Differential gonadal development of grafted and ungrafted specimens of the Calafia mother-of-pearl oyster, Pinctada mazatlanica (Bivalvia: Pteriidae)

Abstract

Summary The present work deals with the existence of differential gonadal development between grafted and ungrafted specimens of the pearl oyster, Pinctada mazatlanica. Oysters were collected as spat and extensively cultured until they were suitable for pearl formation. A mantle allograft was placed within the gonadal tissue and the treated oysters were maintained under the same culture conditions as untreated oysters. After a year of Keshi pearl formation, samples of gonadal tissue, digestive gland, and muscle were excised from each oyster and used for histological and biochemical analyses. The histological examination of gonads was supported with measurements of the oocyte frequency and diameter and the use gonadic and muscle performance indices. For biochemical analyses, the concentration of carbohydrates, proteins, lipids, and triacylglycerides was studied. A two-way ANOVA was applied for differences in the oocyte diameter, index values, and biochemical composition of specimens over time and experimental treatments. All histological and biochemical results showed that grafted oysters achieved greater gonadal performance and were in better reproductive condition than the controls. They presented higher gonadic index values and lower muscle performance index values than untreated specimens. In addition, grafted oysters showed higher concentrations of lipids and triacylglycerides in the gonadal tissue and digestive gland and lower concentrations of proteins in the muscle than ungrafted oysters. Apparently the mantle allograft stimulates redirection of energy flows to reproduction and gonadal development. The muscle and digestive gland (particularly the former) are the main sources for this energy-requiring process. A neuroendocrine control involving the formation of a complex relationship between both mantle and gonadal tissues is suggested. More studies of the histological, histochemical, biochemical, and endocrine composition of mantle of pearl oysters are required to confirm these findings.