Histochemical analysis of mucosubstances in oral mucosa of mouthbreeding cichlid fish and seasonal variations in them.

Abstract

The oral mucosa of females of mouth-breeding Tilapia mossambica was studied histochemically to determine the nature of the mucosubstances and to find out variations in them in the seasonal breeding cycle. The mucosubstances exhibited intense reactivity towards all the histochemical methods employed in the breeding season, whereas their reactivity in the nonbreeding period was very weak which increased in the prebreeding period reaching a maximum in breeding period and decreased in postbreeding period. The oral mucosa in the breeding period contained diastase-resistant PAS reactivity, though the amount of diastase-labile reactivity was also appreciable. Acidic groups were detectable due to their stainability by several basic dyes which were utilised singly or in combination. Considerable diversity of the oral mucins was noted in their affinity towards azure A at different pH. At low pH, no metachromasia was apparent which became visible at higher pH. The mucous membrane was reactive towards alcian blue at pH 1 and 2.5, aldehyde fuchsin and exhibited intense and selective alcianophilia in presence of 0.2 M MgCl2. The alcianophilia was partially sialidase-labile, so also was the metachromasia with azure A at pH 3. Hyaluronidase digestion had no effect on alcianophilia and metachromasia. The histochemical staining reactions and their subsequent modifications by enzyme and chemical treatment indicate that the mucosubstances in the oral mucosa contain sulfomucins, sialomucins, and neutral mucosubstances. Such mucosubstances show seasonal variations in their concentration during seasonal breeding-nonbreeding cycle, which seem to be under hormonal control.