An investigation on the effects of serotonin and photoperiod on the reproductive efficiency of freshwater crayfish Pontastacus leptodactylus (Eschscholtz, 1823)

In recent years, crayfish aquaculture industry has been developing rapidly in different regions of the world. Therefore, it is important to know which factors affect reproductive efficiency in crayfish. In the present thesis, the effects of different factors such as water temperature, broodstock size, photoperiod, serotonin injection, and annual cycle on the reproductive efficiency of male Pontastacus leptodactylus (Eschscholtz, 1823) were investigated. The results showed that the spermatophore of P. leptodactylus should be incubated in physiological solution at 23 °C for 4 h to recover the greatest number of extracted spermatozoa (Chapter 2). The results also showed that the high water temperature (19 °C) caused a reduction in sperm production (P < 0.05) (Section 3). Larger than 60 mm P. leptodactylus seems to be more profitable for crayfish hatcheries, considering their higher spermatozoa number (Chapter 4). In addition, constant darkness (0L:24D) caused the highest number of spermatozoa production (1.4 × 107 ± 0.4) and gonadosomatic index value (GSI, 2.8 ± 0.2 %) (P < 0.05) (Chapter 5). In male, the highest spermatozoa number (9.3 × 106 ± 1.2) and hemolymph methyl farnesoate level (0.66 ± 0.06 ng/ml) were observed after the injection of 10 μg of serotonin (P < 0.05) (Chapter 6). However, serotonin injection to females did not significantly affect (P > 0.05) reproductive parameters (Chapter 7). It was also found that serotonin injection caused an increase in the level of hemolymph MF in male P. leptodactylus, but a reduction was observed in the levels of hemolymph MF after the injection of serotonin in female P. leptodactylus (P < 0.05) (Chapter 6 and chapter 7). Moreover, significantly higher spermatozoa number, GSI, testicular index (TI), and vas deferens index (VDI) were recorded in January (P < 0.05) while the hepatosomatic index (HSI) reached the peak in August (P < 0.05). The findings showed that spermatophore degeneration starts in April (Chapter 8). Furthermore, in this thesis, it was found that artificial insemination is possible in P. leptodactylus (Chapter 9). In conclusion, this thesis shows that constant darkness and 10 μg/g body weight of serotonin injection improve the reproductive efficiency of P. leptodactylus.