Indeterminate growers increase muscle mass both by recruiting new muscle fibers (hyperplasia) and by increasing the size of the existing muscle fibers (hypertrophy). Many fish species exhibit indeterminate (hyperplastic) growth.
In this first phase of the study, the researchers found that hyperplasia accounts for 67 percent of the giant danio’s muscle growth, compared to the zebrafish in which hyperplasia accounts for only 47 percent of the growth.
Study: Phase II - Adult growth
In the study’s second phase, the researchers applied growth hormone once every three weeks for 17 weeks to adults of both species. The adult danio continued to grow during the 17-week trial and analysis of muscle fibers showed hyperplastic muscle growth.
Adult zebrafish did not exhibit increased growth or hyperplasia in response to growth hormone, suggesting that zebrafish reach a growth plateau similar to mammals and hence exhibit determinate growth. The zebrafish exhibited little hyperplastic growth after the juvenile phase.
This model can be used to investigate muscle wasting diseases such as muscular dystrophy. Other studies have already shown that a condition similar to muscular dystrophy can be experimentally induced in zebrafish. One of the next steps for the researchers is to induce the condition in the giant danio.
“We anticipate that the giant danio will be able to handle the muscular dystrophy better because of their ability to increase muscle,?Biga said. What makes this intriguing is that human embryos exhibit hyperplasia, but then lose that ability after birth, with one exception. When humans injure a muscle, the muscle sends a signal to special cells attached to the muscle fibers, telling these cells to grow and join to adjacent muscle fiber to repair the injury.
There is also an application to fis
Source:American Physiological Society