Effects of organic plant oils and role of oxidation on nutrient utilization in juvenile rainbow trout (Oncorhynchus mykiss).

Producing organic fish diets requires that the use of both fishmeal and fish oil (FO) be minimized and replaced by sustainable, organic sources. The purpose of the present study was to replace FO with organic oils and evaluate the effects on feed intake, feed conversion ratio (FCR), daily specific growth rate (SGR) and nutrient digestibility in diets in which fishmeal protein was partly substituted by organic plant protein concentrates. It is prohibited to add antioxidants to organic oils, and therefore the effects of force-oxidizing the oils (including FO) on feed intake and nutrient digestibility was furthermore examined. Four organic oils with either a relatively high or low content of polyunsaturated fatty acids were considered: linseed oil, rapeseed oil, sunflower oil and grapeseed oil. Substituting FO with organic oils did not affect feed intake (P > 0.05), FCR or SGR (P > 0.05) despite very different dietary fatty acid profiles. All organic plant oils had a positive effect on apparent lipid digestibility compared with the FO diet (P < 0.05), whereas there were no effects on the apparent digestibility of other macronutrients when compared with the FO diet (P > 0.05). Organic vegetable oils did not undergo auto-oxidation as opposed to the FO, and the FO diet consequently had a significantly negative effect on the apparent lipid digestibility. Feed intake was not affected by oxidation of any oils. In conclusion, the study demonstrated that it is possible to fully substitute FO with plant-based organic oils without negatively affecting nutrient digestibility and growth performance. Furthermore, plant-based organic oils are less likely to oxidize than FOs, prolonging the shelf life of such organic diets.

Oxygen binding properties of hemoglobins from antarctic fishes.

1. The half-saturation value, P50, for 'stripped' hemoglobins from Trematomus spp. (fam. Nototheniidae) at pH 8.27 and -1.8 degrees C varied from 12.1 mmHg in the pelagic species T. borchgrevinki to 1.3 mmHg in the sedentary benthic species T. centronotus. 2. The nototheniid hemoglobins showed appreciable Bohr effects (phi = delta log P50/delta pH = -0.87 to -0.48) while the hemoglobin from a bathydraconid species, Gymnodraco acuticeps, was insensitive to pH; phi = -0.02 No Root shifts were detected. 3. Cooperative oxygen binding was present in all hemoglobins with Hill's coefficient, n, ranging from 1.21 +/- 0.14 in Dissostichus mawsoni to 2.28 +/- 0.88 in T. borchgrevinki among the Nototheniidae, and n = 1.50 +/- 0.14 in G. acuticeps. 4. A small increase in P50- was promoted by ATP for hemoglobins from T. borchgrevinki, T. bernacchii and D. mawsoni but significant temperature effects on oxygen binding were manifested, with apparent heats of oxygenation, delta H, = -56.13, 62.16, and -23.98 kJ mol-1, respectively.