Browsing by Author "Fernandes, Ana Daniela Ornelas Sancho"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- Characterization of embryonic development of european cuttlefish (Sepia officinalis)Publication . Fernandes, Ana Daniela Ornelas Sancho; Sykes, António de Vilhena Andrade FerreiraThe increasing cephalopod human seeking as a source of food have been defined it as an aquaculture candidate in the past 20 years. Such have been propelling the cephalopods culturing, such of the European cuttlefish Sepia officinalis. However there are bottlenecks for this species, for instance, at nutritional level. It has been difficult to define a diet with high nutritional value for the cuttlefish and with reasonable costs for the producer. A variety of alternative types of foods have been tried, but these have been showed to be costly and not as good as natural diets. Artificial diets had been unsuccessful within the culturing of cuttlefish This study aimed to characterize the development of digestive tract during embryogenesis of European cuttlefish Sepia officinalis. The external and internal yolk sacs were mainly focused, as well as their nutritional content (using specific stains) and function. Analysis at macroscopical scale (weight and measurements) and microscopical scale (photographs, histology and image analysis) was performed. Eggs were weighed and measured in width and length. Then, these were cut open and embryos were removed from capsule and photographed. The embryos were then kept in formaldehyde. Images were treated and the area of the external yolk sac and the embryo was measured using image J. Histological techniques were performed to characterize the different embryonic stages and external and internal yolk sacs. Changes in the eggs sizes were observed. An initial reduction of the weigh, width and length during the first 10 dpp (days post posture) was observed. Followed by a rapid increase until hatching (p < 0.001). A strong correlation between the weight and width of eggs (R2 = 0.92) was observed. Being suggested as the most viable form of measurements for different studies. The evolution of egg weight was compared with the study of Sykes, et al. (2009). Similar variation was observed (P <0.05), however, in the present study the weight of the eggs was higher. Females at the present study were bigger and laid larger eggs. Both, external yolk sac and the embryo areas, measured with the image J were correlated. As the external yolk sac decreased, and thus consumed, the embryo increased its size. During embryonic development (from 12 day post posture, dpp) there was an inverse relationship between these two factors (p < 0.001, R2 = 0.91). The total area of the embryo (TEA, sum of the yolk sac area and embryo area) was estimated and compared with the weight of the eggs during the same time period. TEA had an almost linear evolution while the weight of the eggs was exponential during embryonic development. Despite the high correlation between these two factors (R2 = 0.68), it was suggested that the water content may be also relevant in this period. Different stages were identified according to the description of Naef (1928). Throughout embryogenesis it was observed the development of various rudimentary organs, such as eyes, arms and tentacles, mantle and its pigmentation. From stages X-XI onwards, the enclosure of the external yolk sac was observed. From the 13 dpp onwards histological images were collected and allowed a more detailed evolution of both yolk sacs. The contents of the sacs were PAS positive, suggesting the presence of polysaccharides. The extra-ectoderm layer (exe) was observed surrounding the external yolk sac, which was positive for Toluidine-O. The outer side of this layer presented cilia that are responsible for molecules diffusion present in the perivitelline fluid (pf). The inner side of the exe was in contact with the perivitelline sinus (ps), which cells appeared to be absorbed or pinocytosis to the yolk sinus (ys). The sacs content was composed of yolk platelets and empty spaces that may be related to the presence of lipids. Similar spaces were also observed in the internal yolk sac but in this structure, agglomeration of yolk droplets were mostly observed. Such droplets could be the early stages of the digestive gland cells of the embryo. A darker layer around the internal yolk sac was observed, which might be its epithelium, where it was noticed some triangular cells. It was suggested that, similarly to other cephalopods, these cells could either be hemocytes reacting to bacteria or either cellular replacement or detoxification. Near hatching, the animals showed some resemblance with the adults and the external yolk sac was greatly reduced.