The incidence of different pellet size on growth, gut evacuation, feed digestibility and feed waste in gilthead sea bream (Sparus aurata)

The feeding behaviour of gilthead sea bream (Sparus aurata) consists in cracking and chewing feed. In farming condition, this results in crushing feed pellets with an occasional loss of some fragments which can vary in response to pellet dimension, thus affecting feed waste at the on-growing stage. However, few studies have addressed this issue and even less information on the further effect of different pellet size on growth, gut evacuation and feed efficiency are available on this species. Thus, a 122-day study was undertaken to assess the effects of three pellet size (2 mm, S; 4 mm, M and 6 mm, L) on growth, gut evacuation, feed waste and feed digestibility during the on-growing of gilthead sea bream (initial weight: 215.9 +/- 1.8 g). No significant effects of pellet size on growth (final body weight and SGR) were observed. Pellets diameters had no effects on feed digestibility (protein and dry matter) and feed efficiency parameters (FCR, PER, GPE, GLE) even if differences in the gastric evacuation rate were detected at different pellet size. At this regard, the shape-rate model developed to estimate the gastrointestinal evacuation pattern, evidenced a slower gastric evacuation rate in the 6 mm diet, while no differences in foregut evacuation rate were observed. Data on feed waste, highlighted how feed losses by chewing was practically absent in the S (2 mm) diet while in the M (4 mm) and L (6 mm) diets 24.3 and 17.3% of the entire meal was losses by chewing activity, respectively. The study reinforces previous observation that feeding pellets size of 4 and 6 mm in gilthead sea bream within 200-450 g could induced an excess of feed waste by chewing activity with economic and environmental implication. Despite the reduced feed intake observed, pellets size of 2 mm did not lead to any feed losses by chewing and was able to guarantee similar growth compared to the other diets. Further studies considering intermediate pellets size (3 mm) may be useful in order to further optimize the pellet size choice during the on-growing phase of this species

Effect of temperature and diet on wound healing in Atlantic salmon (Salmo salar L.).

Compromised skin integrity of farmed Atlantic salmon, commonly occurring under low temperature and stressful conditions, has major impacts on animal welfare and economic productivity. Even fish with minimal scale loss and minor wounds can suffer from secondary infections, causing downgrading and mortalities. Wound healing is a complex process, where water temperature and nutrition play key roles. In this study, Atlantic salmon (260 g) were held at different water temperatures (4 or 12 °C) and fed three different diets for 10 weeks, before artificial wounds were inflicted and the wound healing process monitored for 2 weeks. The fish were fed either a control diet, a diet supplemented with zinc (Zn) or a diet containing a combination of functional ingredients in addition to Zn. The effect of diet was assessed through subjective and quantitative skin histology and the transcription of skin-associated chemokines. Histology confirmed that wound healing was faster at 12 °C. The epidermis was more organised, and image analyses of digitised skin slides showed that fish fed diets with added Zn had a significantly larger area of the epidermis covered by mucous cells in the deeper layers after 2 weeks, representing more advanced healing progression. Constitutive levels of the newly described chemokines, herein named CK 11A, B and C, confirmed their preferential expression in skin compared to other tissues. Contrasting modulation profiles at 4 and 12 °C were seen for all three chemokines during the wound healing time course, while the Zn-supplemented diets significantly increased the expression of CK 11A and B during the first 24 h of the healing phase