Digestive Enzyme Profiles Research Articles

Toxicity effects of hexavalent chromium on hematological, biochemical and digestive enzyme profiles of Labeo rohita (Hamilton, 1822).

The study provides a descriptive understanding of the toxic effect of heavy metal chromium on the hematological, biochemical, and digestive enzyme profiles in the fingerlings of Labeo rohita. The 96-h LC50 of hexavalent chromium was found to be 15.76 mg/L. Further, the toxicity study was conducted with four different sub-lethal concentrations of 96-h LC50 viz. 1/40th, 1/20th, 1/10th, and 1/5th respectively. The blood samples from the control and treated groups exposed to different concentrations were examined for various physiological parameters. The obtained data showed that, with the increase in sub-lethal concentration, a significant decrease (p < 0.05) in red blood cell (RBCs), hemoglobin (Hb), and hematocrit (Hct) was observed, while total white blood cell (WBCs), mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) increased significantly (p < 0.05) in all the treatments. Fishes exposed to chromium for 30 days responded by becoming hyperglycemic, hyperproteineric, and hypoalbuminemia with a gradual rise in concentrations. Alteration in the intestinal digestive enzyme profiles was also observed after 30 days of study. The activity of protease (89.76%), and amylase (41.88%) decreased in the intestine with the highest concentration compared to the control. Conversely, compared to the control, the highest concentration resulted in an increase (146%) in lipase activity. Overall, this study has greatly enhanced our comprehension of the impact of chromium toxicity on various hematological, biochemical, and digestive enzyme parameters in Labeo rohita.

Sea cucumbers and their symbiotic microbiome have evolved to feed on seabed sediments

Sea cucumbers are predominant deposit feeders in benthic ecosystems, providing protective benefits to coral reefs by reducing disease prevalence. However, how they receive sufficient nutrition from seabed sediments remains poorly understood. Here, we investigate Holothuria leucospilota, an ecologically significant tropical sea cucumber, to elucidate digestive mechanisms underlying marine deposit-feeding. Genomic analysis reveals intriguing evolutionary adaptation characterized by an expansion of digestive carbohydrase genes and a contraction of digestive protease genes, suggesting specialization in digesting microalgae. Developmentally, two pivotal dietary shifts, namely, from endogenous nutrition to planktonic feeding, and from planktonic feeding to deposit feeding, induce changes in digestive tract enzyme profiles, with adults mainly expressing carbohydrases and lipases. A nuanced symbiotic relationship exists between gut microbiota and the host, namely, specific resident bacteria supply crucial enzymes for food digestion, while other bacteria are digested and provide assimilable nutrients. Our study further identifies Holothuroidea lineage-specific lysozymes that are restrictedly expressed in the intestines to support bacterial digestion. Overall, this work advances our knowledge of the evolutionary innovations in the sea cucumber digestive system which enable them to efficiently utilize nutrients from seabed sediments and promote food recycling within marine ecosystems.

Effect of ivermectin, amitraz and fipronil on midgut epithelium and digestive enzyme profile in Rhipicephalus microplus ticks (Acari: Ixodidae).

Blood feeding and digestion are vital physiological activities essential for the survival and reproduction of ticks. Chemical acaricides viz., ivermectin, amitraz and fipronil, are known to act on the central nervous system, resulting in the mortality of ticks. The present study is focused on the effect of these acaricides on the midgut and gut enzymes ofRhipicephalus microplus.The ultra-thin sections of midgut of ivermectin-treated ticks showed irregular basal membrane and ruptured digestive vesicles. Amitraz treatment resulted in a notable decrease in digestive cells with pleats in the basal membrane, while fipronil-exposed ticks exhibited reduced digestive cells, loss of cellular integrity, and disintegration of the basal membrane and muscle layer.The gut tissue homogenate of ivermectin and fipronil treated ticks showed a significant reduction of cathepsin D level, 76.54 ± 3.20 μg/mL and 92.67 ± 3.72 μg/mL, respectively, as compared to the control group (150.0 ± 3.80 μg/mL). The leucine aminopeptidase level (4.27 ± 0.08 units/mL) was significantly decreased in the ivermectin treated ticks compared to other treatment groups.The acid phosphatase activity (29.16 ± 0.67 μmole/min/L) was reduced in the ivermectin treated group whereas, increased activity was observed in the fipronil and amitraz treated groups. All the treatment groups revealed increased alkaline phosphatase levels (17.47-26.72 μmole/min/L). The present finding suggests that in addition to the established mechanism of action of the tested acaricides on the nervous system, the alterations in the cellular profile of digestive cells and enzymes possibly affect the blood digestion process and thus the synthesis of vital proteins which are essential for vitellogenesis, and egg production in ticks.

