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The effect of dietary inclusion of a mixture of microalgae meal (Schizochytrium limacinum and Nannochloropsis oceanica) (1:1 ratio) on growth performance, gene expression, histology and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss) reared in saltwater was investigated. Three experimental extruded diets containing 0%, 9% and 17% of a mixture of microalgae meal were evaluated in triplicate groups during 10‐week bioassay. The results showed that growth performance and feed conversion ratio were significantly reduced by increasing the dietary inclusion of a mixture of microalgae meal. No significant trends were observed with respect to feed intake and relative gene expression of hsp70, scarb1, IL‐12 and myod. Conversely, increasing dietary levels of a mixture of microalgae meal led to a decrease in vacuolar degeneration of hepatocytes. A reduction of 23% on the amount of 20:5n−3 fatty acid in the muscle was found between the fish fed control and the highest level of the microalgae meal blend diets. Nevertheless, 22:6n−3 fatty acid content did not vary among dietary treatments. These results demonstrate that a mixture of microalgae meal has a potential to be included up to 90 g kg−1 within diets for rainbow trout as a sustainable replacement for fish oil.

Omega-3 long-chain polyunsaturated fatty acids (n-3 LC PUFAs) and vitamin D3 are essential components of human nutrition. A regular human diet is highly deficient in n-3 LC PUFAs. Fish like salmon are highly recommended in the human diet as they are a major source of high-value n-3 LC PUFAs and vitamin D3. The levels of these nutrients have been decreasing over the last few years in farmed salmon, whose production urgently needs sustainable sources of these nutrients. The microalga Nannochloropsis gaditana (NG) is known for its naturally high potential for the production of eicosapentaenoic (EPA, 20:5 n-3) fatty acid. A commercial diet for Atlantic salmon was supplemented with 1% and 10% of spray-dried NG grown under controlled conditions for a high EPA content. Salmon were harvested on day 49, following which, boneless and skinless salmon meat was recovered from fish and analyzed for the fatty acid profile, total fat, and vitamin D3. Vitamin D3, EPA, and docosapentaenoic fatty acid (DPA, 22:5 n-3) levels were significantly increased (p < 0.05) by supplementing the basal diet with 10% NG, thus, NG represents a novel, functional, natural ingredient and a sustainable source of n-3 LC-PUFAs that can raise the levels of healthy fats and vitamin D3 in farmed salmon meat.

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A deoxyribonucleic acid (DNA)-dependent DNA polymerase (DNA nucleotidyltransferase) was purified 3,000-fold from the marine Pseuodomonas sp. BAL-31. The molecular weight of the native enzyme was estimated by glycerol gradient sedimentation to be 110,000. The enzyme migrated in sodium dodecyl sulfate-acrylamide gels as a single polypeptide with a molecular weight of 105,000. An absolute requirement for divalent cation was satisfied by Mg2+ or Mn2+ at concentrations of 1 mM. Monovalent cations at concentrations higher than 50 mM showed an inhibitory effect. The polymerase activity was resistant to N-ethylmaleimide and showed a wide pH optimum.

The effects of a Northern-to-Southern Hemisphere shift on the growth and smoking of steelhead (Oncorhynchus my kiss) were monitored by reference to physiological criteria. Eyed eggs were imported from the Alsea River Trout Hatchery, Oregon. USA (latitude 44°N), to the Lake Rupanco Experimental Hatchery in Chile (latitude 41°S). This transfer of eggs resulted in a notable variation in the age and size at which fish smoked. A minimum smoking size of about 10 cm was observed in the first southern spring of life, when fish were 7-8 months old. Fish that did not reach this size smoked in the second spring of life at age 20 months. Based on our current understanding of the effects of environmental variations on smolt physiology, we offer guidelines for increasing the efficiency of smolt production for this anadromous salmonid in the Southern Hemisphere.