Allometric growth and functional development of the gut in developing cod Gadus morhua L. larvae
Abstract:The development of the gut epithelium in cod Gadus morhua was studied during the larval period in intensive rearing systems. Cod larvae were fed enriched rotifers from mouth opening. On 17 days post-hatch (dph) one group of larvae were fed Artemia sp. nauplii while another group were fed both rotifers and a formulated diet (co-fed). At the end of the experiment (30 dph) larvae receiving live feed were almost three times larger than the co-fed larvae, although no clear signs of pathological effects due to feeding regime were found in any larvae sampled for morphological studies. The midgut volume in larvae fed live feed increased by a factor of 38 during the experiment, and in particular volume increased rapidly between 24 and 30 dph. The enterocyte size increased between 12 and 24 dph from 652 ± 64 to 1479 ± 144 m3 (mean ±s.e.). When enterocytes reached their maximum size, several morphological changes in the gut epithelium were initiated, such as increased number of mitochondria per enterocyte, increased size of the nuclei and a considerable increase in microvilli surface area. The mitochondrial membrane structures changed during the experiment, suggesting a maturation process of the mitochondria. The midgut development was strongly related to larval size rather than age. On 30 dph co-fed larvae were equal in size to Artemia sp. fed larvae on 24 dph. This was reflected by equal values of estimated midgut volume, midgut length and total number of enterocytes and the number of mitochondria per enterocyte. The microvilli surface area, however, was significantly larger in co-fed larvae on 24 dph compared to live-feed larvae on 30 dph. This increase in absorptive surface was probably a response to suboptimal feeding conditions. The strong correlation between gut development and larval size and the lack of clear pathological effects, suggested that the gut tissue is flexible and can withstand periods of suboptimal nutrition at this stage.
Document Type: Regular Paper
Publication date: May 1, 2008