GASTRIC EVACUATION IN THREE SIZES OF GROW-OUT ATLANTIC HALIBUT Hippoglossus hippoglossus FED DIFFERENT PELLETS SIZES

Introduction

 The  production of farmed  Atlantic  halibut  has  stagnated with an average production of  1686  tons/year since 2007

 .  One of the major bottlenecks hindering  the  expansion of the industry is the slow growth rates of halibut above 1kg (grow-out phase), linked  to  the low feed intake rates observed. Ingestion of feed requires appetite stimulating signals such as visual, olfactory, and physiological sensation of hunger. The amount  of feed ingested  is  eventually  limited  by  the  filling  capacity of the stomach and  generally  appetite decreases during feeding as satiation (fullness of the stomach) increases

. After ingestion of a meal , the food in the stomach is mechanically and chemically digested before  it is gradually evacuated from the stomach and  enter the intestine for further digestion,  followed by  absorption, and assimilation of nutrients. The effectiveness of digestive processes is affected by several parameters, including fish size

 , water temperature

, meal size and type of food. Halibut appetite varies on a day-to-day basis , and it has been observed that it prefers to eat a small meal the day after a large meal

. This suggests that halibut may have a  relatively slow  gastric evacuation time, negatively affecting the time to next meal . In this study we investigated the gastric evacuation time  for 3 different Atlantic halibut sizes using different pellet sizes .

Material and methods

Three size groups (1, 2 and 3 kg) of  Atlantic  halibut  in duplicates  were randomly allocated to 12 tanks with a bottom surface of 4. 9 m2 supplied with fresh seawater with a mean temperature of 8.9 °C and 91 % O2 .  After  the acclimatization period of 14 days, where the fish were hand fed every day using a commercial diet (Hippo Express, Skretting, Norway), the halibut were deprived of food for 120 hours to ensure no feed  residuals  were present in the gastrointestinal tract (

 . The fish  groups  were then fed a single meal ad libitum  with respective pellets sizes (7, 9, 13 and 17 mm), and 3 fish were sampled from each tank at 1, 3, 6, 10, 23, 32, 48, 71, 96 and 120 hours after feeding. The content of stomach, pyloric caeca, midgut and hindgut were collected as well as  information regarding the round weight, fork length, sex and weight of gonads, liver and heart. Content of  the gastrointestinal  tract compartments were dried for 48 h at 105 °C and the dry weight normalised to the  fish weight.

Results and discussion

 The maximal meal ingested by any fish was  1.1  % of body weight . However, there was a large variability, and some fish did not ingest any feed despite 120 hours of fasting.  Preliminary  analysis of the data indicates a negative relationship between pellet size and feed intake (measured at 1h).  To determine the optimal feeding frequency for Atlantic halibut, gastric evacuation time should be accounted for , since satiation is mainly affected by the fullness of the stomach

. In our study, the dry weight of the s tomach content  was  reduced to 50 %  at 14 hours after feeding and  25 % after 23 hours (Figure 1) .  This result might explain the variable day-to-day feed ingestion levels observed in commercial halibut farms and the results obtained by

. The content of the p yloric caeca  and  midgut  reached  the highest dry weight at 23 hours,  and hindgut at 71 hours . No feed residuals were  observed in the gut at 120 hours  which corresponds with previous observations

.  This study provides valuable information to design optimal timed feeding regimes for grow-out Atlantic halibut.

Sources

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