Induced spawning of <i>Liza ramada</i> using three different protocols of hormones with respect to their effects on egg quality

Abstract

Two intramuscular injection strategies were performed for females of Liza ramada. The first strategy was applied with two injections; priming dose (CPE, 20 mg per fish). Then, the resolving dose (200 µg/kg of LHRH-a) was given after 24 h later. The second strategy was applied with two injections; the priming dose (3500 IU HCG per fish). Then, the resolving dose (200 µg/kg LHRH-a) was given after 24 h later. The three successful spawning attempts occurred within 3 days when the female received an extra dose of LHRH-a 100 µg/kg (3rd injection) from the second breeding protocol. In both strategies, the males received a single dose of LHRH-a. Ovarian biopsy of hormonal treated and control females were taken at different times after each treatment in order to monitor oocyte development and to determine the time of ovulation, since voluntary spawning was not expected. Measurements of oocyte diameters were carried out at 24 h intervals (0, 24, 48, and 72 h). Diameters of oocytes were measured with a hemacytometer under a light microscope. Mature oocytes with a diameter of 600 ± 50 were more appropriate to injection and spawning. After the injection of the first strategy, the egg diameters ranged from 650 to 680 mm with clear oocyte center and final dose of the resolving dose of the egg diameters were 700 ± 50 mm. After 48 h from the second injection of the first strategy, only one fish spawned. The total number of the spawned eggs ranged from 1 to 1.2 million/fish with no signs of fertilization having a diameter that ranged from 700 to 750 mm. The spawned unfertilized eggs were rounded colourless and transparent. In the second strategy and after the final injection of the resolving dose, the egg diameters were 800±30 µm. After the resolving dose of the first strategy, there was no response of spawning. It showed more successful spawning rather than the first one which showed deformed unfertilized eggs. At the second breeding protocol, fish spawned during the 48 h after the third injection dose. After 48 h, the first three fish were successfully spawned with fertilization rates of 1, 1.8 and 1.6 million eggs/spawn and the percentage of fertilization were 52, 75 and 64%, respectively, but without hatching, and all the fertilized eggs reached the gastrula stage. Control non-injected females were subjected to the same rearing conditions but did not spawn. Two replicate samples of 1 ml of eggs were taken for both control and injected fish. Regarding fatty acids profile, the results reported that the mono-unsaturated fatty acid (MUFA), oleic acid, was highly recorded in the fertilized eggs of the treated females with the second strategy injection while in the first strategy this was not detected except in the unfertilized eggs. The females that was treated with the second strategy injection had more fatty acids particularly the saturated fatty acid, highly unsaturated fatty acid and polyunsaturated fatty acid, (eicosapentaenoic acid (20:5n-3,EPA), docosahexaenoic acid (22:6n-3,DHA) and arachidonic acid (20:4n-6,ARA). The most significant depletions were observed in polyunsaturated fatty acids. Our results suggested that CPE, HCG and LHRH-a promote ovulation and spawning process for both scheduled induction and the frequency of hormone injection influence the fatty acid composition of normal, injected gonad and fertilized eggs of L. ramada in relation to egg quality.

Keyords: Induced spawning, luetunizing hormone releasing hormone analogue (LHRH-a), gonadotropin hormone (HCG), carp pituitary extract, fatty acids, Liza ramada.

African Journal of Biotechnology, Vol 13(40) 4028-4039