Sex Determination in Fishes
Biology 342 Fall 2007
Authors: Candace Kam, Ben Kessler & Xeno Acharya
Mechanism
What is Mechanism?
Mechanism describes the physical structures and processes through which a trait expresses itself in an organism. Anatomy, biochemistry, social structure, and many other concrete elements constitute the mechanism.
Prenatal Temperature
Masculinization of cichlids can be achieved by giving an androgen treatment to the fish. Eckstein and Spira (1965). Estrogen has worked in making female cichlids but it is not as “surefire”. (Clemens and Inslee 1968, Guerrero 1975, Tayamen and Shelton 1978, Nakamura and Iwahashi 1982) The ratio of male to female is increased as temperature increases.
Masculinization of Cichlids
Masculinization of cichlids can be achieved by giving an androgen treatment to the fish. Eckstein and Spira (1965). Estrogen has worked in making female cichlids but it is not as “surefire”. (Clemens and Inslee 1968, Guerrero 1975, Tayamen and Shelton 1978, Nakamura and Iwahashi 1982)
Estrogen levels in the gonads of fish play an important part of development of ovaries. Aromatase activity is increased in temperature sensitive sexual determination during the development of the ovaries. On the other hand inhibiting the action of aromatase actually can make a fish become male even when temperatures are raised at a specific temperature that would under normal circumstances produce female fish.
Aromatase Cytochrome P450
Aromatase Cytochrome P450 has intron sequences that have a lot of variation. This diversity can create a difference in sex determination response since aromatase cytochrome P450 is in charge of producing estrogen. Aromatase Cytochrome P450 works by catalyzing the reaction of changing androgens into estrogens, and thereby feminizing the fish.
Numbers of male and females in six species produced in broods raised at different pH values. (From Rubin, 1985)
| Species | pH | Number of Males | Number of Females | Percent Male | 95% C.I. |
|---|---|---|---|---|---|
| P. pilcher | 5.05 6.10 6.90 |
27 15 6 |
1 14 24 |
96 52 20 |
81.30-99.91 31.30-68.70 7.70-38.56 |
| P. subocellatus | 5.40 7.00 |
41 5 |
5 39 |
89 11 |
77.34-96.32 3.85-23.69 |
| P. taeniatus | 5.50 7.00 |
33 4 |
5 34 |
87 11 |
72.57-95.55 2.97-24.27 |
| A. borelli | 5.80 7.10 |
31 3 |
3 32 |
91 9 |
76.59-98.14 1.81-22.74 |
| A. caucatoides | 5.80 7.10 |
33 5 |
3 34 |
92 13 |
77.89-98.24 4.34-26.72 |
| X. helleri | 6.20 6.20 7.80 7.80 |
28 31 1 0 |
0 0 34 30 |
100 100 3 0 |
87.35-100.00 88.86-100.00 0.06-14.76 0.00-11.57 |
