Scientists need to understand how gill development limits fish growth

January 06, 2021

The distribution and concentration of dissolved oxygen and water temperature in the oceans and freshwaters are usually far more influential in shaping the growth and reproduction of fish than the distribution of their prey.

In a new paper in Science Advances, Daniel Pauly, principal investigator of the Sea Around Us initiative at UBC's Institute for the Oceans and Fisheries, argues that scientists need to avoid attaching human attributes to fish and start looking at their unique biology and constraints through a different lens.

This lens is Pauly's own Gill Oxygen Limitation Theory (GOLT), which explains many features of fish biology and whose core principle is that as fish grow, the surface area of their gills - their respiratory organs - can't keep up with the oxygen requirement of their bodies.

The GOLT emphasizes that gills are surfaces through which water must flow - a bit like the wind through blinds. Gill surface area grows in two dimensions, that is, in length and width, but they cannot keep up with bodies that grow in three dimensions, length, width and depth. Thus, as fish get bigger, they have less gill surface area and their gills provide less oxygen per unit volume or weight.

"The problem is that many colleagues fail to understand the basic geometry of gills, and argue that, as fish grow bigger and, thus, require more oxygen, they can just grow larger gills," Pauly said. "But they can't pack their heads full of gills because, if that were to happen, water wouldn't be able to flow through."

Pauly's research indicates that the gill issue is a constraint, not something fish can evolve out of. This means that once their gills reach a point where the oxygen they supply cannot support a bigger body, they stop growing.

"This is particularly important in the context of climate change because warm waters contain less oxygen. This means that gills have less oxygen to supply to bodies that require more oxygen at higher temperatures", Pauly said, "This double whammy occurs because fish cannot maintain their body temperature constant, and higher water temperatures accelerate their metabolisms."

Higher temperatures force fish to stop growing at a smaller size, given the little oxygen available to them. This has important implications for fisheries and aquaculture.

Despite having many applications, the GOLT has been the subject of criticisms. In this new paper, Pauly responds to these challenges point by point.

"In contrast to regular scientific papers, the 'data' here are published arguments against the GOLT and their counterarguments, presented in table form. These arguments are not serious; they are more like barnacles on the hulls of a boat, which slow it down but do not sink it", Pauly said. "They are based on a lack of understanding of key geometrical and biological concepts. Thus, it was important to clear them out so that the GOLT can start to be seriously studied, and its real problems addressed."

The fact that the Gill Oxygen Limitation Theory is mainly qualitative and makes few quantitative predictions, is one of the real problems that Pauly himself has noticed and would like his colleagues to address, as well as the fact that it doesn't deal with bioenergetics and the role food plays in the life of fish.

"Food is necessary for life and the GOLT is structured around the notion that there is enough food but what if there isn't enough food? The relationships between food and oxygen will have to be studied, too," he said.

University of British Columbia

Related Fish Articles from Brightsurf:

Fish banks
Society will require more food in the coming years to feed a growing population, and seafood will likely make up a significant portion of it.

More than 'just a fish' story
For recreational fishing enthusiasts, the thrill of snagging their next catch comes with discovering what's hooked on the end of the line.

Fish evolution in action: Land fish forced to adapt after leap out of water
Many blennies - a remarkable family of fishes - evolved from an aquatic 'jack of all trades' to a 'master of one' upon the invasion of land, a new study led by UNSW scientists has shown.

How fish got onto land, and stayed there
Research on blennies, a family of fish that have repeatedly left the sea for land, suggests that being a 'jack of all trades' allows species to make the dramatic transition onto land but adapting into a 'master of one' allows them to stay there.

Fish feed foresight
As the world increasingly turns to aqua farming to feed its growing population, there's no better time than now to design an aquaculture system that is sustainable and efficient.

Robo-turtles in fish farms reduce fish stress
Robotic turtles used for salmon farm surveillance could help prevent fish escapes.

Heatwaves risky for fish
A world-first study using sophisticated genetic analysis techniques have found that some fish are better than others at coping with heatwaves.

A new use for museum fish specimens
This paper suggests using museum specimens to estimate the length-weight relationships of fish that are hard to find alive in their natural environment.

Reef fish caring for their young are taken advantage of by other fish
Among birds, the practice of laying eggs in other birds' nests is surprisingly common.

Anemones are friends to fish
Any port in a storm, any anemone for a small fish trying to avoid being a predator's dinner.

Read More: Fish News and Fish Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to