Laboratory Spawning Patterns of Mummichogs, Fundulus heteroclitus (Cyprinodontiformes: Fundulidae)
The common estuarine fish species Fundulus heteroclitus or Mummichog has long been used in ecotoxicological studies; however, their periodic spawning pattern is perceived to limit their use in reproductive bioassays and the availability of sensitive life stages. This study evaluated the lunar periodicity of spawning, egg production, and changes in gonadosomatic index (IG) in the laboratory using wild and F1-generation Mummichogs that originated from three different geographic areas: the northern extreme part of their geographic range (New Brunswick, Canada; 45°N), the middle of the northern subspecies range (Massachusetts, USA; 41°N), and within the southern subspecies range (Virginia, USA; 37°N). Unlike some previous studies of wild and laboratory-held fish, Mummichogs from all locations were continuous spawners over a prolonged period of time (8+ weeks) under laboratory conditions. However, there was greater variance in egg production in smaller fish (≤70 mm total length) compared to larger fish. Our results demonstrate the potential to use Mummichogs consistently in testing protocols due to the absence of lunar spawning in the laboratory, and further suggest that larger fish should be used to optimize the power to interpret results when conducting reproductive bioassays.
Temperature (°C±STDEV) over time in Experiment I.
Egg production over time (expressed as eggs per female per day±SEM; n = 3 fish/sex/tank and 10 tanks/location) for Mummichogs (Fundulus heteroclitus) from different latitudes (NB 45°19′N, MA 41°46′N, VA 37°18′N); • new moon, ○ full moon, gray shaded areas indicate the period around the full moon. MASMALL and VASMALL are laboratory-reared F1; MALARGE, NBLARGE, and NBSMALL are wild caught. Note the change in scale in MASMALL and VASMALL.
Egg production (eggs per female per day±SEM; n = 3 fish/sex/tank and 10 tanks/location) per lunar phase (FQ = first quarter, FM = full moon, LQ = last quarter, NM = new moon) of Mummichogs (Fundulus heteroclitus) from different latitudes (NB 45°19′N, MA 41°46′N, VA 37°18′N). Within each group of Mummichogs, different letters indicate significant differences among dates (repeated measures ANOVA, followed by a Tukey's HSD test, α = 0.05). MASMALL and VASMALL are laboratory-reared F1; MALARGE, NBLARGE, and NBSMALL are wild caught. Note the change in scale in MASMALL and VASMALL.
A simulated (A) semi-lunar, (B) lunar, and (C) actual egg production (n = 3 fish/sex/tank and 10 tanks/location) of Mummichogs (Fundulus heteroclitus) from different latitudes (NB 45°19′N, MA 41°46′N, VA 37°18′N) plotted on a radar axis where day is expressed as the angle θ and Y is the distance from the origin; 
last quarter, • new moon, 
first quarter, ○ full moon. MASMALL and VASMALL are laboratory-reared F1; MALARGE, NBLARGE, and NBSMALL are wild caught. Statistical analyses were performed using the residuals from the regression model between log egg production and temperature to adjust for temperature changes over the duration of the exposure.
Gonad size relative to body size (gonadal somatic index, IG [%±SEM]; n = 6 fish/sex/tank and 6–10 tanks/location) for female and male Mummichogs (Fundulus heteroclitus) from different latitudes (NB 45°19′N, MA 41°46′N, VA 37°18′N); • new moon, ○ full moon; different letters indicate significant differences among dates (ANCOVA, followed by a Tukey's HSD test, α = 0.05). MASMALL and VASMALL are laboratory-reared F1; MALARGE, NBLARGE, and NBSMALL are wild caught.
The percent of mature oocytes (eggs > 2 mm [Kneib and Stiven, 1978]; n = 6 fish/sex/tank and 6–10 tanks/location) in the ovaries of mature female Mummichogs (Fundulus heteroclitus) from different latitudes (NB 45°19′N, MA 41°46′N, VA 37°18′N); • new moon, ○ full moon. MASMALL and VASMALL are laboratory-reared F1; MALARGE, NBLARGE, and NBSMALL are wild caught.
Contributor Notes
Associate Editor: D. Buth.