Publication Date:
2021-05-19
Description:
This study was aimed to investigate the effects of different doses of two hormones and an anti-aromatase, i.e. 17 methyl testosterone (MT), methyl di hydrotestosterone (MDHT) or mestanolone and letozole in masculinization of Nile tilapia (Oreochromis niloticus) under the condition of brackish water in Bafgh station situated in Yazd province in center of Iran. Each experiment in this study was consisted of 5 treaments with 3 replicates each. A number of 1725 larvaes was distributed randomly among 15 replicates at the beginning of each experiment. Each experiment lasted 45 days and the larvaes were reared in aerated flow-through pots and fiberglass tanks filled with brackish water. The averages for temperature, salinity, pH and dissolved oxygen of water were 26.9 ê, 8 g/l, 7.6 and 5.78% respectively during this study. In experiment 1, three different doses of 40, 60 and 100 mg MT/k of feed were fed to different groups of 7 day post fertilization (dpf) larvaes for 45 days from the beginning of the experiment. The results showed that the larvaes in 40 mg group were 100 percent masculinized based on squash test performed at the end of the experiment but masculinization rates of those in 60 and 100 mg groups were 99.7 and 96.2 perecent respectively. Based on Dunkan test, total body length and weight averages measured in biometry 3 (at the end of the experiment) were not significantly different among groups but in biometry 2 (30 days after the beginning of experiment), they were significantly lesser only in 40 mg group (P〈0.05). There was significant differences in survival rate of different groups of larvaes in this experiment based on chi-square test (χ=31.166, P〈0.05) and the values in 40 and 100 mg groups (74.5 and 82.9% respectively) were lesser than those in 60 mg, control 1 and control 2 groups (84.3, 89.0 and 87.0 respectively). In experiment 2, masculinization rates of two different groups of larvaes immersed in 1800 µg MDHT/liter once in 10dpf and twice in 10 and 14dpf were 80.0 and 91.9 percent respectively. There were no significant differences in total body length and weight averages measured in biometry 2 between different groups but significant differences were observed in total body length only in biometry 3 (P〈0.05) where the highest values occurred in experiment 1 and control 1 groups and the lowest one in experiment 2. Significant differences observed in survival rate of different groups of larvaes in this experiment based on chi-square test (χ=15.165, P〈0.05) and the rates in experiment 1, control 2 and 3 groups (89.9, 86.4 and 89.9% respectively) were higher than those in experiment 2 and control 1 groups (82.0 and 82.3 respectively). In experiment 3, three different doses of anti-aromatse letrozole (200, 300 and 400 mg/k feed) were fed to different groups of 7 day post fertilization (dpf) larvaes for 45 days from the beginning of the experiment. The larvaes in 400 group .were all masculinized whereas the masculinization rates in 200 and 300 mg groups were 99.0 and 99.6% respectively. There were significant differences in total body length and weight averages measured in biometry 2 and 3 among groups in this experiment (P〈0.05) where the highest and the lowest values occurred in control 2 and experime2 groups respectively. Based on chi-square, the survival rate of different groups was significantly different (χ=41.119, P〈0.05) and the lowest rate occurred in experiment 2 group. No significant differences observed in gender ratios whithin all control groups in this study based on chi-square test. According to the findings aquired under the condition of brackish water at the present study, it would be potentially recommended to use MT and letrozole for the production of all male polpulations of Nile tilapia fish in order to provide fish farmers with no harmful environmental impacts on water sources in rivers and seas which occured due to the uncontroled breeding of tilapia. However, more research is needed to draw firm conclusions to use hormones and in especial anti-aromase letrozole because of the shortage of sufficient data in current references.
Description:
Iranian Fisheries Science Research Institute
Description:
Published
Keywords:
Masculinization
;
Nile tilapia
;
17α-methyl testosterone
;
Methyl di hydro testosterone
;
Mestanolone
;
Body weight gain
;
Total body lenght
;
Brackish water
;
Male
;
Oreochromis niloticus
;
Hormones
;
Temperature
;
Salinity
;
pH
;
Dissolved oxygen
;
Fertilization
;
Survival rate
;
Larvae
;
Investigation
Repository Name:
AquaDocs
Type:
Report
,
Refereed
Format:
61pp.
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