Performance of crustacean and insect meal based diets on the growth and digestive enzyme profile of pearlspot Etroplus suratensis (Bloch, 1790)

A feeding trial of 75 days was conducted in tanks to study the performance of shrimphead meal (SM), crab shell meal (CM) and silkworm pupae meal (SWP) on the growth anddigestive enzyme profile of pearlspot, Etroplus suratensis. Four iso-nitrogenous diets with31.5% crude protein replacing 50% fishmeal (FM) in the diets were formulated viz., SM (T1),CM (T2), SWP (T3) and a control (C). Pearlspot advanced fry, 2 cm in length and 1.1 g inweight, was stocked at 60 nos per tank. After 75 days of the experiment, feed conversionratio (FCR), feed efficiency ratio (FER) and protein efficiency ratio (PER) were observed to besignificantly better (p&lt;0.05) in all treatment groups (T1, T2 and T3) than in control (C). T2 (CM)fed fishes exhibited a maximum specific growth rate (SGR) of 3.25±0.09, and significantlyhigher (p&lt;0.05) weight gain (11.54±0.78 g) than T1, T3 and control. In enzyme assays, T2 (CM) fedfishes exhibited significantly higher (p&lt;0.05) protease activity than other treatments.Lipase activity was significantly higher (p&lt;0.05) in T3. However, there was no significantdifference with control diet-fed fishes. Significantly higher (p&lt;0.05) activities of amylase,malate dehydrogenase (MDH) and lactase dehydrogenase (LDH) were observed in all thetreatments compared with control. The outcomes of the present study indicate that crabmeal (31.5% CP) could be effectively utilised as a 50% replacement for fishmeal in the dietof E. suratensis advanced fry for higher yields. Keywords:Crab meal, Enzyme activity, Growth, Shrimp meal,Silkworm pupae meal

Responses of digestive enzyme profiles in newly-hatched (Zoea I) larvae of the mud crab Scylla serrata to intermittent food availability and food deprivation.

Activities (mU larva-1) of enzymes critical to digestion were examined to better understand how newly-hatched (Zoea I) larvae of the mud crab Scylla serrata respond to intermittent food availability and food deprivation. Specifically, this study examined the activities of trypsin-like proteases, nonspecific esterases, and α-amylase across three experiments that simulated scenarios in which larvae hatch and experience rearing conditions where food was either: (1) continuously available or unavailable; (2) initially unavailable, but subsequently available; or (3) initially available, but subsequently unavailable. Results showed that food availability exerts a significant influence on enzyme profiles in newly-hatched larvae, with nutritional history influencing their response to food deprivation. When food was unavailable from hatch, there was no significant change in larval enzyme activities between 6 and 78h post-hatch. If food became available at any point during this period, however, newly-hatched larvae were capable of rapidly (within 12-24h) adjusting enzyme activities in response. Furthermore, a short (36h) period of food availability appears sufficient to permit continuous substrate utilization during subsequent food deprivation of equivalent duration. Such flexibility is an important physiological strategy allowing newly-hatched larvae of S. serrata to adapt and thrive in challenging tropical oceanic environments and provides a basis for optimizing protocols for hatchery production of this species.

Nutritional innovations in superior gilthead seabream (Sparus aurata) genotypes: Implications in the utilization of emerging new ingredients through the study of the patterns of secretion of digestive enzymes

To promote sustainability and efficiency for aquaculture production, there are two key actions: i) The implementation of novel nutritional strategies with more sustainable raw materials, that aim to reduce the dependence on fishmeal (FM) and fish oil (FO) in the feeds, and ii) the implementation of a successful breeding program addressed to improve fish growth, feed utilization, and health. Different studies performed on salmonids and European sea bass (Dicentrarchus labrax) support the existence of genetic variability for the utilization of plant or non-marine-based diets. Nevertheless, those studies do not consider that the better zootechnical performance obtained in selected fish can be associated with differences in digestive biochemistry. Therefore, the present study aimed to evaluate the changes in the levels of the activities of different digestive enzymes present in two populations of gilthead seabream (Sparus aurata): reference or selected for high growth. Furthermore, the effect of different diets including a variety of protein ingredients partially substituting FM (poultry meal, insect meal, and bacterial single-cell protein) was assessed on the digestive enzyme profile of both fish genotypes, after 90 days of feeding. Higher levels of certain protein-related enzymes (pepsin and chymotrypsin) were found in selected sea bream fish compared with reference fish. Selected fish also revealed higher ADCs for dietary amino acids, irrespective of the diet fed, compared with the reference group. These results, added to the better growth and feed utilization of selected sea bream compared with reference fish, suggest that selected fish are more able to utilize the combination of emergent ingredients for aquafeeds, showing changes in the pattern of digestive enzymes to face the different ingredients in diets, which indicates a higher plasticity of the digestive enzymes to face changes in dietary ingredients. Those changes could be reflecting a compensatory mechanism to improve the digestibility of the ingredient.

