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presented high values, whereas other carnivores such as the European eel ( A. anguilla )
and the gilthead sea bream ( Sparus aurata ) exhibited lower activities. However, when the
phylogenetic parameter is taken into account and comparison is made between species
of the same group, the hypothesis as to whether herbivores have higher amylase activi-
ties (α-amylase) than those of carnivores, and carnivores have higher protease activities
(pepsin, trypsin) than those of herbivores, is less evident. Whereas Fernandez et al. (2001)
found that differences of α-amylase activities in five species of Mediterranean sparids
(family Sparidae) are primarily related to their feeding habits, other researchers (Chan
et al. 2004; German et al. 2004) observed from studying four fish species of the family
Stichaeidae, the shannies, that it was the phylogenetic link that predominantly affected
the α-amylase activities. Chakrabarti et al. (1995), studying the activity of several digestive
enzymes (α-amylase, cellulase, invertase, esterase, acid, and alkaline proteases) in 11 spe-
cies of bony fish from one lake, also observed that there was no correlation between these
enzyme activities and the feeding habits of the fish. Researchers attributed these results
to fish habitats: life in a lake involves significant alimentary niche overlap of the different
species within this system (Chakrabarti et al. 1995).
11.5.1.2 Aquatic Invertebrates
A relationship between the alimentary regime and the production of digestive enzymes
is often found in invertebrates. Raised levels of enzyme activity according to the sub-
strate most frequently present in the diet have been observed in a decapod crustacean,
the shrimp Litopenaeus vannamei (Moss et al. 2001). Amylase and protease activities are
thus modulated by the food composition in different species of shrimps and increase with
the respective content of alimentary carbohydrates and proteins (Ceccaldi 1998). Mayer
et al. (1997) studied relationships between different digestive enzymes in species of poly-
chaetes, echinoderms, and holothurians. Lipase activities are generally higher in carnivo-
rous polychaetes compared to other detritivorous species. The lipase/protease (L/P) ratio
proves to be a food source indicator. In carnivorous polychaetes the L/P ratio is greater
than 1, whereas in detritivorous species it is lower than 0.04.
In different species of crab, Johnston and Freeman (2005) also observed variations in
digestive enzyme activities according to alimentary regime. Nectocarcinus integrifons eats
marine higher plants and shows elevated cellulase activity in order to degrade cellu-
lose. Petrolisthes elongates, which consumes phytoplankton and brown and green algae,
shows raised laminarinase and β-glucosidase activities for digesting laminarin. Finally,
Leptograpsus variegates , which has an omnivorous alimentary regime, presents increased
activities of protease, α-glucosidase, and α-amylase, making best use of alimentary pro-
teins and carbohydrates. Other research has also shown, according to species, elevated
levels of enzyme activities in carnivores, moderate levels in omnivores, and low levels
in herbivores (Jones et al. 1997; Kumlu and Jones 1997; Le Vay et al. 2001; Gutow et al.
2006). However, certain species do not show a relative importance of a particular class
of enzyme. These species may have a very varied alimentary regime, as observed in the
crab Carcinus maenas (Johnston and Freeman 2005), in turn, related to the large number of
habitats occupied by this species.
Although the measurement of digestive enzymes is a commonly used tool for clas-
sification of alimentary regimes in many invertebrates, with the hypothesis that diges-
tive enzymes activities are higher for the most common substrates in the diet (Gaudy
and Boucher 1983; McClintock et al. 1991; Brêthes et al. 1994; Johnston and Freeman 2005;
Johnston et al. 2005), the data are sometimes contradictory. Thus, Rodriguez et al. (1994)
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