Growth<\/span><\/h2>\nThe development of fish dorsal fin muscles is largely unknown, but zebrafish have two distinct musculature regions that appear early in embryogenesis. The caudal fin has muscles in the region of its middle rays, while the anal fin develops them first. The musculature of the dorsal fin develops slightly later than its anal counterpart.<\/p>\n
The abductor and adductor muscles increase in size as the fin grows. They are divided into two layers at 5.6 mm SL, the superficial fibers become smaller and the deep fibers increase in number. The deep fibers insert onto the proximal caudal bones and vertebrae. At 6.4 mm SL, the lateralis superficialis ventralis is visible, connecting the bases of the three dorsal rays. The lateralis superficialis ventralis is the last muscle to develop.<\/p>\n
The dorsal fins of fish increase in size during migration. Young fish migrate with their dorsal fins enlarged, increasing the lateral surface of their bodies to increase drag. A unique set of motor neurons stabilizes the position of the dorsal fins in relation to the body. They activate in antiphase with the trunk muscles and help maintain the dorsal fin in its vertical position.<\/p>\n
The heritability of the first and second dorsal fins was the lowest amongst the three. However, it was significant for the third dorsal fin at recording two. It was important to note that the variance due to common rearing environments was small, but the experimental tank effect increased significantly from recording one to three. In addition, the genetic variance explained only 6% of the total variation of dorsal fin length in the first two weeks, and 36% at the third recording.<\/p>\n
However, fin damage may also affect growth and welfare. The length of the fins and their erosion were measured using digital image analysis. At recording three, the likelihood ratio tests for fin length and fin erosion were highly significant, but only for the second and third dorsal fin. This suggests that SGE may have a different impact on the development of fish dorsal fins than other measurements. While these results do not prove the existence of a causal relationship between SGE and fin length, they are still worth a look.<\/p>\n