Growth and Sex Ratio of Octopus Paroctopus Digueti (Perrier & Rochebrune, 1894) in a Wild Population

In Mexico, studies of octopus Paroctopus digueti are scarce, thus the objective of this research is to evaluate some of its biological aspects in Ohuira Bay, Ahome, Sinaloa, Mexico. From autumn 2016 to autumn 2017, a total of 217 organisms of P. digueti were collected, from which 166 were females, 31 ovigerous females and 20 males. The lengths of the mantle (ML), tentacles or arms (AL) and total length (TL) were recorded as well as the total weight (TW) of each organism. The software FiSAT II was used to obtain the growth parameters by mediating seasonal size frequencies. Considering both sexes, the average registered mantle length was 40.31±2.5 mm. For the analysis of ML-TL y ML-AL, the data were adjusted to a linear-type model. For the relationship between ML-TL, the minimum determination coefficient was observed during spring R² = 0.335, and the highest was registered in winter R² = 0.6452. With regards to the allometry coefficient (b), it was different among the 4 climatic seasons. The theoretical ML growth curve showed both sexes of ML_∞= 73.50 mm, K = 1.30 year⁻¹ and t⁰= 0.10. The estimated values from the growth equation revealed faster growth (ML_∞= 63 mm) within the 1.2 years of their lives, reaching a maximum length at 2.5 years of age. The total weight growth curve of P. digueti octopus was formed by an exponential first stage up to six months and the second logarithmic stage from seven months to approximately 1.8 years. In the summer there were slightly lower coefficients and percentages of instantaneous growth coefficients (IGC) for the lengths and total weight of octopus P. digueti. The highest Fulton’s condition index (k) was recorded in winter. The sex ratio was significant in a proportion of 9.85 F:1 M.