Effect of feed supplementation with seaweed wracks on performance, muscle lipid composition, antioxidant status, digestive enzyme activities, and plasma biochemistry of gilthead seabream (Sparus aurata) juveniles

Macroalgal wracks are frequently considered as waste products. However, macroalgae are a rich source of protein and bioactive compounds with antioxidant and antimicrobial activities whose inclusion in aquafeeds is receiving growing attention. The aim of this study was to assess the use of beach-cast macroalgae as dietary supplement for gilthead seabream (Sparus aurata) juveniles. Fish were fed for 93 days with an extruded commercial diet (CD); a CD supplemented with 7% of a dried-powder from a multispecific macroalgal wrack (30.9% Lobophora sp., 21.9% Dictyota sp., 19.6% Asparagopsis taxiformis, 17.5% Cymopolia sp., 1.8% Hypnea sp., 0.2% Laurencia sp., 0.1% Stypocaulon sp., and 8% not determined) (CD+MU7); a CD supplemented with a monospecific macroalgal wrack of 85% Lobophora sp. (CD+MOL7); and a CD supplemented with a monospecific macroalgal wrack of 85% Dictyota sp. (CD+MOD7). Macroalgae were extracted with n-hexanes, ethyl acetate and ethanol, and the antioxidant capacity of extracts was assessed, with ethyl acetate leading to the most active extracts (p < 0.05). The dietary inclusions of a 7% macroalgal wrack did not negatively affect S. aurata survival, growth, body indexes, proximate composition, oxidative status and plasma parameters. Contrarily, fish fed on CD+MU7 and CD+MOD7 showed the highest monoacylglycerols content, while both monospecific diets led to the highest total saturated fatty acids content in muscle (p < 0.05). The digestive enzymes profile was slightly modified (p < 0.05), but without compromising fish performance. Finally, muscle from fish fed on CD+MOL7 seemed to display a better capacity to modulate the glutathione metabolism (p < 0.05). In conclusion, a 7% of macroalgal wracks can be used as a dietary supplement for S. aurata juveniles, depicting an attractive alternative for the effective harnessing of this usually discarded biomass. Macroalgal inclusion may also reduce the use of fish-based ingredients for aquafeeds, diminishing the pressure on pelagic fisheries, and contributing to the blue bioeconomy strategy.

Potential Symbiotic Effects of β-1,3 Glucan, and Fructooligosaccharides on the Growth Performance, Immune Response, Redox Status, and Resistance of Pacific White Shrimp, Litopenaeus vannamei to Fusarium solani Infection

The potential effects of dietary supplementation with β-1,3 glucan and fructooligosaccharides (β-1,3 GF) on antioxidant activities, immunological response, and growth performance of Pacific white shrimp (Litopenaeus vannamei) was investigated. Four diets (iso-energetic and iso-nitrogenous) with different levels of β-1,3 GF (0, 0.5, 1.0, and 1.5 g kg−1) were fed to healthy shrimp juveniles weighing 3 ± 0.5 g for 75 days. Shrimps were randomly distributed into 12 net enclosures at a density of 30 shrimp/net, and the experiment was performed in triplicate. The results revealed that long-term supplementation with 1.5 g kg−1 β-1,3 GF significantly improved shrimp weight gain, feed conversion ratio, and digestive enzyme profiles compared to the control diet group. However, there were no substantial variations in the contents of moisture, crude protein, total lipids, and ash in the muscles of shrimp fed on different diets. Surprisingly, all antioxidants (superoxide dismutase, catalase, glutathione peroxidase) and immune biomarkers (lysozyme, total hemocyte count, phenol oxidase, and respiratory burst) activities were significantly elevated with increasing levels of β-1,3 GF in the shrimp diet, and the highest values were recorded in the 1.5 g kg−1 diet groups. Challenge test results revealed that F. solani could cause a high mortality rate (86.7%) in a group fed a normal basal diet within 14 days at a dose of 5 × 104 conidia mL−1. Surprisingly, all dietary treated groups with different doses of β-1,3 GF showed high resistance against F. solani, represented by lower cumulative mortality rates (20–43.3%) compared to the control group. Moreover, most of the infected shrimp showed a typical black to brown gill lesion similar to that observed in the natural infection, where an identical fungus was successfully re-isolated from infected gills and muscles. Overall, this study recommends an appropriate incorporation level of β-1,3 GF that could enhance growth performance and improve the antioxidant activities, non-specific immunity, and disease resistance of L. vannamei, with an optimal level of 1.5 g kg−1.

