Ahmet Adem Tekinay

Effect of dietary Ulva and Spirulina on weight loss and body composition of rainbow trout, Oncorhynchus mykiss (Walbaum), during a starvation period.

A study was conducted to determine the effect of dietary algal supplementation on weight loss and proximate composition in rainbow trout, Oncorhynchus mykiss, during starvation. An algae-free control diet (C) and four experimental diets, including varying levels of raw Ulva meal (5% = U5; 10% = U10) and Spirulina meal (5% = S5; 10% = S10) were formulated. Fish were fed to satiation for 12 weeks and then subjected to a 3-week starvation period. Body weight, viscerosomatic index (VSI, %), hepatosomatic index (HSI, %), dress-out (DO, %) and chemical composition of carcass were analysed at the end of each starvation week. The accumulated weight loss of the fish fed dietary algae was almost 50% less than the control group (p < 0.05) after 2 and 3 weeks starvation. No significant differences in weight loss were observed among the fish fed different algal diets during the starvation period. Total body protein and ash contents remained constant in all groups throughout the starvation period. Fish in all treatments lost a significant level of total lipids and changes of liver fatty acid profiles were also observed. Results indicate that low level inclusion of algae in aquafeeds may have economical advantages in terms of reducing weight loss in fish when subjected to a short-term fasting period, that sometimes is necessary after a heavy rainfall or when fish stocks are held back to meet market demand.

Hazelnut meal in diets for seawater farmed rainbow trout (Oncorhynchus mykiss): effects on growth performance and body composition

Abstract A 77-day feeding trial was designed in order to assess the effect of partial or total replacement of soybean meal by hazelnut meal (HNM) on feed intake, growth performance, nutrient utilization and body composition of rainbow trout (initial mean body weight: 80.0±3.5 g) in seawater conditions. A control and three experimental diets were formulated in which soybean meal level (25.5%) in the control diet was replaced by hazelnut meal at 39.2 (HN 39), 78.4 (HN 78) and 100% (HN 100) to provide 44% crude protein and 20% crude lipid diets. Diets were fed to 125 rainbow trout to apparent satiation by hand twice daily at 09.00 and 16.00 hours under natural photoperiod conditions. At the end of the feeding trial, fish of all groups almost tripled their body weight and no significant difference (P>0.05) was revealed in final weight or specific growth rate between treatments. However, feed conversion ratio (FCR) of the HN100 group was significantly higher than other treatments (P<0.05). There was a slightly decreasing trend in protein efficiency ratio (PER) and net protein utilization (NPU) with increasing level of dietary hazelnut meal, but it was only significant in groups of fish fed HN100. All groups of fish displayed similar carcass and muscle compositions. According to the results of the present study, it can be stated that hazelnut meal can replace soybean meal at up to 200 g kg-1 in grow-out diets of rainbow trout without any detrimental effects on growth performance.