Tuesday, December 1, 2020

A Giant Named Tiny: Rearing a Giant Pacific Octopus

This blog post adapted from a presentation by Ali Redman, Aquarium Curator.

It all started out with the “Light Trap.” So I must begin this story with how we came to have a light trap and why. 

This past spring we joined the Pacific Northwest Crab Research Group, which is a diverse collaboration of crab researchers and managers who monitor larval recruitment of Dungeness crab using light traps with the goal of producing a sustainable Dungeness crab fishery. 

diagram of Light Trap used 
to count Dungeness crab larvae

The light trap is composed of a float attached to a 5-gallon water bottle with a light inside. Zooplankton enter through funnels, attracted by a light inside the water bottle. 
This past spring and summer, PTMSC staff and interns regularly counted the number of Dungeness crab larvae that were in the trap and reported that to the research group. Not surprisingly, lots of other kinds of zooplankton were also found in the trap. See the chart below for an idea of the diversity of “bycatch.”

Sample of diverse bycatch from the light trap

Even on the very first day, we found pelagic (floating in the water column) paralarval octopuses, both red Pacific octopuses and giant Pacific octopuses (GPOs). Raising octopuses from a paralarval stage in captivity is notoriously hard to do, and has only been done twice successfully. Keeping a pelagic paralarval octopus alive requires a kreisel or “jellyfish tank.” So we were not planning on collecting any octopuses from the light trap.

However, on June 10, we noticed an octopus zooplankton that was different. This female GPO was benthic, which means that she attached to things and crawled. We thought perhaps we could raise her without a specialized tank. We named her Tiny, because, well, she was tiny!

octopus as a pararval zooplankton!


During phase 1 of raising Tiny, we used a “muck tub,” a piece of aquarium equipment used for larval fish rearing. It had fine mesh covering the drain and a lowered water level to keep her from climbing out. And because octopuses are so intelligent, we kept the tub stocked with a variety of decorations to stimulate her natural curiosity. Tiny ate a diet of wild caught plankton (zoea and other tiny crustaceans), and enriched brine shrimp.

Tiny the octopus started out in this muck tub!
When Tiny got big enough, we began weighing her weekly. We were very excited to see steady and vigorous growth. Her average growth rate was 2% of her body weight each day! 

Finally, when she was big enough (but still tiny, of course) she was moved to a tank in the aquarium exhibit. Astroturf around the rim and a weighted lid is now required to deter Tiny from wandering.

Here are a few fun facts about octopuses.

GPO vs red Pacific:

2 rows of dots on tentacles=red Pacific

1 row of dots on tentacles=GPO

Sexing Octopuses

Male octopuses have a hectocotylus, on the tip of the third right tentacle.

Tiny doesn’t have a hectocotylus, therefore Tiny is female.

Check out this video titled "Tiny over Time" which documents Tiny's growth during her stay with us here at the Port Townsend Marine Science Center:

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