The Digestive System of the Greater Weever (Trachinus draco L.) as a Potential Alternative Source of Collagen: A Preliminary Study

This preliminary study characterises type I collagen in the digestive system of the greater weever (Trachinus draco L.) by integrating histochemical and biochemical techniques. To the best of our knowledge, this study represents the first baseline mapping of type I collagen within the gastrointestinal tract of this species. Mallory staining and indirect immunofluorescence confirmed collagen presence across the oesophagus, stomach, and intestine. The histochemical quantification of the fluorescent area (100 measurements per organ across 15 fish specimens) showed no significant differences (p = 0.1315), indicating a uniform spatial distribution. However, biochemical analysis via hydroxyproline assay and a two-way ANOVA revealed significant differences in collagen content among organs (p = 0.0308). The stomach yielded the highest concentration (4.199 µg/mg), significantly exceeding that of the intestine (1.713 µg/mg; Šídák’s post hoc, p = 0.0300). This discrepancy suggests that the higher gastric content is due to greater fibre density rather than distribution area. SDS-PAGE and Western blot confirmed protein molecular weights of 100–130 kDa, corresponding to α1 and α2 chains typical of type I collagen. The combination of these histochemical and biochemical methods effectively detects and characterises collagen in fish gastrointestinal by-products. By introducing T. draco as a novel subject in this context, these findings provide essential baseline anatomical and histological data and offer a clear scientific justification for the biotechnological valorisation of unutilised commercial fishing by-products, fully aligning with sustainable marine circular economy principles.