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Strategie oplozování u ryb s vnějším oplozením
SIDDIQUE, Mohammad Abdul Momin
Morphological properties, species specific differences, development, and function of egg envelopes are of importance for a better understanding of fertilization strategies as well as for captive reproduction. We reviewed morphology and the developmental stages of egg envelopes, mechanism of polyspermy block, and also the role of micropyle and cortical granules in polyspermy block for acipenserid eggs. The structure of the egg envelope is similar among the acipenserids, comprising an external envelope (thecal cells, basal lamina, and follicular epithelium), a five-layered oocyte envelope (adhesive layer, alveolar layer, epilayer, and zona radiata externa and interna) and a layer of oocyte matrix and cortical granules. The development of acipenserid egg envelope within the ovary comprises five stages, with further changes following fertilization. Moreover, we standardized the terminology used to describe the egg membranes which can minimize the confusions and be helpful for future work on acipenserids eggs as well as for other fish species. The sperm to egg ratio (required to fertilize eggs) and effects of pre-incubation of eggs in freshwater before fertilization were studied to standardized fertilization protocols for sterlet Acipenser ruthenus. Pre-incubation time had no effect on fertilization success at 430,000:1 and 43,000:1 sperm to egg ratios, while it was significant at the 4300:1 and 430:1 ratios. The use of adequate experimental suboptimal sperm to egg ratio revealed a positive effect of pre-incubation time, such that at the 430:1 ratio, 0.5 min pre-incubation increased the fertilization rate than 10 min. Transmission electron microscopy showed that pre-incubation of eggs in water for <10 min did not trigger a cortical reaction, suggesting that a low sperm to egg ratio 0.5 to 1 min pre-incubation of eggs in freshwater prior to fertilization can enhance fertilization rate of sterlet (minimally do not change fertilization). The effects of pre-incubation in seawater and the duration of egg receptivity were determined for fresh and over-ripe sea bass eggs. Our results revealed a significant effect of pre-incubation time for both the fresh (P < 0.01) and over-ripe eggs (P < 0.01). The fresh eggs had a higher fertilization success than over-ripe eggs. Fertilization success of eggs significantly declined for both of these treatments after 3 min of pre-incubation clearly indicated that sea bass eggs are able to be fertilized by sperm for up to 3 min after release into seawater. Effects of pre-incubation of eggs and activation medium on the percentage of eyed embryos for Ide Leuciscus idus were examined. At the eyed-egg stage, pre-incubation time was significant for the freshwater activation medium (P < 0.001), such that the percentage of eyed embryos declined across the pre-incubation time gradient. Activating medium had a significant effect on the percentage of eyed embryos for each pre-incubation time (P < 0.05). More precisely, freshwater produced the lowest percentage of eyed embryos at all pre-incubation times, whereas saline water and Woynarovich solution produced the highest percentage of eyed embryos at 0 s and 30 s before incubation. Examination of sperm traits showed no impact of activating medium on computer assisted sperm analysis parameters. Our results suggested that saline water or Woynarovich solution improve fertilization rate in Ide during fertilization. In conclusion, this thesis provides basic knowledge on gamete biology, role of egg receptivity period, effects of pre-incubation of eggs and different activating medium which can be useful to understand the fertilization strategies of different externally fertilizing fishes as well as standardize their fertilization protocol for captive reproduction.
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