Effects of temperature and photoperiod on ovarian recrudescence in the cyprinid fish Mirogrex terrae‐sanctae

Abstract

Mirogrex terrae‐sanctae is a commercial, sardine‐like cyprinid fish in the Sea of Galilee. The fish spawns from December to the end of March. Females collected at the quiescent phase of the cycle (June) were exposed to four combinations of photoperiod and temperature for 3 months. The highest GSI (2.44 ± 0.22) was found in females exposed to simulated winter conditions (16°C, 9L) while the lowest GSI (0.65 ± 0.04) was found in fish exposed to simulated summer conditions (27°C, 14L). The GSI of fish maintained at the unnatural combination of 16°C, 14L (1.30 ± 0.09) did not differ from that of fish maintained at the other unnatural combination of 27°C, 9L (1.07 ± 0.11). However, histological examinations revealed that vitellogenic oocytes were present only in fish maintained at low temperature regimes, which implies that the growth of the ovarian mass in the 27°C, 9L group was due mainly to oogonial proliferation and that vitellogenesis was inhibited in Mirogrex at a high temperature.Both protein and calcium concentrations increased in the serum of fish following injections of oestradiol‐17β. The increase of calcium was evident only in the non‐filtrable (bound) fraction, suggesting that the total serum calcium above 13 mg% could be used as an indirect parameter for circulating vitelloprotein.Fish collected at the quiescent phase were injected with oestradiol (50 μg/fish c. 15 g body weight) and subsequently transferred to tanks maintained at either 12°, 20° or 27°C. The total serum calcium increased to 23.0 ± 1.75 mg% in the fish maintained for 8 days at 20°C. This was significantly higher than the concentration of calcium in the serum of fish maintained at either 12°C (7.8 ± 0.52) or 27°C(l1.8 ± 0.77). This implies that the temperature may affect ovarian recrudescence by modulating the response of the liver to oestrogen, allowing the oestrogen‐induced vitellogenesis to be relatively high in the cool environment during winter.