Automated analysis of spontaneous motor activity in the embryonic zebrafish, Danio rerio

We have developed simple procedures using relatively inexpensive equipment to quantify the early behavior of the embryonic zebrafish, Danio rerio. The early behavior consists of simple myotomal contractions that generate frequent side-to-side thrashing movements within the chorion. These movements are concurrent with the outgrowth of the earliest primary neurons in the zebrafish nervous system. The rate of these movements changes in a relatively consistent pattern over time that almost certainly reflects ongoing changes in the organization of the nervous system. The first observable muscle contractions occurred at 18.3 ± 0.7 hours postfertilization (hr). At first, these movements are slow and sporadic, occurring only 2-4 times/minute. Within an hour, though, they rapidly increase in frequency to a peak of approximately 22±4 twitches/min. Thereafter, the rate very steadily declines by roughly 1.5 twitches/min/hr, flattening out at a slow 1-2 twitches/min after 32 hr. The magnitude of these contractions also increases steadily between 18 hr and 25 hr, as a consequence of the increasing length of the tail, addition of more myotomes, and maturation of muscle fibers.