The animal is described as 'niedlich' so it can't be a fish, can it? My wild guess is that 'Meerhäschen' is either an old name for (or a mistake in retelling) 'Meerkatze' or also 'Meerkätzchen', mentioned above by Wilfried. 'Meerkatze' is guenon.

My books are all in boxes right now so I can't look in 'Brehm's Tierleben' which is a likely candidate for corroboration if I should be right.

Wolfgang