Responses of digestive enzyme profiles to various scenarios of food availability in newly-hatched Stage I phyllosoma larvae of the tropical spiny lobster Panulirus ornatus

Stage I phyllosoma larvae of the spiny lobster Panulirus ornatus hatch in tropical oceanic waters with limited and variable food resources. To better understand how these larvae cope with food deprivation, this study examined specific (mU mg−1 protein) and total (mU larva−1) activities of major digestive enzymes (i.e., α-amylase, non-specific esterase, trypsin-like protease) during a series of ex situ experiments. Specifically, temporal changes in enzyme profiles were examined in three experiments simulating scenarios in which phyllosoma hatch and begin development in an environment where (1) prey is either continuously present or absent; (2) prey is initially present, but subsequently absent; (3) prey is initially absent, but subsequently present. Results indicated that the accessibility of suitable prey provides an overarching influence on digestive enzyme activities and substrate utilisation in Stage I phyllosoma of P. ornatus, with enzymatic responses to both intermittent prey availability and food deprivation being influenced by their nutritional history. In the absence of prey, larval digestive enzyme activities (mU larva−1) initially remained static from hatch but eventually declined with extended food deprivation. When prey became available, enzyme activities increased, with delayed access to prey having minimal impact on this enzymatic response. Furthermore, phyllosoma were able to adjust α-amylase and non-specific esterase activities (within 8 h) in response to the disappearance of prey, demonstrating adaptive changes to endure periods of food deprivation that were based on their nutritional history. The ability of phyllosoma to regulate enzyme activities from hatch is an important physiological strategy allowing them to survive in an environment characterised by highly variable zooplankton biomass and abundance, and explains why diets that differ greatly in nutrient composition have consistently been found effective for rearing phyllosoma in captivity.

Early performance, stress- and disease-sensitivity in rainbow trout fry (Oncorhynchus mykiss) after total dietary replacement of fish oil with rapeseed oil. Effects of EPA and DHA supplementation

Different vegetable oils have been investigated as potential substitutes of fish oil in aquaculture feed and several of them have proven to be successful in terms of fish growth rates, survival rates, biometric indices or feeding efficiency, even when used as the only oils in the feed. However, final fish product composition (fish whole body or fish fillet) usually reflects feed composition, and fish products from fish fed with only vegetable oils usually show a deficiency in long chain polyunsaturated fatty acids (PUFAs). The welfare and health consequences for the fish of these alterations of the fatty acid profile are not well known. In the current study, three experimental diets using supercritically defatted fish meal as well as rapeseed oil as a 100% replacement of fish oil, and differing in essential fatty acid (eicosapentaneoid acid - EPA, docosahexaenoic acid - DHA) supplementation, were tested in rainbow trout, Oncorhynchus mykiss. The growth performance, feed conversion ratio and digestive enzyme profiles were evaluated. Further, stress-and infection-challenge experiments were performed to assess the robustness of the fish against stress and disease. The trout fry fed the experimental diets showed a different fatty acid profile than fish fed a commercial diet, with lower EPA and DHA levels but higher linolenic acid (18:3n-3) and oleic acid (18:1n-9) levels. No significant effects were found in growth performance, feed conversion ratio or digestive enzymatic activity among diets. The fish stress responsiveness (brain and plasma stress marker response) to acute and repeated stressors was in general also similar irrespective of the diet. Infection trials, however, showed a differential ability of the fish to survive upon a controlled infection with the bacterium Flavobacterium psychrophilum. Fish fed with the experimental diets displayed higher mortalities than fish fed a commercial trout fry diet. The current results highlight the need of further research on nutritional requirements to optimize the disease resilience in farmed fish. These results also demonstrate that the adaptation of the fish to new formulated feed (in this case associated to plant oil ingredients) should not be assessed solely based on the growth performance of the fish. Other aquaculture relevant welfare indicators, as disease or stress resilience, should be part of a more complete assessment of feed adequacy for fish farming purposes.

