Fish Size, Vision Skills Explained

Scientists describe molecular underpinnings of salmon size and of fishes’ ability to navigate murky environments in separate studies.

Kerry Grens
Kerry Grens
Nov 5, 2015

WIKIPEDIA, AARON GUSTAFSONThe age—and, therefore, size—of salmon when they mature is controlled by the same gene in males and females, but acts differently in the sexes, scientists reported today (November 5) in Nature. VGLL3 promotes earlier maturation in males and later maturation in females.

The study describes how a single gene can drive sex differences in the optimal form of a trait, in this case, smaller size at maturity for males and larger size for females. “Since different forms of the gene are favored in males and females, natural selection favors both forms being maintained in the population. This leads to the variation in age at maturity being maintained, which promotes the stability and resilience of Atlantic salmon populations,” Jaakko Erkinaro, a coauthor from the Natural Resources Institute Finland, said in a statement.

Examining genetic information from 1,500 salmon, the researchers found two variants of VGLL3, one for early maturity and one for later maturity. Heterozygote fish ended up expressing the phenotype that was most optimal for its sex. “What is really surprising is that salmon that have one of each variant will become larger if the salmon is female, but smaller if it is male,” Kjetil Hindar, research director at the Norwegian Institute for Nature Research (NINA) and coauthor of the study, told Fish Update.

The scientists said the results could potentially improve fisheries management. “The ‘large salmon gene’ could be used to reintroduce individuals more likely to mature later into populations where large salmon once occurred,” Erkinaro said.

In another study, published today in Current Biology, researchers from Washington University School of Medicine discovered an enzyme that enhances zebrafish’s ability to see in the red and infrared—an especially handy sense for poor visibility. “For example, when salmon migrate from the ocean to inland streams, they turn on this enzyme, activating a chemical reaction that shifts the visual system, helping the fish peer more deeply into murky water.” senior author Joseph Corbo said in a statement.

The enzyme, Cyp27c1, works by converting vitamin A1 into vitamin A2, which subsequently shifts the spectral sensitivity of the eye. The researchers also found Cyp27c1 present in the part of the bullfrog eye that peers down into water, but not the part that looks up into air.

“We don't know when in the course of evolution the Cyp27c1 enzyme first acquired the function it has today,” Corbo told Reuters. “However, the fact that the same enzyme is used by both fish and amphibians suggests that this function originated hundreds of millions of years ago.”