms/Miss : It's a mark of respect. You call someone "-san" when you don't know her very much but you don't want to be rude to her or when she has a higher (social) rank than you. However, contrarily to what many foreigners and Japanese alike usually think, "san" is not the equivalent of "mister" or "mrs". For example, "san" can also be used for animals, and not just for cats and dogs, but for any animal. Even a spider can be called "kumo-san" (especially by children). It also works with pictures, so that you could call a tiger or monkey on a painting "tora-san" or "saru-san". Cockroaches (gokiburi), which most Japanese strongly dislike, seem to be the exception that confirms the rule, as almost nobody will give them a suffix at all.

Sirotan uses -san when addressing larger animals than him, or scary ones. For example, he includes it in "Shark-san."

-kun : Generally for male children. Also could be used when addressing a male of lesser status.

Sirotan refers to some of the other boy animals, who aren't as close as his close friends, with "kun." He uses it for "Dolphin-kun."

-chan = little : You say that to someone you have affection for. You generally kindly call a little child "-chan". You can also call a person you've known since childhood that way. That's can also be the "-kun" for the girls. If you have real affection for your elder sister, you can call her (o-)nee-chan. But it can also be used the reverse way, that is calling "-chan" someone you disrespect so much that you consider him as a child.

Sirotan uses this suffix for his grandmother and for his goldfish friends.

Information from Japan Reference.