Effect of Fluoxymesterone on Sex Proportion and Growth Performance of Nile Tilapia (Oreochromis niloticus L.).

Abstract

One of the main problems to be solved in the commercial production of Nile tilapia is the use of large volumes of steroids during the sex reversion process. The precise evaluation of the time after hatching to start the steroid treatment could help reduce its use in the short-term. The main objective of this work was to evaluate the sex proportion and the growth obtained in a mixed population of Nile tilapia fed fluoxymesterone at different days (3, 6, 9, 12, and 15) after hatching. A one-factor experiment was designed, with the day, after hatching, that the fluoxymesterone (5 mg) began to be supplied as factor (3, 6, 9, 12 and 15). Initial stocking density was 0.4 larvae L -1 . All groups were evaluated by triplicate. Steroid treatment finished at day 25 after larvae stocking. Squash technique was used to determine sex proportion at the end of the experiment (45 days). Growth evaluation was performed based on wet weight and total length obtained from each biometry. The results showed the highest percentage of males (92%) in the fish fed fluoxymesterone from day three after hatching. No anabolic effect on growth was observed in any steroidtreated fish. A negative effect on growth was observed after withdrawal of the steroid in the fish that were fed fluoxymesterone for the longest time. These results show that it is necessary to supply the fluoxymesterone prior to the onset of sex differentiation (5-6 days after hatching) to achieve a permanent reversion of the sex differentiation process.

Effect of the combination of fluoxymesterone and a commercial blend of additives on the sex proportion, growth, and survival of Nile tilapia (Oreochromis niloticus) fry

“…However, considering that the lower value of final survival was observed in the group supplemented with only FM at 20 mg per kg, adding the commercial blend might have helped reduce the steroid's negative effects on survival. Although FM is not considered a steroid with strong negative effects (Ramírez-Ochoa et al 2023) on survival, our work showed that at a concentration of 20 mg kg -1 , it caused a decrease in the percentage of survival at the end of the experiment. Several authors have reported in Nile tilapia and its hybrids survival rates lower than those obtained in the present study, ranging from 24 to 83% for fish exposed to 17α-methyltestosterone and similar steroids through feeding (21 to 30 days) (Carranza 1990, Pérez 2002, Pinza-Pinza 2014 or immersions (López et al 2007, Miranda-Cerritos et al 2008, Botero et al 2011.…”

“…At the end of the experiment, a higher growth was observed in the treatments that received the commercial blend or FM compared to that recorded in the control group. Previous reports, in terms of reproduction, sex reversal, and growth effects of FM in Nile tilapia (Moreno-Enríquez et al 2003, Torres-Hernández et al 2010, Ornelas-Luna et al 2017, Trejo-Quezada et al 2021, have concluded that, although it does not have a clear and powerful anabolic effect as 17αmethyltestosterone does (El-Saidy et al 2005, Abdelghany 2010, Hafeez-ur-Rehman et al 2014, Ajiboye et al 2015, Trejo-Quezada et al 2021), FM has shown, in some instances, a positive effect on growth at the end of the sex-reversal process (Manosroi et al 2004, Gutiérrez-Sigueros et al 2018, Ramírez-Ochoa et al 2023. Ramírez-Ochoa et al (2023) reported that FM withdrawal caused a growth depression in Nile tilapia juveniles.…”

“…In the present study, to ensure that the steroid supplied reached an optimal level in the bloodstream before sexual differentiation was initiated, the fry used still had remnants of their yolk sac at the beginning of the experiment, as suggested by Ramírez-Ochoa et al (2023) to guarantee an optimal start of the sex-reversal process. However, in the present work, the percentage of males obtained was low (under 75%) in all the treatments fed the combination of FM and BA.…”

“…The decrease in the intake of FM by ingesting the commercial blend during the critical stage (labile period) of Nile tilapia could have caused the decrease observed in the percentages of males, regardless of the concentration of FM used. During the labile period of Nile tilapia, the fry must increase the steroid levels (in this case, FM) in the bloodstream and keep them elevated during the days that sex reversal is achievable; the reason that for successful masculinization or feminization of Nile tilapia, it is recommended to feed every few hours to maintain adequate levels of the steroid in the bloodstream (El-Greisy & El-Gamal 2012, Alcántar-Vázquez et al 2015, Marín-Ramírez et al 2016, Juárez-Juárez et al 2017, Trejo-Quezada et al 2021, Ramírez-Ochoa et al 2023). Another explanation for the low percentage of males observed in several groups could be the mixing and homogenization of the steroid when adding it to commercial food.…”

“…In recent years, a lot of research effort has been invested in the development of the Nile tilapia's monosex population technology to exploit their benefits for commercial aquaculture (Beardmore et al 2001, Abucay & Mair 2004, Trejo-Quezada et al 2021, Ramírez-Ochoa et al 2023. In parallel, the incorporation of food additives to the commercial culture of Nile tilapia to improve growth, health, and survival is becoming a widespread protocol for producers seeking to increase culture yield (Toyama et al 2000, Cavichiolo et al 2002, Bombardelli et al 2005, de Araújo et al 2018, Rahman et al 2019, Jo-Rivero & Espinoza 2020, Zamora-Vera 2020.…”