Desarrollo morfológico del apéndice masculino del camarón de agua dulce Macrobrachium caementarius (Molina, 1782)

This study aimed to describe the morphological development of the appendix masculina of the freshwater prawn Macrobrachium caementarius. Freshwater prawns were collected in the Lacramarca River (Ancash, Peru). Fifty-six individuals ranging from 13 to 32 mm total length were analyzed. Each prawn was subjected to cold shock for immobilization and euthanasia. The second pair of pleopods from each individual was dissected and kept in a physiological solution and immediately described. The development of the appendix masculina in the endopodite of the second pair of pleopods allowed us to differentiate six distinct morphological stages. Stage 0 includes sexually undifferentiated individuals. In Stage I it appears as a bud. In Stage II the bud starts to grow. In Stage III the apical spines are visible. Stage IV has subapical spines. In Stage V the appendix masculina is fully developed. Prawn individuals whose size was < 16.21 mm total length did not have an appendix masculina (Stage 0), while those between 16.21 mm (Stage I) to 21.60 mm (Stage V) total length were differentiated as male prawns. The growth of the appendix masculina until full development increased linearly with the total length of the prawn. Prawn individuals with total length ≥ 16.21 mm that did not show an observable appendix masculina were considered as female individuals. The postlarva differs from the juvenile and the latter from the adult (non-functional) by the development of the appendix masculina and by the size of the animal.