Identifying possible sources of stress in beaks of paralarvae of Octopus vulgaris Cuvier, 1797 (Cephalopoda: Incirrata)

Octopus vulgaris is a viable candidate for commercial aquaculture, but rearing procedures might stress individuals, possibly resulting in diminished growth and survival and in a distinct deposition pattern of growth increments in the beak. The present study aimed at investigating the relationship between a possible stress source when rearing O. vulgaris paralarvae, handling, and their beak microstructure. Experimental design consisted of blocks without replicates in order to account for light intensity heterogeneity at culture location. Growth and survival were estimated and beaks were extracted from 120 paralarvae. Increments and stress marks were counted in both sides of the interior region of the upper jaw rostrum. Reading precision and total and weekly differences in biometric measurements, beak variables, and light and diet were estimated. Age at first increment deposition coincided with day 1 of experiment, and a 1 deposition rate was confirmed for the experiment duration (15 days). Stress marks were not significantly present in the increment corresponding to the day of stress application. Their presence on other days indicated, however, that handling procedures can cause stress. Nevertheless, it seems that light intensity and diet quantity, and yet possibly other unknown sources, might have also been relevant and confounded the results. Marks can be used as a biomarker for stress, a valuable characteristic given that stress did not seem to significantly affect growth or survival, although the control treatment showed a tendency for higher survival rates. The use of rostrum microstructure analysis was efficient for early stage paralarvae, but could be less effective for older individuals due to erosion and for other cephalopod species due to beak morphological differences. The results herein presented are important for improving rearing conditions for O. vulgaris paralarvae.

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