Juan Manuel Borrero / Pearl cichlid (Geophagus brasiliensis) captive, occurs in Brazil and Uruguay.

Juan Manuel Borrero / Oscar (Astronotus ocellatus) captive, occurs in South America.

Jane Burton / Siamese fighting fish (Betta splendens) 'phantom' coloured male displaying to a female, captive from Malaysia and Thailand.

Alex Mustard,Alex Mustard / A nudibranch (Dendronotus frondosus) photographed in the field aquarium, Gulen, Norway. North East Atlantic.

Alex Mustard,Alex Mustard / Nudibranch (Flabellina nobilis) photographed in the field aquarium in Gulen, Norway. North East Atlantic Ocean.

Cheryl-Samantha Owen / West coast rock lobster (Jasus lalandii) captive at Two Oceans Aquarium, Cape Town, South Africa.

Stephane Granzotto / Malaysian jellyfish (Sanderia malayensis) in aquarium with purple lighting.

Stephane Granzotto / Moon jellyfish (Aurelia aurita) in aquarium with purple lighting.

Stephane Granzotto / Moon jellyfish (Aurelia aurita) in aquarium with purple lighting.

Stephane Granzotto / White spotted jellyfish (Phyllorhiza punctata) in aquarium.

Stephane Granzotto / White spotted jellyfish (Phyllorhiza punctata) in aquarium.

Felis Images / Striped panchax (Aplocheilus lineatus) in aquarium. Occurs in India and Sri Lanka.