The effect of TGF-β1 on collagen production by cultured trout cardiac fibroblasts. A) Average amount of hydroxyproline, used as a proxy for collagen, produced per cell after 24, 48 and 72 h of TGF-β1 treatment in cell pellets. B) The effect of TGF-β1 or l-ascorbic acid (l-AA) treatment on collagen type 1 deposition in cultured cardiac fibroblasts measured 7 days after treatment using Western blot. In panel A different numbers indicate a significant effect of time on the amount of hydroxyproline produced within control cells (P < 0.05) and different letters indicate a significant effect of time on the amount of hydroxyproline produced per cell in the TGF-β1-treated group (P < 0.05). *Significant effect of TGF-β1 on hydroxyproline concentration between control and TGF-β1-treated cells (P < 0.05). In panel B different numbers indicate a significant differences between values. n = 5 for extracellular matrix (ECM) data, where each n represents a separate cell line established from a single heart from a different fish, and each n contains 8–15 technical replicates. Figure modified from (Johnston and Gillis, 2018).