1997). As in other poikilotherms, it is directly influenced by environmental parameters, particularly by temperature. (Dettlaff et al. 1993; Saat and Veersalu 1996a) ...
J. Appl. Ichthyol. 18 (2002), 271–274 2002 Blackwell Verlag, Berlin ISSN 0175–8659
Received: September 15, 2001 Accepted: May 29, 2002
Duration of synchronous egg cleavage cycles at different temperatures in Siberian sturgeon (Acipenser baerii) By E. Gisbert1 and P. Williot2 1 Lab. Acuicultura, Depto. Biologı´a Animal, Fac. Biologı´a, Universitat de Barcelona, Barcelona, Spain; 2Cemagref, Unite´ de Recherche: Ressources Aquatiques Continentales, Cestas Cedex, France
Summary The duration of synchronous cleavage divisions, equal to the interval between the corresponding mitotic phases of two consecutive cleavage divisions (s0 ), was determined in Siberian sturgeon (Acipenser baerii Brandt) at different water temperatures. The linear relationship between s0 (in minutes) and water temperature (T) was logs0 ¼ 2:79 0:07T ðr ¼ 0:996; P < 0:001Þ for a temperature interval between 8.3 and 12:0 C, while at higher temperatures (13–23.0 C) this relationship was logs0 ¼ 2:09 0:02T ðr ¼ 0:910; P < 0:001Þ. According to s0 values, the range of optimal temperatures for early development of Siberian sturgeon eggs was between 12.5 and 20 C. At temperatures exceeding 20 C; s0 did not decrease and even exhibited a tendency to increase, indicating the upper boundary of optimal temperatures for embryos. Introduction A number of rhythmic processes (biochemical, biophysical, cytological) take place during early embryogenesis in the course of egg cleavage. The duration of a single cycle of these processes is usually equal to the duration of a single cleavage division (Gorodilov 1992). Accordingly, the duration of one mitotic cycle during the period of synchronous cleavage divisions, equal to the interval between the corresponding mitotic phases of two consecutive cleavages, has been shown to be an appropriate unit ðs0 Þ for calculating and for comparing the duration of developmental processes during embryogenesis at different temperatures in species undergoing synchronous cleavage divisions (Dettlaff and Dettlaff 1961; Gorodilov 1996). The first mitotic interval or cytokinesis-1 and the time at which fertilized eggs are exposed to external interventions (e.g. early or late shocking) are important procedures in ploidy manipulations. The timing of shock to effectively suppress the second meiotic division and obtain diploid gynogenetic fish and the duration of cytokinesis-1 can be measured more precisely when s0 units are used rather than age (Shelton and Rothbard 1993; Rubinstein et al. 1997). The predictable relationship between the absolute time of cytokinesis-1 and s0 is species-specific in lower vertebrates (cyclostomes, chrondosteans and teleosts) (Ginsburg and Dettlaff 1991; Rubinstein et al. 1997). As in other poikilotherms, it is directly influenced by environmental parameters, particularly by temperature (Dettlaff et al. 1993; Saat and Veersalu 1996a). The duration of the absolute time of cytokinesis-1 and s0 is empirically determined by direct examinations of zygotic development, conducted at similar temperatures. U.S. Copyright Clearance Centre Code Statement:
In the present study, values of s0 at different temperatures for Siberian sturgeon (Acipenser baerii Brandt) are reported and compared with the rate of development in other acipenserid species and teleost fish. Materials and methods Eggs and sperm were obtained from stripping two 15–16-yearold females and five 13–14-year-old Siberian sturgeon males, which had been injected intramuscularly with carp pituitary homogenate (Williot 1997). After insemination at 13 C (fertilization rates were 85–90%), eggs were distributed in 95 15 mm glass Petri dishes (each containing 75 eggs) and placed in eight temperature-controlled troughs (1:5 0:5 0:10 m; length, width, depth respectively) at various water temperatures: 8.5, 9.5, 11.5, 13.5, 15.0, 17.5, 20.0 and 23.0 ð0:1 CÞ. Fertilized eggs were observed under a dissection microscope at 100 magnification every 2–20 min (depending on water temperature). Water temperature was controlled during observations. The time when developing embryos reached the stages of two and four blastomeres (sI and sII , respectively) was recorded for the same developing embryo of the Petri dish (65–70 eggs per water temperature and female). As the duration of the mitotic cycle in acipenserids equals the interval between the appearance on the animal egg hemisphere surface of the first and second or second and third cleavage furrows (Dettlaff et al. 1993), values of s0 at different temperatures from each female were calculated as ðsII sI Þ and compared statistically by an ANOVA test (Zar 1988). The parameters of s0 ; sI ; sII in relation to water temperature (T ) were computed by linear regression using the following formula Log10 sn ¼ a þ bT ; where T is the temperature in C, a the intercept and b the regression coefficient. The inflexion point of log-transformed lines was determined according to changes in the slope from the regression equation and using the best r squared values as the selection criterion (Kamler 1992; Saat and Veersalu 1996b). Results Eggs of Siberian sturgeon showed normal cleavage within the range of tested temperatures (8.5–23 C). However, the proportions of eggs undergoing normal cleavage at 23 C were drastically reduced ( 0.05). The time interval from insemination to the appearance of the first and second cleavage furrows ðsI ; sII Þ in Siberian sturgeon was between 2.7 and 3.0 s0 , depending on water temperature. The above-mentioned time interval decreased as the water temperature increased from 8.3 to 20.0 C (P < 0.05), while it remained constant at 23 C (P>0.05). At temperatures exceeding 20 C, the s0 did not decrease and even exhibited a tendency to increase (Fig. 1). Using semi-logarithmic coordinates (log sn vs temperature), the exponential curves of s0 ; sI and sII were straightened and according to the best r squared criterion (maximum), each of them was divided into two different lines with an inflexion point between 12 and 13 C (Table 1). Mitotic intervals (s0 ) in minutes at different water temperatures for A. baerii as well as several acipenseriformes and modern teleost species are reported in Table 2. Discussion Dettlaff et al (1987) demonstrated that the duration of different developmental periods in several sturgeon species (e.g. A. gueldenstaedtii, A. ruthenus, A. stellatus and Huso huso) when expressed in fractions of the total duration of embryogenesis, rather than in hours, remained constant at different water temperatures. Accordingly, by dividing the time interval into a particular stage (sn , minutes) at a specific temperature by s0 for that temperature (sn =s0 ), the resultant dimensionless quotient is valid for all normal incubation temperatures. As developmental rates directly depend on mitotic rates, this facilitates comparison between different species. In the abovementioned acipenserid species, the duration of sI may vary between 2.6 and 3.0 s0 . Similarly, the present study revealed
Table 1 The relationship between s0; sI and sII and water temperature calculated by linear regression using semi-logarithmic coordinates for Siberian sturgeon (A. baerii) Temperature sn ( C) s0 sI sII
8.3–12.0 8.3–12.0 8.3–12.0
s0 13.0–23.0 sI 13.0–23.0 sII 13.0–23.0
Intercept a (SE)
Slope b (SE)
r Square
P
4 4 4
0.996 0.990 0.992
