Response of mucous-secreting cells of the gills and intestine tostress during induced spawning of gray mullet, Mugil cephalus

IntroductionAn excess of mucus has been observed in the water during induction of mullet spawning.Few data are available on the physiology of mullets during the induced spawning,especially data on the response of mucous-secreting cells in the gills and intestine.Aim of the workThe aims of the present studies were to evaluate the effects of stress on the mucoussecretingcells in the gills and intestine during induced spawning of Mugil cephalus(Teleostei).Materials and methodsQuantification of possible cell hyperplasia (or depletion) and the chemicalcomposition of the mucous cells during induction of M. cephalus spawning wascarried out using histochemical techniques.ResultsThe majority of mucous cells were concentrated at the edge of the gill filaments. Themucous cell density in the gills was significantly increased during spawning, but itwas significantly decreased during preoviposition mortality. However, the mucouscell density in the mucosal layer of the intestine was significantly decreased duringspawning and at preoviposition mortality. The size of mucous cells in both the gillsand the intestine was significantly decreased during spawning and at preovipositionmortality, whereas its size was significantly increased in the gills after spawning. Twotypes of glycoproteins (GPs) (acid and neutral) were identified in the mucous cellsof the gill and intestine epithelium of M. cephalus. During induction of spawning,the amount of GPs in the mucous cells altered. The amount of each variety of thecarbohydrate (intensity of reaction) differed at the different stages during spawning.In general, the secretion of acidic mucous was increased during spawning.ConclusionThe decrease in the GP contents in mucous cells of M. cephalus, as a result of theirhypersecretion in response to stress early during handling and acclimation, decreasedthe production of mucus and reduced its protective role against desiccation of gilland intestine tissue when the ion concentration changed in water during acclimationand induced spawning. This may be considered one of the possible reasons formortality. Therefore, caution must be exercised not only in acclimation of fish but also inminimization of exposure of fish to stress during induction of spawning.