Water temperature effects on growth performance, proximate body and tissue composition, morphometric characteristics and gastrointestinal evacuation processes of juvenile meagre, Argyrosomus regius (Asso 1801)

The effect of 4 temperature levels, 17, 20, 23 and 26 degrees C was investigated on growth performance, feed and nutrient utilization, body, fillet and liver composition and morphometric characteristics of meagre, of initial mean weight 36.46 g, after a 12-week trial, fed on a practical diet composed of 49% crude protein and 16% lipids (dry weight). Furthermore, the gastrointestinal evacuation processes of meagre were monitored by subjecting fish to 48-h fasting period, followed by force-feeding and collecting the stomach and intestinal contents at 1 h, 2 h, 4 h, 6 h, 8 h, 12 h and 24 h post-feeding. Meagre growth parameters significantly improved with the increase in temperature, resulting in double the thermal growth coefficient (TGC) at 23 and 26 degrees C compared to 17 degrees C. Maximum weight (122.5 g) was achieved at 26 degrees C. Daily feed intake (DFI) increased from 17 to 26 degrees C, whereas nutrient efficiency and utilization parameters were significantly lower only at 17 degrees C. A time effect was also evident on the growth-related parameters and feed conversion ratio (FCR), resulting in similar specific growth rate (SGR) and TGC values between 23 and 26 degrees C and lower FCR only in 17 degrees C by the 3rd month, despite the initial difference amongst the 4 treatments. Intestine length increased as fish grew bigger with temperature increase, but the relative intestine length to fish total length remained constant. No effect of temperature was found on condition index (CI), hepatosomatic index (HSI), body proximate composition, fillet lipids and liver glycogen content. Liver lipid content significantly increased from 17 degrees C to 26 degrees C. Temperature influenced gastric evacuation patterns, but not the digesta moisture in each gastrointestinal tract (GIT) segment. Hydration within the GIT was affected by temperature with lower content obtained at 17 degrees C. Stomach digesta moisture and hydration significantly elevated 4 h post-feeding in all treatments. Within the intestine, unlike in the stomach, digesta were mostly comprised of moisture. Gastric evacuation rate (GER) became faster with temperature increase. Meagre juveniles required 4.3-7.4 h to half-empty their stomachs depending on temperature and more than 24 h to completely evacuate their GIT. 23-27 degrees C was determined as the best water temperature range for growth of meagre of 36-123 g under the specific culture conditions. At 17 degrees C growth and feed efficiency were impaired, while gastric evacuation processes deviated from the rest.