Abstract:
All male monosex culture in Oreochromis niloticus (ON) has been identified as a means of eliminating problem of stunted somatic growth caused by their prolific breeding habit. Production of all male ON populations through the use of synthetic steroid hormones has generated environmental and public health concerns, hence the need for natural alternatives. Phytochemicals from plants such as Tribulus terrestris (TT) has been reported as potential means of inducing sex reversal in fish. However, the efficacy of TT extracts for production of all male ON needs to be documented. Therefore, the effectiveness of TT extracts for sex reversal and growth enhancement of ON larvae was investigated.
Extracts of TT obtained using ethanol (TTE), ethyl acetate (TTEA), aqueous (TTA100)at1000C and (TTA27) at 270C (room temperature) were assessed quantitatively for phytochemicals. Two extracts with highest saponin and steroid contents were used for the nutritional study. Each extract was added to isonitrogenous diets (Crude Protein 45%) at 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 g/kg while diet supplemented with 0.5mg/kg of 17-α-methyltestosterone (MT) served as control diet. Oreochromis niloticus larvae (n=3150; 0.02±0.001g) were randomly allotted to treatments in triplicates in a 2x7 factorial design. Fish were fed to satiation for 126 days. Percentage males (PM) in randomly selected fish (n=210) were determined using sex-linked markers. Growth performance indices such as Mean Weight Gain (MWG) and Specific Growth Rate (SGR) were determined. Blood (5mL) was sampled to evaluate Haematocrit, Aspartate aminotransferase (AST) and Serum Cholesterol (SC) using standard procedures. Data were analysed using descriptive statistics, ANOVA and Polynomial regression at α0.05.
Flavonoid, saponins, anthraquinones, terpenoids and steroids were present in all TT extracts. Saponin was significantly highest in TTA27 (83±0.0mg/g) while steroid was highest in TTE (19±1.0mg/g). Least saponin (1±0.0mg/g) and steroid (3±0.00mg/g) were obtained in TTEA. Percentage males were 87.62±2.02% and 90.48±2.0% for TTE and TTA27 respectively. Least (53.33±11.6%) and highest (100.00±0.0%) PM were obtained in 0.0g/kg and 1.5g/kg TTA27,respectively. Least (3.56±0.4g; 4.110±0.1%/d) and highest (3.73±0.4g; 4.156±0.1%/d) MWG and SGR were recorded in TTE and TTA27, respectively. The MWG varied significantly from 2.26±0.2g (0.0g/kg) to 4.80±0.2g (2.5g/kg TTA27), while SGR were 3.79±0.1%/d and 4.39±0.03%/d in 0.0g/kg and 2.5g/kg TTA27, respectively. Optimum inclusion level of TTA27 relative to MWG was 2.05g/kg (R2=0.95). Haematocrit ranged from 25.36±0.1% (TTE) to 25.37±0.1% (TTA27) while AST was 64.14±0.1µ/L (TTE) to 64.30±0.1µ/L (TTA27). Highest (25.66±0.01%) and least (25.12±0.02%) haematocrit were recorded in 0.5g/kg TTA27 and 1.0g/kg TTE, respectively. The AST was highest (64.94±0.0µ/L) in 0.0g/kg and least (63.57±0.6µ/L) in 0.5g/kg TTE. The SC ranged from 141.34±0.1g/dL (TTA27) to 142.08±0.1g/dL (TTE). Significantly highest SC (162.60±0.3g/dL) was recorded in MT while 2.5g/kg TTA27 gave the least (134.44±0.16 g/dL).
Tribulus terrestris water extract at 1.5g/kg could optimally reverse sex of Oreochromis niloticus larvae. Diets containing Tribulus terrestris water extracts at inclusion level of 2.05g/kg enhanced growth and health of Oreochromis niloticus larvae.
