Effects of different vegetable oils on growth performance, fatty acids and thermal tolerance of the Turkish crayfish Astacus leptodactylus

This study is comprised of two experiments. In the 1st Experiment, Turkish crayfish Astacus leptodactylus (24 g) were fed with different vegetable oil sources [peanut oil (PO), cotton seed oil (CSO), linseed oil (LO) and hazelnut oil (HO)] as substitute for fish oil (FO: control) in the diet. In the 2nd Experiment, the effects of vegetable oil-based diets on thermal tolerance of the crayfish were examined, while furthermore, at three acclimation temperatures, CTMin and CTMax values, acclimation response ratio (ARR) and thermal tolerance polygon (15, 20 and 25C) were also studied. In the 1st Experiment, among five different diets that were fed to the juveniles for 60 days, HO sustained the highest final weight (P<0.05). While FCR was calculated as 1.53 in this group, this value ranged between 2.15 and 2.50 in other experimental groups. In general, in spite of their very low level of EPA (20:5n-3) and DHA (22:6n-3), vegetable oil sources promoted good growth, high nutritional contents and successful moultings throughout the study. The reason for this is attributed to high contents of MUFA's in the vegetable oils that can be more efficiently converted through β-oxidation to energy, as compared to n-6 PUFA's. Accumulation of MUFA's was highest in LO (35.51%) and HO (35.02%) in the abdominal tissue, especially 18:1n-9 in HO (25.06%) (P<0.05). This fatty acid was measured as 22.30, 19.76, 19.57 and 19.20% in PO, LO, FO and CSO, respectively. As expected, highest EPA was found in FO, but this fatty acid was also accumulated in the groups feeding on vegetable oil sources to a level close to the control group. DHA level was found to also be highest (9.76%) in the group feeding on FO (P<0.05), while this fatty acid ranged between 7.70 and 6.84% in the groups feeding on vegetable oil sources. The richest group in terms of PUFA's was found as FO (46.36%, P<0.05) followed by PO and CSO (44.56% and 43.34%), while poorest were LO and HO-groups (40.08 and 42.40%). Protein digestibility ranged from 97.1 to 98.4%, while dry matter ranged from 61.8 and 72.9% . Our results have shown that, PO and HO feeds, which contained high levels of MUFA's, can fully substitute FO in the feed of A. leptodactylus, on condition that fish and squid meals are used at 26% in the formulation. In the 2nd Experiment, thermal tolerance tests were shown that acclimation temperatures (15, 20 and 25C) had significant effects on CTMin ve CTMax values of A. leptodactylus juveniles (P<0.05). At a heating/cooling rate of 0.3C/min the CTMin values ranged between 1.3 and 2.0C, while the CTMax values ranged between 37.4 and 38.7C. Thermal tolerance polygon area was calculated as 364°C2. At three acclimation temperatures (15, 20 and 25°C), the ARR values ranged from 0.13 to 0.23. The CTMin and CTMax values dropped down to 0.5C or went up to 40.1C when the juveniles were fed vegetable oil-based diets (P<0.05). Our study has demonstrated that, when the crayfish were fed on LO or HO for 60 days, their tolerance to extreme temperatures could significantly be enhanced, while increaser of tolerance to low temperatures was more evident in this respect.