In the 19th century, upper class homes had serving utensils for each part of the meal.  Fish servers were used to portion and serve fish.  They were often made of silver or silver plate, and these have lovely mother-of-pearl handles.  The knife has lovely openwork, which in addition to being visually attractive, allowed excess liquid to drain before serving.

 

Mother-of-pearl (sometimes called nacre) is the smooth, shiny, and iridescent layer found on the inside of certain mollusk shells, like those of oysters and abalones.   The unique iridescence comes from the way light reflects off its layered structure