Morphological and physiological changes of Octopus bimaculoides: From embryo to juvenile

Octopus bimaculoides is a holobenthic species with fishery importance in Mexico and aquaculture potential because of its high growth rate and direct development from embryo to juvenile, which increases survival in captivity. In cephalopods, transition from yolk utilization to independent active feeding is considered a critical period. Information about the digestive physiology ontogeny of O. bimaculoides is needed to determine the digestive capacity and to improve feed and feeding protocols in captivity for early life stages. Thus, this study assessed changes in morphological and digestive enzymatic activities, as well as biochemical composition of embryos and hatchlings. Internal and external yolk areas and total, mantle and arm lengths were measured in embryos; total wet weight was measured in hatchlings. Activities of lipase, acidic phosphatase, trypsin and chymotrypsin were determined by fluorometric techniques; total lipid, triglyceride and soluble protein concentrations were biochemically measured. Embryonic development lasted around 65 days at an incubation temperature of 18 °C. Embryos grew exponentially while external yolk decreased linearly throughout the embryonic developmental stages. Hatchlings grew exponentially the first 14 days after hatching (DAH). Enzymatic activities were evident since embryo stages, mainly at final development stages. Higher activities of acidic phosphatases and lipases in embryos were detected after the end of organogenesis; while trypsin and chymotrypsin activities, only were at final stages detected previous to hatching. In hatchlings, acidic phosphatase and lipase activities increased the first 12 and 20 DAH, respectively, and protease activities were erratic the first 30 DAH. Lipid concentrations did not show variations in embryo stages but decreased the first 10 DAH. Triglycerides increased in last embryo stages and decreased the first 14 DAH. Soluble proteins decreased in the last embryo stages and in the first 10 DAH. The results of lipases, acidic phosphatases, as well as lipid, triglyceride and soluble protein contents suggested that embryos started to mobilise reserves from the external to internal yolk sac at final developmental stages, and hatchlings were consuming their reserves during the first 10-14 DAH. Protease activity showed that the digestive gland started secretory activity from late embryo stages but continued maturation even after hatching. The results showed that in late embryonic development stages and first days after hatching, enzymatic activity and biochemical components respond to the mobilisation, accumulation and use of yolk reserves in O. bimaculoides.