Increased androgen receptor expression in muscle tissue contributing to growth increase in androgen-treated Nile tilapia

The aim of this study was to investigate the molecular mechanism behind androgen-induced sex reversal and growth increase in Nile tilapia. Three-day-old mixed-sex tilapia juveniles were treated with differential dose (0, 5, 10, 20, 30 mg/kg diet) and duration (0, 15, 30, 45, 60 days) regimes of 17α-methyltestosterone. Treatment regimes 10, 20, 30 mg/kg-30, 45, 60 days showed ~95% males, while 0 mg/kg-0 days (control) showed ~50% males (P < 0.01). Next, tilapia was cultured for 6 months in cistern and pond culture systems with 17α-methyltestosterone-treated diet (10 mg/kg) for three different durations: 0 days (control), 30 days (30-day-treated), and 180 days (throughout-treated). Fish in pond culture showed significantly higher (P < 0.05) final weight compared with tilapia in cistern culture (235.76, 156.82 g, respectively). Both 30-day-treated and throughout-treated fish showed significantly higher (P < 0.05) final weight, length, daily weight gain, specific growth rate, and muscle protein content compared with control fish. The androgen receptor β mRNA and protein expression levels in both 30-day-treated and throughout-treated fish were significantly higher (~twofolds, P < 0.05) compared with hormone-untreated control males. However, there was not much difference for all these parameters among the two hormone-treated groups. This higher growth probably results from an androgen-induced increased ‘androgen-androgen receptor’ mediated anabolic pathway. Serum testosterone concentration of 30-day-treated fish after 6 months was similar to that of control males (0.9 ng/ml). Moreover, culture of 17α-methyltestosterone-treated monosex tilapia was found beneficial than hormone-untreated mixed-sex tilapia culture for maintenance of natural fish diversity in indigenous water bodies.     

Synthetic and organic mulching and nitrogen effect on winter wheat (Triticum aestivum L.) in a semi-arid environment

Field experiments were conducted in 2002-2003 and 2003-2004 to evaluate the relative performance of synthetic (black polyethylene) and organic (paddy husk and straw) mulches on soil and plant water status vis-a-vis N uptake in wheat in a semi-arid environment of India. Scope of better utilization of soil moisture was documented through all the mulches, especially during initial crop growth stages, when the moisture content was 1-3% higher in mulches. Soil temperature was more moderate under organic mulches. Paddy husk recorded significantly higher plant biomass, while the effect of mulching in enhancing root growth was clearly documented. Organic mulches produced more roots (25 and 40% higher root weight and root length densities compared to no-mulch) in sub-surface (>0.15 m) layers, probably due to greater retention of soil moisture in deeper layers and relatively narrow range of soil temperature changes under these systems. Incremental N dose significantly improved all the plant parameters in both mulch and no-mulch treatments. Grain yield was 13-21% higher under mulch and so with increasing N levels. Nitrogen uptake was higher in organic mulches and also with higher N doses, while polyethylene mulch showed mixed trend. Mulches were effective in reducing 3-11% crop water use and improved its efficiency by 25%. Grain yield and biomass were well-correlated with leaf area index (r = 0.87 and 0.91, respectively) and water use was better correlated with root length than its weight. Results indicated substantial improvement in water and N use efficiency and crop growth in wheat under surface mulching, and the organic mulches, especially rice husk performed better than synthetic mulches.