Cabrillo Marine Aquarium

Featured Research

Student Researcher Jacob Partida Tracks Fishy Movements

Have you ever wondered what CMA’s fish are doing at night when no one is around? Student researcher Jacob Partida designed a research project to discover the answer to this question. In particular, he wanted to find out what the rockfish in the kelp tank are doing late at night.

“In the wild, many species of rockfish are nocturnal and mostly active at night,” explained Partida. “My thought was that if CMA’s fish are fed every Monday, Wednesday and Friday during the day, then the rockfish in the kelp tank would be more active during the day when they’re fed than at night even though they are known to be nocturnal.”

To test his hypothesis, Partida sat in front of the kelp tank for an hour during the afternoon on Sunday, Monday and Thursday observing and tracking the movements of two kelp rockfish, two treefish, a scorpionfish and two black and yellow rockfish. Then at night he set up a camera and recorded the kelp tank from 5 pm until 5 am to capture the movements of these same fish during the dark, but sometimes it was a little too dark.

“Unfortunately, it got too dark around 7 pm, so I could only get their behavior when it was sun down and sunrise, but sunrise was actually when the janitor turns on the lights in the morning,” said Partida. “So I took a half hour of footage from 6:30 pm and a half hour of footage from 3:45 am and I observed and recorded fish movements during those time periods.”

Based on his observations, Partida discovered that the fish were actually more active during the night despite being fed during the day, which turned out to be the opposite of his hypothesis. But why would nocturnal fish be active during the night if they aren’t able to rest as much during the day?

“Because nocturnal fish are adapted for being active at night and that’s when they are most comfortable. They have bigger eyes so they can see better in the dark and their lateral lines (sense organs that detect movement) are more developed so they don’t have to rely so much on vision,” said Partida. “Their coloration will either be black or brownish yellowish or red so they can blend in easily in dim light and first hand I can tell you they blend in really well.”

Partida also discovered that each fish had established a territory within the kelp tank that they stick to most of the time, especially at night. Since the kelp tank is much taller than it is wide and much longer than it is tall, most of the territories are vertical. For example, one of the treefish almost always stays by a stem of fake kelp anchored at the bottom of the tank that floats up while the scorpion fish always stayed near a tall pile of rocks.

The conclusion based on his observations: When rockfish are moving at night it tends to be up and down. Now we know what CMA’s rockfish are doing when no one is watching.


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