نشریه ماهیان دریایی
سال چهارم شماره 2 (پیاپی 5، پاییز و زمستان 1399)

Fish meal is the most important protein source in the marine carnivorous fish diet. The need for this protein source has increased with the increase in aquaculture industry production, reciprocally. During these years, the supply of trash fish to produce fish meal decreased significantly. Reduced access to fishmeal and rising demand, followed by increasing prices, is a challenge to the sustainability and development of the marine fish culture. Accordingly, the study of finding new protein sources for complete or partial replacement of fish meal has become an important issue in the fish nutrition industry. Oilseed meal is one of the plant protein sources with moderate protein content (30 -50%). The use of oilseed meal up to 40% replacement of fish meal has resulted in growth performance, feed and economic efficiency comparable to diets containing fish meal as the main protein source. Decreasing the half level of fish meal in the marine fish diet by using this economical meal reduces the cost of formulated feed. Therefore, the cost of marine fish culture will be reduced, and the possibility of sustainable development of this industry will be provided.

Due to the growing population of the world, the demand for fish is increasing worldwide. It seems unlikely that the increasing demand can be coordinated by increasing harvests of fish from the oceans and natural freshwater as harvesting and productivity in this area is limited. So, aquaculture remains the last hope for providing enough fish for the world, limited by land and water. Specific characteristics of aquatic species such as tolerance to different ploidy levels, external fertilization, relatively short growth period and high volume of extracted gametes have led to further genetic development in aquaculture. Biotechnology can play an essential role in improving aquaculture efficiency. The application of biotechnology to various production systems does not come without its negative effects but even still, the merits far outweigh the associated concerns because the techniques are constantly being developed, thereby reducing the negative impacts thereof. Therefore, there is a need to adopt biotechnological practices if the world is to stand any chance of achieving food security.

Microalgae Dunaliella salina, known as the most important source of beta-carotene production in nature, is a eukaryotic microorganism that has a high tolerance range for fluctuations in environmental conditions such as salinity (0.5-5 M), temperature (20-40 C°) and light (50 to 1500 μmol m-2 s-1). This alga has shown antioxidant, anti-cancer and antimicrobial activity due to their beneficial compounds such as carotenoid pigment, glycerol and unsaturated fatty acids, and are therefore a good candidate for use in the food, pharmaceutical and cosmetic industries. Various companies around the world have become interested in its commercial production and have designed and used several systems for its mass cultivation, including cultivation in outdoor ponds or indoor photo bioreactors. Despite the many biological benefits of this microalgae and the efforts to mass-production of this microalgae, there are still barriers to its commercial and cost-effective production. These challenge are mostly related to downstream production processes including harvesting, drying and oil and commercial pigments extraction.

Sea lice caused serious harm to cultured marine finfish in the world. 54% of copepod infestations in marine fishes associated with outbreaks of sea lice. This parasite caused skin lesions near the head, and high infection can result in fish death. Eleven wild cobia with weight ranging from 0.5 to 3.4 kg were collected from the Persian Gulf and transferred to quarantined tanks at Persian Gulf Mollusks Research Station. The fish were examined for any existence of external parasites by the naked eye. And, caligus were found in nine cobia. The highest caligus density was recorded on the head. Furthermore, this parasite was found on the body surface, operculum, fins (dorsal, pelvic, and pectoral). The maximum and minimum caligus densities were 156 and 41, respectively. Trichlorfon (1 ppm for 60 min) or freshwater (0.5 min) were applied by the bath to kill sea lice. In both methods, the fish tanks were changed.

After being released into the aquatic environment, fish sperm have a limited time to reach the egg, two limiting factors for successful fertilization are the time it takes for the sperm to reach the egg and the other limiting time for the micropile hole to close. Sperm quality is one of the important factors in reproduction, which itself is influenced by various parameters such as motility time, sperm rate, osmolarity, sperm concentration in semen and ATP. In addition, nutritional parameters such as vitamins, minerals and fatty acids are involved in increasing sperm quality. It is very important to study the parameters and factors affecting sperm quality, because reproduction and reproduction of fish is one of the important production links in aquaculture. Also, studies on marine fish are much less than freshwater fish, and research in this area is needed for sustainable aquaculture.