the objective of this study was to determine the efficacy of two procedures i.e. feeding and immersion followed by feeding, for masculinizing blue hap. two experiments (experiments i and ii) were conducted. in experiment i, feeding hormonal treatment was applied on post-yolk sac stage fry (10 days after fertilization at 27ºc). dosages of 30mg (group a) and 60mg (group b) of 17α-methyltestostero...

Aquaculture production of cod has decreased from over 20,000 tonnes in 2009 to less than 2,000 tonnes in 2014 and the industry faces many challenges, one of which is high and unpredictably variable mortality rates in the early life stages. Hence, full-cycle farming with hatchery produced juveniles is still considered unprofitable compared to fisheries and on-growing of wild cod. In the present ...

Identification of parasite species is particularly challenging in larval and juvenile hosts, and this hampers the understanding of parasite acquisition in early life. The work described here employs a new combination of methods to identify parasite species and study parasite succession in fry of perch (Perca fluviatilis) from Lake Constance, Germany. Classical morphological diagnostics are comb...

The principal physical mechanism of sound generation is similar in songbirds and humans, despite large differences in their vocal organs. Whereas vocal fold dynamics in the human larynx are well characterized, the vibratory behaviour of the sound-generating labia in the songbird vocal organ, the syrinx, is unknown. We present the first high-speed video records of the intact syrinx during induce...

For studying the effects of different levels of testosterone propionate on growth, survival and sex-ratio, five different doses such as 125, 100, 75, 50, 25 mg hormone per kg feed were administered to 5-day old Clarias gariepinus fry through diet for a period of 40 days. The growth performance in terms of weight and length gain of the fry receiving 100 and 75 mg hormone per kg feed were signifi...

In a previous experiment in which Nile tilapia fry were successfully masculinized, we investigated how the concentration of trenbolone acetate (TA) in the immersion water changed before and after treatment. The results from that experiment indicated that the concentration of TA before and after treatment of Nile tilapia fry was highly variable and below the expected levels. Therefore, we decide...

For over 30 years, the African cichlid fish, Astatotilapia burtoni, has been an important model system for studying the mechanisms underlying socially mediated behavioral change, with the focus being the dominance behavior of males. A recently collected wild-stock (WS) of this species invigorates interest in parallel studies of females' behavior. Here, we describe a robust 'good-mother' phenoty...