The androgenic and anabolic effects of pine pollen on Nile tilapia (Oreochromis niloticus)

- Abaho, Ivan

Title
The androgenic and anabolic effects of pine pollen on Nile tilapia (Oreochromis niloticus)
Creator
Abaho, Ivan
Subject
Uncatalogued
Date Issued
2023-10-13
Date
2023-10-13
Type
Academic theses
Type
Doctoral theses
Type
text
Identifier
http://hdl.handle.net/10962/431615
Identifier
vital:72790
Identifier
DOI 10.21504/10962/431615
Description
All-male tilapia aquaculture is desirable to control unwanted breeding. Besides, male tilapia individuals grow faster and bigger than females. Presently, most farmers use 17α- methyltestosterone (MT) to produce an all-male stock, although the hormone is associated with human health and environmental risks. Recently, plant-based products have been reported to induce masculinisation in fish and are considered safe nature-based alternatives to MT. The present study utilised pine pollen (PP) to induce female-to-male sex change in Nile tilapia (Oreochromis niloticus). Prior to the start of the research, there was insufficient information on the use of PP for sex inversion, with no published data on the sex change mechanism, hence limiting the progress in the application of the product from experimental to hatchery levels. In this study, the optimal dietary inclusion of PP for maximum masculinisation of Nile tilapia was investigated by feeding three-day-old fish graded PP levels (80, 160, 320, 640, 1,280, 1,920, 2,560 and 3,200 mg kg-1 basal diet) from 3 to 30 days post-hatch (dph). This was compared with fish of the same batch fed the same basal diet with no PP (CT; negative control) or the same basal diet supplemented with 60 mg MT kg-1 (MT; positive control). To confirm whether the sex change was complete, fish in all treatments were fed only a basal diet for an additional 84 days. The associated differences in the growth of the fish were also determined. Pine pollen and MT significantly skewed the expected 50:50 (male: female) ratio towards more male individuals (Chi-square: X2 = 54.396, df = 9, P < 0.001). The 1,280 mg PP kg-1 of diet equally induced masculinisation (80.0 ± 2.9 % males) as MT (89.2 ± 2.2 %), and both were significantly higher than 50.8 ± 2.2 % in the CT treatment. In addition to masculinization, dietary inclusion of 1,280 mg PP kg-1 improved fish growth, with the specific growth rate significantly higher than fish from the MT and CT treatments (One-way ANOVA: F(9, 20) =14.196, P < 0.001). An increment in the dietary levels of PP from 1,280 to 3,200 mg kg-1 further promoted the growth of the fish but did not affect masculinisation. The mechanism underlying PP-induced sex masculinisation was investigated using all-female Nile tilapia fed a basal diet supplemented with 1,280 mg PP kg-1 for 28 days from 3 dph, in comparison with fish fed a basal diet incorporated with 60 mg MT kg-1 (MT treatment) or only a basal diet (CT treatment). The expression of sex-related genes (dmrt1, amh, cyp19a1a, and foxl2), changes in sex steroid profiles (T: testosterone, 11-KT: 11-ketotestosterone, and E2: 17β-estradiol), and gonadal histology were analysed. Gene expression and sex steroid concentrations were significantly influenced by the interaction between dietary treatment and time, with the expression changing differently over time among the treatments (RM-ANOVA: P < 0.001). Pine pollen significantly up-regulated the expression of dmrt1 and amh, while cyp19a1a and foxl2 were down-regulated. Corresponding to male sex gene up-regulation, male-based steroids (11-KT and T) levels were also significantly amplified in both PP and MTtreated fish. The gene expression pattern and changes in sex steroids corresponded to a higher proportion of male individuals obtained in the MT and PP treatments (MT: 97.8 ± 1.1 % and PP: 77.8 ± 2.9 % males), implying female-to-male sex change induction. Subsequently, spermatogonia and spermatocytes were the dominant germ cells in the histological sections of the gonads obtained from the PP-treated fish. At the same time, the individuals from the MT treatment exhibited mainly spermatids and spermatozoa. In contrast, all the fish from the CT treatment remained females, having only ovarian tissues. This thesis confirmed that PP induces female-to-male sex change in Nile tilapia and enhances fish growth. The research contributed novel information on the mechanism underlying PP induced sex change, which included disrupting the expression of sex genes and the androgento- estrogen balance, ultimately determining the sexual fate of the fish. The findings provide a foundation for understanding the role of PP in masculinisation, with broad potential application in the aquaculture industry.
Description
Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
Format
computer
Format
online resource
Format
application/pdf
Format
1 online resource (220 pages)
Format
pdf
Publisher
Rhodes University
Publisher
Faculty of Science, Ichthyology and Fisheries Science
Language
English
Rights
Abaho, Ivan
Rights
Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-ShareAlike" License (http://creativecommons.org/licenses/by-nc-sa/2.0/)
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