Predatory fish have large guts to help them through famine

Jul 08, 2011 by Lin Edwards report
Yellow perch (Perca flavescens). Image: United States Department of Agriculture

( -- A new study by scientists in the US has solved the mystery of why predatory fish have a far greater digestive capacity than they actually need. The study suggests the reason is that the extra-large guts allow them to gorge on food when it is available so they can store the calories for use in the lean times.

It has long been known that in captivity predatory fish can grow much larger than they do in the wild. Their stomachs are usually sac-shaped and capable of processing enormous quantities of food at a time, and in captivity it is easy to over-feed the fish. In the wild the fish must expend a great deal of energy in foraging, stalking, capturing and then digesting their prey.

The unpredictable nature of has led some researchers to suggest they can store the energy they derive from gorging on food when it is available to enable them to survive periods when prey is not available, but until now little study had been done on the digestive capabilities of . This is the first comprehensive study of the digestive capabilities of wild predatory fish.

In the new study, researchers Jonathan B. Armstrong and Daniel E. Schindler of the School of Aquatic and Fishery Sciences at the University of Washington in Seattle analyzed some 639 recordings of 38 species of predatory fish and assessed the load capacity ratios for their digestive systems.

The researchers found the digestive systems of the were around two or three times larger than they need to be in average conditions. The large gut allows them to capitalize on “pulses of food abundance,” which requires a high digestive capacity, but maintaining that capacity is costly in energy terms when food is scarce and a large gut is not needed.

Armstrong and Schindler developed numerical simulations of the trade-off that exists between having excess digestive capacity and the metabolic cost of the extra guts. The simulations suggest the trade-off benefits the fish only if they experience irregular periods of feast and famine, and that predator/ encounters are less common than previously believed.

The paper is published in the journal Nature.

Explore further: Study shows exception to rule of lifespan for fliers, burrowers and tree dwellers

More information: Excess digestive capacity in predators reflects a life of feast and famine, Jonathan B. Armstrong & Daniel E. Schindler, Nature (2011) doi:10.1038/nature10240

A central challenge for predators is achieving positive energy balance when prey are spatially and temporally heterogeneous. Ecological heterogeneity produces evolutionary trade-offs in the physiological design of predators; this is because the ability to capitalize on pulses of food abundance requires high capacity for food-processing, yet maintaining such capacity imposes energetic costs that are taxing during periods of food scarcity. Recent advances in physiology show that when variation in foraging opportunities is predictable, animals may adjust energetic trade-offs by rapidly modulating their digestive system to track variation in foraging opportunities. However, it is increasingly recognized that foraging opportunities for animals are unpredictable3, which should favour animals that maintain a capacity for food-processing that exceeds average levels of consumption (loads). Despite this basic principle of quantitative evolutionary design, estimates of digestive load:capacity ratios in wild animals are virtually non-existent. Here we provide an extensive assessment of load:capacity ratios for the digestive systems of predators in the wild, compiling 639 estimates across 38 species of fish. We found that piscine predators typically maintain the physiological capacity to feed at daily rates 2–3 times higher than what they experience on average. A numerical simulation of the trade-off between food-processing capacity and metabolic cost suggests that the observed level of physiological opportunism is profitable only if predator–prey encounters, and thus predator energy budgets, are far more variable in nature than currently assumed.

Related Stories

To trust or not to trust your friends

Jan 30, 2007

Sometimes it is better to follow the advice of others rather than your own mind even though you seem to have things under control. Not only humans but also fish follow this doctrine as shown by ecologists Jörgen Johnsson ...

Fish can be picky eaters

Jul 19, 2010

( -- We all know how fussy kids can be about their food, but now new research suggests they're not the only ones.

How to Grow a Bigger Brain

Mar 06, 2006

Hatchery-reared steelhead trout show increased growth of some parts of the brain when small stones are scattered on the bottom of their tank, according to a new study by researchers at UC Davis. The brains ...

Recommended for you

Offspring benefit from mum sending the right message

5 hours ago

( —Researchers have uncovered a previously unforeseen interaction between the sexes which reveals that offspring survival is affected by chemical signals emitted from the females' eggs.

Lemurs match scent of a friend to sound of her voice

20 hours ago

Humans aren't alone in their ability to match a voice to a face—animals such as dogs, horses, crows and monkeys are able to recognize familiar individuals this way too, a growing body of research shows.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jul 09, 2011
Doesn't the capacity of the gut have more to do with size range of prey the predator can feed upon - as seen in deep sea fish? To reach the conclusions of this study wouldn't you have to associate higher fat storage ability with larger guts? Isn't it the fat storage ability that actually provides storage between feedings and not the gut size? Haven't read the study beyond this summary, but the summary doesn't support the headline herein that gut size directly supports fish in "famine." That would be fat storage ability that supports fish during famine - as in all other animals.

More news stories

Japan lawmakers demand continued whaling

Japanese lawmakers on Wednesday demanded the government redesign its "research" whaling programme to circumvent an international court ruling that described the programme as a commercial hunt dressed up as ...

Revealing camouflaged bacteria

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...

Meteorites yield clues to Martian early atmosphere

( —Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks. Their study, published ...

US judge overturns state's abortion law

A federal judge on Wednesday overturned a North Dakota law banning abortions when a fetal heartbeat can be detected, as early as six weeks into pregnancy and before many women know they're pregnant.