Ontogeny of the gastrointestinal tract of marine fish larvae

Abstract

Marine fish larvae undergo major morphological and cellular changes during the first month of life. The ontogeny of the gastrointestinal tract combines these two aspects of the larval development and is very interesting in that the timing of functional changes appears genetically hard-wired. The goal of this paper is to give an overview of the gastrointestinal development process in marine fish larvae, with particular attention to three species: sea bass; red drum; and sole, since the description of gut maturation in fish larvae was initiated during the last decade with these species. During the early stages, marine fish larvae exhibit particular digestive features. Concerning the exocrine pancreas, amylase expression decreases with age from the third week post-hatching in sea bass and red drum (approximately 400 degree days), whereas expression of other enzymes (trypsin, lipase, phospholipase A2…) increases until the end of the larva period. Moreover, secretory function of the exocrine pancreas progressively develops and becomes efficient after the third week of life. Concerning the intestine, enzymes of the enterocyte cytosol (in particular peptidase) have higher activity in young larvae than in older. Approximately in the fourth week of post-hatching development in sea bass, red drum and sole larvae, the cytosolic activities dramatically decline concurrently with a sharp increase in membranous enzyme activities of the brush border, such as alkaline phosphatase, aminopeptidase N, maltase... This process characterises the normal maturation of enterocytes in developing fish larvae and also in other vertebrates' species. The establishment of an efficient brush border membrane digestion represents the adult mode of digestion of enterocytes. This paper also describes the role of diet on the development of the gastrointestinal tract. Indeed, the maturational process of digestive enzyme can be enhanced, stopped, or delayed depending on the composition of the diet.Please note th Fig. 5. Activities and mRNA levels of phospholipase A2 (PLA2) during the development of sea bass larvae fed different dietary phospholipid levels (from ref. 57). J J J J J PL 2,4% PL 3,4% PL 45% PL 5,7% PL 6,6% 0

Gene Expression Patterns During the Larval Development of European Sea Bass (Dicentrarchus Labrax) by Microarray Analysis

“…Based on these expression patterns, samples were grouped into two large clusters, the first group encompassing most larval samples taken from 7 to 23 dph, the second containing those sampled from 25 to 43 dph. The period ranging from 17 to 31 dph, during which the larval transcriptome underwent large changes, could correspond to the maturation of physiological functions and associated changes in the energetic metabolism already described in some previous studies (Zambonino-Infante & Cahu, 2001;Parra & Yufera, 2001). Usually, this type of overall classification cannot detect differential gene expression between samples properly, due to the excessive noise generated by unregulated genes.…”

“…The appearance of a fully developed stomach and acid digestion is considered as the end of the transition from the larval to the juvenile stage and the beginning of adult-type feeding characteristics in fish (Govoni et al, 1986). The expression of gastricsin precursor revealed that sea bass larvae began to acquire the adult mode of digestion at 25 dph, in accordance with the appearance of gastric glands (Zambonino-Infante and Cahu, 2001). The decrease in expression level of trypsin precursors, combined with the most intense gastricsin expression level at 43 dph, illustrates the importance of acid digestion in sea bass.…”

“…Such expression patterns agree with a progressive adaptation of digestive enzymes of reared larvae to diets containing around 60% protein. It is well known that the most important step in digestive system development of a carnivorous fish is the transition from less efficient basic protein digestion in the intestinal lumen, to more efficient acidic protein digestion that becomes effective once the gastric glands of the stomach are completely functional (Zambonino-Infante and Cahu, 2001;Darias et al, 2005Darias et al, , 2007b. The appearance of a fully developed stomach and acid digestion is considered as the end of the transition from the larval to the juvenile stage and the beginning of adult-type feeding characteristics in fish (Govoni et al, 1986).…”

“…Largely, post embryonic development will transform an organism that initially has only a rudimentary or non functional liver, pancreas, gallbladder and spleen, undifferentiated skeleton, incompletely developed nervous system and no gills, into a juvenile with a mature digestive tract and developed nervous system, calcified skeleton, final fins, finrays, a thick skin and functional gills (FalkPetersen, 2005). Studies performed on marine fish have particularly demonstrated the importance of enzymatic regulation in the digestive tract (Zambonino-Infante and Cahu, 2001) and variation in energetic metabolism (Wieser, 1995) during larval development. However, more exhaustive molecular approaches are needed to identify the genes involved in regulation of the key biological changes occurring during marine fish larval development.…”

Screening of enzyme activity for assessing the condition of larvae in the seven-band grouper Epinephelus septemfasciatus and devil stinger Inimicus japonicus

“…A pancreatic enzyme as trypsin is synthesized in the pancreas while intestinal enzymes as esterase and alkaline phosphatase are synthesized in intestine. Activity of all measured enzymes in this study is mainly involved in the intensity of digestion and nutrient absorption of larvae, therefore, the increase in those activities with ages of seven-band grouper and of devil stinger may relate to the development of pancreas and an increase in the area of the intestine [11,[26][27]. This is supported by the increases in NL, TL and growth rate with ages of both larval species.…”