Autonomous Fish Respirometer (FRESP)

Introduction

In the deep oceans large predatory and scavenging fish search across the seafloor for food. One of the big questions about these fishes is how much food they need to survive, and how they are adapted to exist in a cold, dark environment with poor food supplies.

As deep-sea fish don't survive well when they are brought to the surface the Autonomous Fish Respirometer (FRESP) was developed to take measurements of the metabolic rates of fish while they are still on the seafloor. Metabolic rates are a measure of how much oxygen (O²) the fish uses per hour, and as oxygen is required by the fish to use (metabolise) their food their metabolic rate reflects the amount of food that the fish uses per hour.

Methods

FRESP is an autonomous lander and is allowed to free-fall to the seabed. Fish are attracted to the lander by bait (Mackerel) and then trapped in a sealed chamber by the lander.

While the fish are in the chamber their behaviour is recorded by a video camera, and water from the chamber is pumped to an oxygen sensor. A series of pumps and valves switch the flow of water over the sensor so that it alternates between O² measurements inside the chamber and from the ambient (outside) water. This means that if the sensor readings drift the data can be corrected so that we get the correct readings from the chamber.

Results and discussion

FRESP has taken measurements of metabolic rates in two species of fish in the North Atlantic Ocean (the grenadier or rattail Coryphaenoides armatus and a deep-water eel Synaphopbranchus kaupii), and a species of shrimp from the Mediterranean (Acanthephyra eximia). The first results showed that Coryphaenoides armatus used oxygen at a rate of 3.6 ml O² per kg per hour. For comparison Atlantic cod (Gadus morhua), which is related to grenadier fish but lives much shallower, uses oxygen almost 10 times as fast. This means that the grenadier fish Coryphaenoides armatus needs to eat much less food in order to survive.

Contact

Dr David Bailey, Research Fellow
Telephone: +1 858-534-4858 ext 17

Email: oceanlab@abdn.ac.uk