Feeding protocol modulates the daily gastrointestinal transit in gilthead seabream juveniles

Abstract

Improving the growth performance in farmed fish is a permanent challenge. There is a vast knowledge in feed formulation and digestibility of different ingredients. However, few studies have addressed the gastrointestinal tract (GIT) parameters per se as fundamental factors that should be considered in the digestive process. Therefore, this work aimed to evaluate the changes of the ingesta transit rate throughout the GIT in response to different feeding protocols in gilthead seabream (Sparus aurata). Juvenile fish (17.66 ± 0.38 g) were distributed into 4 groups (250-L tanks, 19.5 ± 1.0 °C, photoperiod 11L/13D). All groups were fed a daily ration of 2 % body mass during the daylight with different feeding protocols: (a) 1 meal (08:30 h); (b) 3 meals (08:30, 13:30, and 18:30 h); (c) 5 meals (08:30, 10:30, 13:30, 16:30 and 18:30 h); and (d) continuous feeding. Fish were acclimatized before sampling during two weeks. To determine the GIT transit (filling and evacuation time), fish were alternatively fed with diets with and without Yttrium, as an inert marker. Yttrium was measured separately in the stomach and intestine by ICP-MS. Stomach and intestine became full 4 to 12 h after feeding, depending on the protocol (Fig. 1A, B) and were emptied between 8 to 12 h and 12-16 h, respectively (Fig. 1C, D). Fish fed one single meal showed the fastest filling rate, both for the stomach and the intestine, although their evacuation time were comparable to the rest of the groups. Fish fed five daily meals showed the fastest stomach evacuation rate; however, their intestine evacuation was similar to the rest of the groups. Juveniles with the continuous daily feeding had the longest intestine evacuation time (around 16 h). Our results indicated that feeding the gilthead seabream with a single meal, allocating the whole daily ration, leaded to a very fast stomach transit. However, splitting the daily ration in several meals resulted in longer transit times, especially during the intestinal digestion period. These findings highlight the importance of the feeding protocol on the GIT transit time, and in the duration that the ingesta is exposed to different luminal chemical environments and digestive enzymes, and, therefore, in the efficiency of the feeding practice.