The Reproductive Biology and Spawning of Zebrafish in Laboratory Settings - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 3

1.2.2 Reproductive Cycle and Controlling Factors

Zebrafish typically attain sexual maturity within 3-6 months post fertilization in
laboratory settings, although this may vary considerably with environmental condi-
tions, most importantly rearing densities, temperature, and food availability (Spence
et al., 2008). Consequently, it may bemore appropriate to relate reproductivematurity
to size rather than age. Data from a number of studies indicate that a standard length of
approximately 23 mm corresponds with attainment of reproductive maturity in this
species (Eaton and Farley, 1974; Spence et al., 2008).
Under favorable conditions, zebrafish spawn continuously upon attainment of
sexual maturation (Breder and Rosen, 1966). Females are capable of spawning on a
daily basis. Eaton and Farley (1974) found that females would spawn once every
1.9 days if continuously housed with a male, and Spence and Smith (2006) reported
that females were capable of producing clutches every day over a period of at least
12 days, though variance in egg productionwas substantial. This interval is likely to be
greater when the environment (water chemistry, nutrition, behavioral setting, etc.) is
suboptimal or if the fish are used for production frequently (Lawrence, 2007).
Olfactory cues play a determining role in zebrafish reproduction and spawning
behavior (Fig. 1.1). The release of steroid glucuronides into the water by males
induces ovulation in females (Chen and Nartinich, 1975; Hurk and Lambesrt, 1983).
Gerlach (2006) reported that females exposed tomale pheromones showed significant
increases in spawning frequencies, clutch size, and egg viability when compared with
females held in isolation. Upon ovulation, females release pheromones that in turn

Ovulation and
pheromone release

Pheromone release

(a) (b)

Male chasing behavior

(c) (d)

Spawning

Figure 1.1 Simplified model of olfactory control of zebrafish reproduction. (a) Male (yellow)
releases pheromone into water in vicinity of female (blue). (b) Female smells pheromone, which triggers
ovulation (indicated by female color change to green), which is then followed by female release of
postovulatory pheromones. (c) Male senses pheromones, which trigger mating and chasing behavior.
(d) Spawning. (See the color version of this figure in Color Plates section.)