UWM Fish Study Could Advance Muscle Growth Research

MILWAUKEE – A study by UWM scientists presents a new “guinea pig” for physiology research – a fish called the giant danio. The giant danio is a larger relative of the well-studied zebrafish, and together the fish may be ideal research subjects for scientists investigating such diverse topics as muscle growth in fish farm species or degenerative muscle diseases in humans.

Peggy Biga and Rick Goetz, scientists at UWM's Great Lakes WATER Institute, analyzed growth in both giant danio and zebrafish as larvae and adult fish.

Their results, first published in June's American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, showed that although closely related, the species exhibit different muscle growth patterns.

Zebrafish exhibit determinate growth, like mammals, which means they reach a finite size as adults. Giant danio show indeterminate growth, like most large fish, which means they continue to grow as adults.

A major difference, says Biga, is indeterminate growers can develop new muscle fibers throughout their life. In contrast, mammals and zebrafish have a fixed number of muscle fibers at birth or soon after, and mainly increase the size of existing fibers.

Biga and Goetz monitored larval giant danio and zebrafish for four weeks after hatching. They measured faster, more efficient growth in giant danio, and more growth due to new muscle fibers. The scientists also analyzed the effects of growth hormone injections on adult fish. They observed a steady growth increase in giant danio, but little response in zebrafish.

Used in comparative studies, scientists might be able to learn how to enhance growth in fish that are raised commercially, see the effects at the molecular level of growth hormones in fish or even inform muscle dystrophy in humans.

The key to answering these questions, however, is the ability to use the genes of one fish to explain the differences in muscle growth in the other. The zebrafish is one of only two fish species (the other is the pufferfish) with a fully sequenced genome. Once the genome – the complete set of genes for a particular organism – has been identified, the functions that individual genes are responsible for can be isolated. Assigning functions to the genes provides a physiological explanation for the different abilities of similar species.

In combination with zebrafish genomic resources, giant danio could reveal genetic controls of indeterminate growth.

Zebrafish have long been a model organism for vertebrate development because they produce large numbers of clear eggs, so scientists can easily observe growing embryos. But their tiny size makes procedures like drawing blood samples or dissecting certain tissues very difficult.

Giant danio are about six inches long as adults, can provide regular blood samples and are just as easy to raise in lab settings as their smaller relatives.

Biga says the next step is determining if the species are alike enough that the zebrafish genome can apply to giant danio. Previous studies have established the fishes' close evolutionary relationship. If their genetics are compatible, giant danio could replace zebrafish in physiology studies that require larger specimens.

Zebrafish and giant danio also have potential to help scientists understand degenerative muscle diseases in humans. Biga says genetic techniques can induce a mutation that causes a similar disease in zebrafish. If the condition can also be induced in giant danio, scientists can compare its effects on different types of muscle growth.

This project was supported by grants from the National Research Initiative and the USDA Cooperative State Research, Education and Extension Service, as well as the UWM Great Lakes WATER Institute.

The Great Lakes WATER ( Wisconsin Aquatic Technology and Environmental Research) Institute's mission is to further understanding of freshwater resources with multidisciplinary research, education and outreach. Find the Great Lakes WATER Institute online at www.glwi.uwm.edu .

###