Incorporation of 14C-glycine in the scales of winter flounder (Pseudopleuronectes americanus, walbaum) does not reflect scale growth

Chadwick, Julia Bray (1986) Incorporation of 14C-glycine in the scales of winter flounder (Pseudopleuronectes americanus, walbaum) does not reflect scale growth. Masters thesis, Memorial University of Newfoundland.

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Abstract

The hypothesis that the rate of incorporation of ¹⁴C-labelled glycine into isolated fish scales reflects the instantaneous growth rate of fish (Ottaway and Simkiss 1977a,) was tested for scales of winter flounder (Pseudopleuronectes americanus), a marine fish which has a strongly seasonal biology. -- A seasonal study of ¹⁴C-glycine incorporation into scales of wild fish was conducted over a 22 month period. A separate study of ¹⁴C-glycine incorporation was carried out on laboratory-held fish, which were serially sampled over 17 months. In addition, scale growth was estimated by examining scales from all fish sampled, and measuring the width of the growing edge. Changes in length and weight of serially sampled fish were monitored. -- The seasonal cycles of glycine incorporation into scales did not correlate with cycles of scale growth of wild or serially sampled laboratory fish. The cycles of growth in length and weight observed in the serially sampled fish also did not correlate with the cycle of glycine incorporation rates. Peak ¹⁴C-glycine incorporation rates were observed from late July to September, when annual scale growth was nearly complete in most fish. The peak in ¹⁴C-glycine incorporation occurred about two months after peak rates of increases in length and weight. -- Incorporation into anterior scale portions, which included the growing edge of the scale, accounted for only 16 to 34% of whole scale incorporation. The cycle of incorporation of anterior scales paralleled the cycles of incorporation of the epidermis bearing posterior scale portions and of whole scales, but did not correlate to the cycle of scale growth. -- The clear seasonal cycle in ¹⁴C-glycine incorporation was strongly correlated with seasonal changes in epidermal thickness, which have been correlated to changes in gonad condition (Burton and Fletcher 1983). Peak ¹⁴C-glycine incorporation occurred when the epidermis was thinnest, and processes of regeneration were probably highly active. -- Analysis of incubated scales showed that an average 36% of ¹⁴C-glycine was not incorporated into any other molecules within the scale, and only about 13% of the ¹⁴C-glycine was associated with collagen molecules. There were seasonal variations in the distribution of ¹⁴C in various scale fractions, with more incorporation into larger molecules in summer- and autumn-incubated scales than in winter-incubated scales. The highest level of incorporation of ¹⁴C-glycine into collagen molecules occurred in September, which coincided with the period of epidermal regeneration. -- The seasonal cycle of ¹⁴C-glycine incorporation into scales was also influenced by other factors, though only slightly. Seasonal variations in temperature resulted in a variable O₁₀ of the incorporation rate. Fluctuations in the scale free glycine pool changed the relative concentration of ¹⁴C-glycine within the scale, but did not change the timing of the seasonal cycle of incorporation rates. The effects of inhibitors of protein biosynthesis suggested that micro-organisms may colonize the degenerating epidermis and contribute to ¹⁴C-glycine incorporation rates during summer months. -- This study indicated that the basic hypothesis of Ottaway and Simkiss (1977a) was not valid for winter flounder: the rate of ¹⁴C-glycine incorporation was not correlated with the rate of growth of scales or the rate of growth of the fish. Instead, the seasonal cycle of ¹⁴C-glycine incorporation was correlated to the seasonal cycle of degeneration and regeneration in the epidermis. For winter flounder, ¹⁴C-glycine incorporation into scales seemed to be sensitive to generalized processes of protein metabolism, but was not specifically sensitive to collagen synthesis at the growing edge of scales.

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