The human body cannot synthesize certain fatty acids: these essential fatty acids must be consumed in the diet. Fish and other aquatic foods are known to be the main sources of polyunsaturated fatty acids (PUFA); therefore, humans obtain most of their eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) by consuming fish, aquatic invertebrates, and algae. The increasing demand for fish and the stabilization of marine fish and freshwater landings have contributed to a widening gap between demand and supply for fish and fish products. This leads to a necessity to improve aquaculture production. Fish are the main contributors of n-3 PUFA in the human diet, although there are some interspecific and intraspecific differences in fatty acid profiles. The fatty acid composition of fish differs depending on a variety of factors, including species, diet, as well as environmental factors such as salinity, temperature, season, geographical location, and whether the fish are farmed or wild. In this chapter, information will be provided on fish fatty acids based on their ecology, feeding habits, lipid contents, and environmental conditions where they are harvested.

Abstract.— The effect of restricted feeding on growth, feed efficiency, and body composition was studied in juveniles of gilthead sea bream, Sparus aurata. Juveniles (6.4 g) were stocked into 12 tanks at a density of 16 fish per tank. Four different feeding schedules were tested on triplicate groups of juvenile fish: (1) control fed for 48 d without deprivation, (2) starvation for 1 d and then refed for 2 d (S1), (3) 50% satiation for 2 d and then refed to apparent satiation for 2 d (R2), and (4) 50% satiation for 6 d and then refed to apparent satiation for another 6 d (R6). Results indicated that all fish subjected to cycled restricted feeding regimes were unable to achieve catching up with control group. The specific growth rate of fish in the control was significantly higher than those in S1, R2, and R6, which were not significantly different from each other. Protein efficiency and protein productive value were significantly higher in R2 compared to control, S1, and R6. Fish in R2 had lowest feed conversion ratio (1.12) compared to the control (1.17). Body protein composition in R6 was less than that of the control, S1, and R2, while moisture, lipid, and ash content were not significantly different compared to the control.

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This study was carried out to determine the proximate, fatty acid, cholesterol, mineral and trace element compositions of the rainbow trout (Oncorhynchus mykiss), which is commonly consumed in Turkey. The moisture, protein, lipid and ash contents of the rainbow trout were 71. 65, 19.60, 4.43 and 1.36%, respectively. Total lipids were mainly characterized by low cholesterol levels (35.04 mg/100 g). The composition of fatty acids showed that total monounsaturated fatty acids (35.56%) were the highest, followed by saturated fatty acids (27.65%) and polyunsaturated fatty acids (23.09%). The mineral and trace elements determined were Ca, Na, K, P, Mg, Mn, Zn, Fe, Pb, Hg, As, Cd, Cu, Ni and Co. Among the minerals analyzed, K was the highest followed by Mg, Na, P and Ca. The most abundant trace elements were Co, Cu, Zn followed by Fe, and all trace elements were present in amounts below the limits proposed by the World Health Organization and the Turkish Food Codes for human consumption in the meat of rainbow trout. PRACTICAL APPLICATIONSThis investigation provides practical and useful information on the chemical composition of rainbow trout, which is widely consumed in Turkey. CorrespondingThese results will be important for the fishing industry, nutritionists, investigators for improving processing and marketing. It is also helpful for similar academic studies and to prepare tables of compositions of food. 52M. CELIK ET AL.

Triplicate groups of 20 European sea bass (35 g) were fed five diets in which the added lipid was 100% fish oil (FO), 40% (CSO40), 60% (CSO60), 80% (CSO80) and 100% (CSO100) refined cottonseed oil (CSO), for a period of 120 days. Overall fish growth, feed conversion ratio and protein utilization were unaffected by dietary treatment, but hepatosomatic and visceral fat indexes increased with increasing dietary CSO. Fillet fatty acid composition of total lipids reflected the fatty acids in the test diets. The monounsaturated fatty acids were significantly higher in fillet of fish fed diet FO, CSO40 and CSO60 compared to other treatments while saturated and polyunsaturated fatty acids (PUFA) were not affected by the dietary treatment. Some fatty acids (18:0, 18:1n-9, 20:5n-3 and 22:6n-3) were present in higher concentration in fillet lipid than in the CSO100 dietary lipid indicating accumulation in fillet relative to test diets. Retention of n-3 LC-PUFA within the fillet was increasingly inefficient among fish fed increasing levels of FO. Thus, this study suggests that CSO can be considered as a relatively effective substitute for fish oil in European sea bass (35 g) in terms of growth performances and feed efficiency as far as fish meal is present in the diet.Keywords: Dicentrarchus labrax, linoleic acid, fish oil replacement, aquafeed, vegetable oils. Avrupa Deniz Levreği Yem Formulasyonunda Pamuk Tohumu Yağının Potansiyel olarak Balık Yağına İkamesi ÖzetYirmi adet Avrupa deniz levreği bireyi (35 g) 120 gün boyunca %100 balık yağı (BY), %40 Pamuk Toplama Yağı(PTY40), %60 (PTY60), %80 (PTY80) ve %100 (PTY100) oranlarında rafine edilmiş pamuk tohumu yağı (PTY) ilave edilmiş beş yemle beslenmiştir. Balık büyümesi, yem çevirim oranı ve protein değerlendirme yem uygulamasıyla değişmezken, hepatosomatik ve visseral yağ indeksi yemdeki PTY'nin seviyesiyle artmıştır. Fileto toplam lipit yağ asidi kompozisyonu test yemlerinin yağ asidi kompozisyonuna yansımıştır. BY, PTY40 ve PTY60 ile beslenen bireylerin fileto tekli doymamış yağ asidi miktarı diğer gruplara göre daha yüksek iken doymuş (DYA) ve çoklu doymamış yağ asitleri (ÇDYA) miktarı etkilenmemiştir. Test yemleri göz önüne alındığında, PTY100 grubu bireylerinin fileto yağlarında bazı yağ asitleri (18:0, 18:1n-9, 20:5n-3 ve 22:6n-3) yüksek oranda birikmiştir. Filetodaki uzun zincirli n-3 ÇDYA'lerin birikimi artan balık yağı oranı ile beslenen balıklarda yetersizdir. Bu çalışma, yemlerde balık unu kullanıldığı sürece, büyüme performansı ve yem değerlendirme açısından Avrupa deniz levreği (35 g) için PTY'nin balık yağını ikame edilebileceğini önermektedir.Anahtar Kelimeler: Dicentrarchus labrax, linolenik asit, balık yağı değişimi, yem, bitkisel yağlar.