Environmental and hormonal control of induced spawning in thin-lipped grey mullet, Liza ramada [Risso]

The reproductive cycle can be controlled by either placing the fish in an appropriate environment or by changing the internal regulating factors of the fish with injected hormones or other substances. The present work was designed to determine the suitable environmental and hormonal requirements for induced spawning of thin-lipped grey mullet, reared in freshwater fish farms. The application of a high-potency synthetic analogue of luteinizing hormone-releasing hormone agonists [LHRH-a] and human chorionic gonadotropin [HCG] for inducing the final stages of maturation, ovulation, and spawning in mullets was investigated in ripe spawners, reared in freshwater fish farms, with average egg diameters of 0.600 mm or more, in suitable water temperature and salinity. Two hormonal injection strategies were used. The first involved the use of HCG as a priming injection, followed, 24 h later, by a resolving injection of HCG. The second strategy followed the same time frame but the priming injection was HCG and the resolving injection was luteinizing hormone-releasing hormone agonists alone or in combination with HCG. The use of pregnyl [HCG] as a priming injection at a dose of 20 000 IU/kg body weight, followed by a second injection of 40 000 IU HCG/kg body weight 24 h later proved to be effective in inducing final oocyte maturation, ovulation, and spawning in Liza ramada at 44-50 h after hormonal injection. The optimum water temperature and salinity was 19° and 35%, respectively. Translucent ovulated eggs had coalesced lipid and yolk masses. The fertilized eggs had one or more oil globules gathered in the upper space of the egg. The blastodisc was situated on the bottom side of the floating egg. HCG is very useful for inducing and synchronizing spawning in L. ramada ripe spawners, reared in freshwater fish farms, in combination with suitable environmental factors

effect of mature broodstock origin on the spawning efficiency of grey mullet, Mugil cephalus

Understanding the biochemical composition of good batches of mullet eggs is a beginning of an investigative process that may one day make it easier to distinguish good eggs from undesirable ones. The present study was conducted to investigate the variations, if any, in the reproductive biology and biochemical composition of wild-caught and pond-reared broodstock of Mugil cephalus. Important biochemical constituents [protein, lipids, amino acids and fatty acids] in gonads and freshly spawned eggs of both wild and cultured female broodstock of M. cephalus were analysed. The results showed that the ovarian activity of cultured prespawning females was lower than that of wild females. The activation and fertilization rates of spawned eggs varied between wild and cultivated mullet females. In addition, there was malformation during the embryonic development of fertilized eggs obtained from cultivated females. There was a significant difference in biochemical contents - namely, amino acids and fatty acids - in gonads and spawned eggs between the two stocks, which seems to be due to differences in habitat conditions, mainly salinity and ion concentrations. With such information, we may be able to enhance the survival of mullet eggs through proper control of husbandry practices including environmental parameters, nutrition and methods for spawning

Response of mucous-secreting cells of the gills and intestine to stress during induced spawning of gray mullet, Mugil cephalus

Introduction: An excess of mucus has been observed in the water during induction of mullet spawning. Few data are available on the physiology of mullets during the induced spawning, especially data on the response of mucous-secreting cells in the gills and intestine

Aim of the work: The aims of the present studies were to evaluate the effects of stress on the mucous-secreting cells in the gills and intestine during induced spawning of Mugil cephalus [Teleostei]

Materials and methods: Quantification of possible cell hyperplasia [or depletion] and the chemical composition of the mucous cells during induction of M. cephalus spawning was carried out using histochemical techniques

Results: The majority of mucous cells were concentrated at the edge of the gill filaments. The mucous cell density in the gills was significantly increased during spawning, but it was significantly decreased during preoviposition mortality. However, the mucous cell density in the mucosal layer of the intestine was significantly decreased during spawning and at preoviposition mortality. The size of mucous cells in both the gills and the intestine was significantly decreased during spawning and at preoviposition mortality, whereas its size was significantly increased in the gills after spawning. Two types of glycoproteins [GPs] [acid and neutral] were identified in the mucous cells of the gill and intestine epithelium of M. cephalus. During induction of spawning, the amount of GPs in the mucous cells altered. The amount of each variety of the carbohydrate [intensity of reaction] differed at the different stages during spawning. In general, the secretion of acidic mucous was increased during spawning

Conclusion: The decrease in the GP contents in mucous cells of M. cephalus, as a result of their hypersecretion in response to stress early during handling and acclimation, decreased the production of mucus and reduced its protective role against desiccation of gill and intestine tissue when the ion concentration changed in water during acclimation and induced spawning. This may be considered one of the possible reasons for mortality. Therefore, caution must be exercised not only in acclimation of fish but also in minimization of exposure of fish to stress during induction of spawning

Effect of stress during handling, seawater acclimation, confinement, and induced spawning on plasma ion levels and somatolactin immunoreactivity in mature female thin -lipped gray mullet, Liza ramada

Understanding the physiological picture of fish during the reproductive cycle, seawater acclimation, and induced spawning is of essential value to know the possible reasons of preoviposition mortality and to develop successful hatchery technology. Determination of the effect of different stress factors on hydro-mineral balance as well as changes in somatolactin [SL] immunoreactive cells in mature Liza ramada females. Water chemistry and the different plasma ion levels were measured. Immunocytochemical staining for the sections of the pituitary gland was performed to describe the activity of SL immunoreactive cells. The plasma levels of PO[3-4], Na[+], K[+], Ca[2+], and Mg[2+] showed a slight increase during transportation without anesthesia. The concentrations of these minerals returned to the initial levels by using clove oil [5 mg/I] as anesthetic. However, their levels decreased during seawater acclimation and gradually increased with confinement to reach the initial values. Furthermore, the levels of PO[3-4], Na[+], K[+], Ca[2+], and Mg[2+] were significantly [P