Digestion of protein and amino acid absorption in stomachless fish, common carp (Cyprinus carpio L.)

Daily rhythms of intestinal cholecystokinin and pancreatic proteases activity in Senegalese sole juveniles with diurnal and nocturnal feeding

The influence of diurnal and nocturnal feeding on daily rhythms of gut levels of cholecystokinin (CCK) and the activity of two key pancreatic proteases, trypsin and chymotrypsin, were examined in juveniles of Senegalese sole (Solea senegalensis), a species with nocturnal habits. Four feeding protocols were performed: P1) One morning meal; P2) Six meals during the light period; P3) Six meals during the dark period; and P4) 12 meals during 24 h. Daily activity patterns of both proteases were remarkably similar and showed a high correlation in all the experimental protocols. In P1, daily patterns of CCK and digestive enzymes showed a single maximum. In P2, CCK levels exhibited two peaks. Digestive enzymes activities showed slightly delayed peaks compared to CCK, although their daily fluctuations were not significant. In P3, intestinal CCK concentration exhibited two peaks at the end of light and dark periods, but only the second one was significant. The first maximum level of chymotrypsin activity occurred 4 h after the first CCK peak, while the second one coincided with the second CCK peak. Fluctuations of trypsin activity were not significant. In P4, CCK concentration showed three small peaks. Digestive enzymes daily fluctuations were not significant, although they showed an inverted trend with respect to CCK. The daily pattern of the gut CCK content in our study is in agreement with the anorexigenic function of this hormone. Our results support the existence of a negative feedback regulatory loop between CCK and pancreatic proteolytic enzymes in Senegalese sole juveniles.

Consistent individual differences in seed disperser quality in a seed-eating fish

Animal-mediated seed dispersal (zoochory) is considered to be an important mechanism regulating biological processes at larger spatial scales. To date, intra-specific variation in seed disperser quality within seed-dispersing animals has not been studied. Here, I employed seed feeding trials to quantify individual differences in disperser quality within the common carp (Cyprinus carpio) using seeds of two aquatic plants: unbranched bur-reed (Sparganium emersum, Sparganiaceae) and arrowhead (Sagittaria sagittifolia, Alismataceae). I found substantial variation among carp individuals in their propensity to ingest seeds and their ability to digest them, resulting in up to 31-fold differences in the probability of seed dispersal. In addition, there were significant differences in the time that seeds are retained in their digestive systems, generating a twofold difference in the maximum distance over which they can potentially disperse seeds. I propose that seed-eating animal species consist of individuals that display continuous variation in disperser quality, with at one end of the continuum individuals that are likely to eat seeds, pass them unharmed through their digestive tract and transport them over large distances to new locations (i.e. high-quality seed dispersers) and at the other end individuals that rarely eat seeds, destroy most of the ones they ingest and transport the few surviving seeds over relatively short distances (low-quality seed dispersers). Although individual differences in seed dispersal quality could be the result of a variety of factors, these results underline the ecological and evolutionary potential of such variation for both plants and animals.

Plasma essential amino acids changes in sea-bass (Dicentrarchus labrax) after feeding diets deficient and supplemented in L-methionine

A fishmeal-based reference diet, a soybean-yeast-based methionine (MET)-deficient diet and two MET-supplemented diets were fed to groups of yearling sea-bass, reared in sea-water at 21 +/- 1 degrees C. Levels of most free essential amino acids (EAA) reached a maximum concentration in plasma between 4 and 8 hr after a single meal. Plasma MET level remained very low with the deficient diet, exhibiting by 4 hr a 10-fold reduction when compared to the reference diet, although MET content was divided only by two in the former. Daily MET intake was then maintained under minimum requirement in fish fed the deficient diet. Supplemented MET reached peak level in plasma substantially sooner than the rest of the EAA, indicating faster absorption and degradation when compared to MET incorporated in feed proteins. Evolution of methionine sulfoxide (MSO) levels in plasma after feeding MET-supplemented diets gives evidences that a degradation pathway of MET into MSO exists in sea-bass.

Comparative aspects of protein digestion and amino acid absorption in fish and other animals

1. Molar concentrations of amino acids in the content of subsequent parts of alimentary tract of rainbow trout and common carp have been calculated. 2. The ratio of free amino acid concentration in intestinal content to blood of carp most commonly was between 10 and 20 and decreased as digestion proceeded. 3. Free amino acid concentration in gut content of fish appeared several times higher than that in reptiles or mammals. 4. Absorption rate of amino acids in carp was most intense during the first 3 hr after feeding and generally similar to that found in caymans. 5. Release rate of amino acids from dietary protein was most intense in the second segment of carp intestine where most of amino acids were also absorbed. 6. Requirements of essential amino acids based on their absorption rate were determined.