Damien Desprez

Effect of ambient water temperature on sex determinism in the blue tilapia Oreochromis aureus

Fry from six egg batches of Oreochromis aureus were reared at 21°C (40 days), 27°C and 34°C (25 days) then at 27°C and sexed. High temperature regimes produced high male ratios (mean male percentage: 97.8%) while intermediate thermal regime gave balanced ratios (mean male percentage: 63.0%). Low temperature delayed the differentiation of gonads. Perspectives of using high temperature for the production of monosex populations are discussed.

Production of a high percentage of male offspring with a natural androgen, 11β-hydroxyandrostenedione (11βOHA4), in Florida red tilapia

Abstract This paper reports the effects of a natural androgen, 11β-hydroxyandrostenedione (11βOHA4), on sex-reversed fry of the Florida red tilapia. In a first approach, the optimal dosage and duration were determined in the laboratory. The sex-reversal treatment was applied on post-yolksac stage fry (10 days after fertilisation at 27 °C). Dosages of 20, 30, 40 and 50 mg of 11βOHA4 kg −1 of food were used during periods ranging from 10 to 35 days. Dosages of 40 or 50 mg of 11βOHA4 kg −1 of food during 21–35 days significantly increased the male percentage in sex-reversed groups in comparison to control groups. A lower but still significant deviation of the male percentage was observed when a dosage of 40 mg kg −1 was given during at least 28 days. Lower dosages did not significantly affect the sex ratio of treated groups. Based on the results of these observations, a follow-up study was conducted to evaluate the efficiency of this natural androgen for an intensive production of sex-reversed fry. Optimal dosage (50 mg kg −1 ) and treatment duration (28 days) were applied to increasing stocking density of fry (8000–11,000 fish m −2 ), producing a mean male percentage of 99.1% on the 510,000 treated fry. This study demonstrates the masculinizing efficiency of 11βOHA4 in Florida red tilapia. Interest of a natural androgen, used in sex-reversal treatment, is discussed, particularly for the Florida red tilapia strain.

Production of a high percentage of male offspring with 17α-ethynylestradiol sex-reversed Oreochromis aureus. II. Comparative reproductive biology of females and F2 pseudofemales and large-scale production of male progeny

Abstract In Oreochromis aureus, the use of pseudofemale spawners (sex-reversed male with a female phenotype) is an alternative technique for producing monosex genetically male tilapia offspring. This study compared the reproductive capacities of F2 pseudofemales and females and evaluated the possibilities of applying this process of high percentage of male production on a large scale in earthen ponds. The percentage of non-spawning pseudofemales F2 (40%) is high in comparison to females (20%). On average females spawned three times and pseudofemales spawned once and a significant variation was observed in the frequency of spawning (P 0.05) to that of females (respectively 1668 ± 1445 and 1643 ± 1070 eggs · kg−1 per spawning). The GSI of spawning females and pseudofemales was respectively 3.7 ± 1.7% and 4.4 ± 2.2% (P>0,05). The sex ratio of progeny of pseudofemales deviated significantly (P

Influence du génotype sexuel sur les caractéristiques de la reproduction de femelles (génotype WZ) et de pseudofemelles (génotype ZZ) chez le tilapia Oreochromis aureus

Abstract The sex reversal of Oreochromis aureus (male genotype: ZZ ; female genotype: WZ) with an oestrogen (17α-ethynylestradiol) treatment produces pseudofemales with a male genotype (ZZ). Crossing these fish with normal males (ZZ) gives, in theory, 100 % male offspring. We have determined and compared the principal traits of reproductive biology of three broodstock batches of O. aureus. First batch (batch 1) was constituted using normal females only, the second (batch 2) involved pseudofemales only, while the third batch (batch 3) contained both females and pseudofemales. Fecundity and mean egg weight was not significantly different in females and pseudofemales. In the third group, spawning rate of the pseudofemales (0.6 spawns) was lower than that of the females (6.4 spawning). In this last group, 60 % of the pseudofemales never reproduced. In batches 1 and 2, there were no differences between females (6.9 spawns) and pseudofemales (4.7 spawns). Lowest spawning rate of pseudofemales may result from the expression of the male sexual genotype of these fish.

Inheritance of sex in two ZZ pseudofemale lines of tilapia Oreochromis aureus

Abstract This paper reports a study on the sex determination system of the blue tilapia, Oreochromis aureus . Investigations were carried out using a pseudofemale line in two populations of O. aureus , known as Egyptian Population (EP) and Israel Population (IP). In O. aureus , males are the homogametic sex (ZZ/ZW), and sex reversal of fry with estradiol results in the production of some functional sex-reversed fish with a female phenotype and ZZ male genotype, known as pseudofemales or Δ-females. Crosses between ZZ pseudofemales and ZZ males theoretically should provide monosex ZZ male progeny only. We have studied the sex ratios of progeny from 43 IP (F 2 to F 3 generations) and 51 EP (F 1 to F 5 generations), pair-matings between normal males and pseudofemales. In IP, the male percentage in progenies ranged between 83% to 100% in F 2 and 66% to 100% in F 3 . In EP, male percentage was more constant, varying from 88% to 100% in F 1 , from 96% to 100% in F 3 and from 97% to 100% in F 5 . In EP, F 2 and F 4 pseudofemales produced only monosex male progeny. This apparent difference in sex ratio frequency distributions between the two O. aureus pseudofemale lines could be due to the selection of males. EP pseudofemales were mated with their siblings for F 2 and F 3 pseudofemales or with closely related males for F 4 and F 5 pseudofemales. Conversely, IP pseudofemales were crossed with nonrelated males originating from research center broodstock, resulting in a higher proportion of females in sex ratio of progenies from successive generations of pseudofemales. The role of inbreeding is discussed in the context of predominantly monofactorial sex chromosome determination system operating in this species, influenced by other factors (genetic and environmental). The present study also shows that it is possible to fix the male sex determining factors (Z sex chromosome and genetic factors) in a line of pseudofemales, producing a high percentage of male progeny in five successive generations.

Influence of sexual genotype on the behaviour of females (genotype WZ) and pseudofemales (genotype ZZ) in the tilapia Oreochromis aureus

α-ethynylestradiol sex-reversed males of Oreochromis aureus(pseudofemales, ∆F, genotype ZZ) are used in aquaculture to produce a male monosex population by crossing with ZZ homogametic normal males. When placed with males (M) and females (F) in the same spawning tank, the spawning rate of F is higher than for ∆F. In order to understand this phenomenon, comparisons were made between the behaviour of 18 F (446 ± 96 mm) and 18 ∆F (401 ± 59 mm). ∆F showed a more aggressive behaviour and were significantly more dominant than normal F in fighting pair experiments (F × ∆F) or in fighting group experiments in four different stocking densities (8, 12, 16 and 83 fish 10 -3 l with F/∆F ratio = 1). ∆F were also more aggressive towards males than F were. The results support the idea that behavioural differences exist between F and ∆F. These differences are probably due to the effect of the sexual genotype on behaviour.