W.M. Koven, R.J. Henderson, J.R. Sargent-1997

Aquaculture, 151: 155-171

Abstract:

In-vivo and in-vitro studies were carried out to evaluate lipolytic

activity in the gut of juvenile turbot. The in-vivo study examined total

lipid (% DW digesta), neutral and phospholipid classes (% total lipid,

mg/g DW digesta) and the fatty acid compostion of the neutral lipid

classes (% wt. of lipid class), as a function of hydrolysis, in the

digesta of the stomach, foregut, hindgut and rectum of 50-60 g

juvenile turbot. In contrast with earlier investigations, this study

found the highest lipolytic activity and absorption occurring in the

hindgut and rectum. In addition, various fatty acid groups showed

differential uptake in this region which can be expressed, in order of

increasing absorption, as saturates < monoenes < polyunsaturates.

The in-vitro study investigated the lipolytic ability of digesta from

different segments of the turbot digestive tract to hydrolyse the

14C-labelled lipid substrates: triacylglycerol (TAG), cholesterol ester

(CE) and phosphatidylcholine (PC). Consistent with findings in the

in-vivo analysis, the pattern of hydrolysis was repeated in all

substrates tested and can be expressed in order of increasing

hydrolytic activity as stomach < foregut < hindgut < rectum.

Moreover, both studies suggested a non-specific lipolysis and

phospholipid hydrolysis occurring in the posterior region of the gut

particularly the rectum.

The combined results of these studies concluded that the major site

for lipolysis and absorption in juvenile turbot resides in the

hindgut-rectum region. Future research should focus on the potential

contribution of highly lipolytic bacteria in the posterior gut, such as

Vibrio spp., which have been shown to effectively hydrolyse fish oils.

(National Center for Mariculture, Israel Oceanographic and

Limnological Research Ltd, P.O.B. 1212, Eilat, 88112, Israel)

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