Fish grow continually throughout their lives and it would seem to be an advantage to grow big as soon as possible, not only to escape predators but also to begin breeding earlier. So why, in that case, do some individuals continue to grow slowly when it would seem to put them at a disadvantage? David McKenzie and his colleagues wondered whether there were costs to rapid growth, and in particular whether fish that grow slower may tolerate starvation better than faster growing individuals (p. ).
Working with a captive population of European sea bass, the team fed the fish for 3 weeks, before fasting them for a further 3 weeks and then repeated the cycle once more while monitoring the fish's weight and calculating their growth rates. They found that the fish that grew most rapidly when fed were the ones that suffered the most weight (mass) loss when deprived of food.
Collecting the fish that lost the least weight and tolerated food deprivation best, and those that grew fastest when food was plentiful, the team compared the fish's physiology to find out if the fish that tolerated food deprivation had a lower metabolic rate and the faster growing individuals had a higher metabolic rate; but they did not. However, the faster growing fish were able to digest meals more rapidly than the slower growing individuals that tolerated fasting well.
The team suspects that the faster growing individuals take a ‘boom and bust’ approach to life, consuming and growing fast to get ahead in times of plenty and putting up with the consequences of their high energy lifestyle when food is scarce. Meanwhile, the smaller individuals grow more slowly because they cannot consume food as rapidly as fast growing individuals, but starvation takes less of a toll on them, presumably because their metabolic costs are lower when food is scarce. So growing slowly may not be such a disadvantage for fish when the food supply is unreliable.
