Influence of photoperiod over morphometric and hematological parameters of juvenile piracanjubas (Brycon orbygnianus)

Abstract

The aim of this study was to evaluate morphometric and hematological parameters of juveniles Piracanjubas treated with two distinct photoperiod. Twenty nine fish with 100 g, in a factorial design were performed in 18 h light:6 h dark (18L:6D) and 6L:18D two different photoperiod, and morphometric and hematological parameters were evaluated at 45 d and 90 d after photoperiod treatment. Benzocaine 1% was used for euthanasia. Fish were weighed and measured, so as visceral fat, liver and gonads. Hematocrit, total count of white cells, lymphocytes and neutrophils were counted. Results showed that there was no significant relationship between bodyweight and standard length. Significant interaction (P = 0.00018) had been found between the fat index (FI) and gonado-somatic index (GSI) and the photoperiod and time. At 90 d, the fish kept in 18L:6D had a lower rate of fat than the fish kept in 6L:18D (P < 0.05). The GSI was higher in the group 6L:18D compared with the 18L:6D (P < 0.005). There was no interaction between photoperiod and period of treatment for total leukocyte count, however with 90 d, the total leukocyte count was decreased (P < 0.05). Moreover, decrease of the hematocrit from 58.1% to 46.9% and an increase of lymphocytes from 31.5% to 43.5% had been found in fish kept in 18L:6D after 90 d (P < 0.05). Fish kept in 6L:18D presented an increase in segmented neutrophils and lymphocytes (P < 0.05). It is concluded that photoperiod maintained at 6L:18D for Piracanjubas permits a greater gonadal development and an amount of immune cells over the photoperiod maintained in 18L: 6D.