Abstract
Studies on digestive adjustments at the biochemical level in relation to salinity in euryhaline crabs are lacking. Moreover, knowledge of biochemical digestive characteristics of euryhaline crabs (i.e. occurrence and characteristics of key digestive enzyme activities) is still scarce and fragmentary. We studied the occurrence, characteristics and response to low salinity of amylase, maltase and sucrase activities in the hepatopancreas of the euryhaline crab Neohelice (Chasmagnathus) granulata . Maximal amylase and maltase activities were found at pH 5.2. Sucrase activity was maximal within the pH range 3.6-5.2. Amylase, maltase and sucrase activities showed a Michaelis-Menten kinetics (km = 0.41±0.10 mg ml -1 ; 1.37±1.03 mM and 0.55±0.45 mM, respectively). In crabs acclimated to low salinity (10 psu; hyperregulating conditions), amylase activity (7263±980 μg maltose min -1 mg prot -1 ) was higher than in 35 psu (osmoconforming conditions) (3605±340 μg maltose min -1 mg prot -1 ). Maltase and sucrase activities (497±98 and 64±16 μg glucose min -1 mg prot -1 , respectively) were similar in both salinities. The response of amylase activity to low salinity suggests a role in digestive adjustments upon hyperregulation. This study contributes to a better understanding of the complexity of the biochemical adaptations to low salinity in euryhaline crabs.
Highlights
Euryhaline crabs inhabiting coastal waters, tide areas or estuaries are exposed to frequent and abrupt changes in the environmental salinity that require biochemical, physiological, morphological and/or behavioural strategies for controlling movements of water and ions between the individuals and their medium (Anger, 2001)
Characteristics and response to low salinity of amylase, maltase and sucrase activities in the hepatopancreas of the euryhaline crab Neohelice (Chasmagnathus) granulata
In crabs acclimated to low salinity (10 psu; hyperregulating conditions), amylase activity (7263±980 μg maltose min-1 mg prot-1) was higher than in 35 psu (3605±340 μg maltose min-1 mg prot-1)
Summary
Euryhaline crabs inhabiting coastal waters, tide areas or estuaries are exposed to frequent and abrupt changes in the environmental salinity that require biochemical, physiological, morphological and/or behavioural strategies for controlling movements of water and ions between the individuals and their medium (Anger, 2001). In spite of the extensive work that has been done on different aspects of the adaptive responses of hyperregulating crabs to low salinity, studies on the possible digestive adjustments at the biochemical level (i.e. modulation of the activity of key digestive enzymes) are lacking. The effect of extreme environmental salinity on digestive enzymes activities (i.e. total amylase activity) has been shown to occur in the hepatopancreas of the euryhaline pacific white shrimp Litopenaeus vannamei, suggesting the possibility of deriving extra energy upon osmoregulation (Li et al, 2008)
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