Abstract
Our previous work documented significant advancements in steroid-induced progression of oogenesis, demonstrating that co-treatment of female eels with 11-ketotestosterone (11KT) and estradiol-17β (E2) successfully induced uptake of vitellogenin by oocytes. Here we evaluate the effects of this steroid co-treatment on subsequent time to ovulation and egg quality in shortfinned eels artificially matured by hypophysation. Co-treatment with 11KT (1 mg) and E2 (0.2 or 2 mg) significantly reduced time to ovulation and therefore, the amount of pituitary homogenate required, without any detrimental effects on gonadosomatic index, oocyte diameter or the total weight of stripped eggs. E2 treatment resulted in promising increases in fertilization rates. These indicators suggest that co-treatment with 11KT and E2 holds promise for future artificial maturation practices in terms of minimising fish handling and stress, and of reducing the need for expensive pituitary preparations.
Highlights
The reliable production of good quality eggs is a well-known bottleneck plaguing much of the aquaculture industry [1,2,3]
Our recently published work [26] clearly demonstrates the success of the combined pre-treatment in increasing ovarian yolk deposition and progressing oocytes from the early to mid vitellogenic stage in the absence of exogenous gonadotropin. In this follow-up study on the same fish, we evaluate the efficacy of E2 and/or 11KT as pre-treatment on hypophysation-induced artificial maturation in female A. australis
Whilst androgens look to be the main driver reducing the time and amount of SPH required for induced maturation, estrogens could be instrumental for improving egg quality
Summary
The reliable production of good quality eggs is a well-known bottleneck plaguing much of the aquaculture industry [1,2,3]. The well-documented gonadal arrest of captive eels demands that fish must be frequently manipulated with fertility drugs in order to advance oocytes past the early vitellogenic stage. This has been achieved by hypophysation, i.e., injections of either carp or salmon pituitary homogenates (CPH or SPH, respectively) [6,7,8,9,10,11,12,13,14]. Handling is costly in terms of human resources but being removed from the tank and injected under anaesthesia is inherently stressful for the eels This method is typically associated with reduced egg quality
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