A novel approach to determine maturity stages in cephalopods by tree decision analysis of measurements of the body and the reproductive system: using Illex argentinus and Enteroctopus megalocyathus as biological models

CRESPI ABRIL, A.C.; GALVÁN, D.; ORTIZ, N.

Ciudad de México

Congreso; Mollusca 2014; 2014

Sociedad de Malacología de México, Asociación Latinoamericana de Malacología, American Malacological Society y Western Society of Malacologists

Determining the maturity condition of cephalopods is crucial for stock assessment and management, but maturity stage assignment by morphochromatic characteristics of the reproductive system is sometimes difficult to conduct in practice. This study provides an observer-independent criteria to classify individuals in maturity stages based on decision tree analysis. A total of 4551 squids (Illex argentinus) and 1447 octopuses (Enteroctopus megalocyathus) from patagonian coast (Argentina) were sampled. Each individual was sexed and assigned to a macroscopic maturity stage defined by maturity scales histologically validated . Also, for each individual the weight of the gonad, accessory glands/ducts, mantle length and total weight were recorded and Maturity and Hayashi's indexes were calculated. Two different models were fitted, one considering all maturity stages and another considering only intermediate maturity stages since these are the most difficult to determine in practice. For I. argentinus, the weights of nidamental gland and oviducts were the most relevant variables to classified individuals among all female stages (misclassification 23%) whilst spermatophoric complex and testis weights were the key variables for males (misclassification 23%). The second model showed that nidamental gland and spermatophoric complex weights were the most relevant variables to classify females (misclassification 19%) and males (misclassification 21%) respectively. For E. megalocyathus, oviducts and ovary weights for females (misclassification 16%) and the terminal organ weight for males (misclassification 18%) were the most relevant variables. The second model, highlighted the same variables, but misclassification improved to 13% for both sexes. In all cases, the frequently used indexes for determining maturity were not relevant. Our results suggest that, these new and simple criteria can be used in the field to determine the maturity condition of individuals of both species. Moreover, three decision analysis would be useful for determine stage of sexual maturity of others cephalopod species.