# Comparative Tissue Responses of Marine Mollusks on Seasonal Changes in the Northern Adriatic Sea
## 4 Discussion
Mollusks exhibit cycles of energy storage and utilization in relation to yearly seasons and cycles of gametogenesis. Changes in biochemical tissue composition, thus, demonstrate which of these substrates act in energy metabolism in different conditions. Therefore, gonadal development is followed by a decrease of GLU in muscle, and a decrease of GLU and TRIG in the scallop digestive gland [38]. Histological analysis of scallop and ormer gonads revealed two peaks of gonadal maturation and spawning during the spring/summer and winter seasons for scallops, and one peak during fall for ormers. Spawning is an energy-demanding process and most of the energy comes from metabolism of fats stored in the digestive gland [39]. Therefore, this process could add to the production of antioxidants and TBARS in scallop and ormer gonads in order to protect fatty acids and yolk from lipoperoxidative damage [40]. Another possible reason for the discrepancy in antioxidative status in the two species could be due to species' physiological differences. It was found that the size and number of lipid vacuoles of tubuloacinar terminations in the digestive gland differ between the two species after the microscopic examination, in scallop being several-fold larger in size and number. Similar observations relating to increased fatty acid levels of European oyster (_Ostrea edulis_) tissues in winter were established previously [41]. Both the decreases and increases of temperature suppress the immunity of abalone (_Haliotis discus hannai_) and entice higher ROS production [42]. Interestingly, in this work, ormers had elevated total antioxidant status in the warmer period, which can be attributed to the availability of food containing antioxidant compounds. In scallops, GPx had a peak in June, comparable with the work of [PERSON] et al. [27], where it decreased from fall to winter, subsequently increasing in spring/summer conditions. In scallops, a relationship of increased antioxidant levels (GPx) and decreased lipid peroxidation levels measured as TBARS was evident in June, suggesting that increases in antioxidant enzyme activities could have been responsible for reducing the lipid peroxidation during the temperature increase [15]. Additionally, the feeding pattern of scallops may have an impact on elevated GPx levels in June, as they ingest relatively large phytoplankton particles [43]. Ormers, on the other hand, browse on a variety of seaweeds, but mostly on macroalgae such as Chlorophyta, Rhodophyta and Phaeophyta [44]. In the spring/summer sampling period, salinity reached its minimum of 30.88 psu. Lower salinity might have contributed to oxyradical production in the observed species, particularly ormers, which are not able to tolerate decreased salinity over a prolonged period [3]. However, the Northern Adriatic is a two-layer sea where the surface layer is enriched with a riverine fresher water, while the bottom layer consists of saltier water, and in warmer months particularly, the stratification of the water column is evident [45]. In conclusion, the results suggest that in both species, the environmental conditions and the reproductive period appear to be the main processes influencing the seasonal patterns in their biochemical parameters and tissue morphology. Both species had similar trends in biochemical and antioxidant defense parameters over the seasons, generally with a greater distribution of data in scallop tissues, except in fall. During cold months, a decline in enzymatic antioxidant defense in both species was noted, accompanied by the lipid peroxidation levels decrease in ormers only. Both species demonstrated a season-induced variation in the occurrence of different gonadal stages. The majority of investigated scallops were in the ripe or partially spawned stages in the spring/summer season. In ormers in the spring/summer season, gonads were in the mid-maturation stage, while in fall they were in the ripe or spawned stages.