An older pic of Kestrel before I changed a lot about her, which has many anatomical issues that I rather dislike, but I'm going to post it anyway because I have an emotional attachment to it. :D
When the sludge hippocampus evolved from the more generic river hippocampus, in order to take advantage of the sprawling habitat offered by the sewers of large cities, it found a niche rich in food and hiding places, where it could grow to unprecedented size. Unfortunately, the goldfish had gotten there first.