Digestive enzymes profile of the midgut gland of juvenile painted river prawn (Macrobrachium carcinus)

This study assessed the activity of the main digestive enzymes in juveniles of the painted river prawn Macrobrachium carcinus. Prawns reared in 24 m2 tanks at a density of 10 individuals. m−2 for 45 days were fed a commercial diet with 40 % crude protein. A sample of 21 prawns with 2.92 ± 0.60 g and 27.87 ± 1.50 mm had their midgut glands (MG) dissected. Assays prospecting total proteolytic activity, total amylase, α-amylase, trypsin, chymotrypsin, β-galactosidase, agarase and lipase in the MG were performed. The activities of several aminopeptidase (alanine, arginine, glycine, histidine, isoleucine, leucine, proline and tyrosine aminopeptidase) were also evaluated. In addition, the effect of calcium (CaCl2) on trypsin activity was assessed. The following mean (± SD) activities were found: total proteolytic activity (8.00 ± 0.003 U.mg-1); total amylase (0.322 ± 0.002 U.mg-1); α-amylase (8.730 ± 0.008 U.mg-1); trypsin (12.7 ± 0.001 mU.mg-1); chymotrypsin (19.94 ± 0.0019 mU.mg-1); β-galactosidase (59.4 ± 0.18 U.mg-1); agarase (13.34 ± 0.15 U.mg-1) and lipase (0.019 ± 2.73 U.mg-1). Amongst aminopeptidases, only alanine, arginine, glycine and leucine aminopeptidase were found to be active. At concentrations from 5 to 90 mM, the activity of trypsin was not affected by CaCl2. Compared to other prawn species, M. carcinus has a wide range of digestive enzymes and a tendency towards greater use of animal protein. As studies on the digestive enzymes of juvenile prawns of the Macrobrachium genus are scarce, the present results represent basic data that may serve as a reference for future studies and also aid in the formulation of diets specific for this important group of crustaceans.

Effect of dietary lipid content and stocking density on digestive enzymes profile and intestinal histology of rainbow trout (Oncorhynchus mykiss)

The effect of both dietary lipid level and stocking density on digestive function was tested in young rainbow trout under culture conditions. Two dietary lipid levels (14 and 33%) and three culture densities (15, 30 and 40 kg/m3) were assayed in triplicate lots: L14/D15, L14/D30, L14/D40, L33/D15, L33/D30 and L33/D40. Intestinal activities of amylase, lipase, trypsin, chymotrypsin, total protease (at different pHs) as well as some biometric parameters such hepatosomatic index (HSI) and digestivesomatic index (DSI) as indicative of perivisceral fat accumulation, were determined after a 12-weeks experimental period. A histological study of intestine was carried on to evaluate changes in tissue architecture. Fish fed on higher lipid diets grew more and accumulated a higher amount of fat in perivisceral tissue, although higher stocking density reduced this trend. According to digestive capacity, higher lipid intake induced an activation of lipase activity that was not apparent when fish were held under the highest rearing density. By other hand, dietary lipids promoted a significant inhibition of protease activity in fish under high density conditions. These results seem to indicate a clear interaction between both variables. In this study, it was manifested a general effect of dietary lipids level and culture density on digestive profile. These interactions should be taken into account when foreseeing the digestive utilization of a commercial feed at different culture conditions to improve fish production.

Profiles of digestive enzymes of two competing planktivores, silver carp and gizzard shad, differ

Typically, studies in digestive physiology in fish focus on a few enzymes and provide insight into the specific processes of the enzyme in a targeted species. Comparative studies assessing a wide number of digestive enzymes on fishes that compete for food resources are lacking, especially in the context of an introduced species. It is generally thought that the invasive silver carp (SVC; Hypophthalmichthys molitrix) directly compete for food resources with the native gizzard shad (GZS; Dorosoma cepedianum) in waters where they coexist. We compared 19 digestive enzymes between SVC and GZS throughout a year and in two rivers in the Midwestern United States: Illinois River and Wabash River. All digestive enzymes analyzed were detected in both SVC and GZS in both rivers. However, the profiles of the digestive enzymes varied by species. Alkaline phosphatase, valine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase and N-acetyl-β-glucosaminidase were all much higher in SVC than in GZS. Differences between digestive enzyme profiles were also observed between rivers and months. This study demonstrates the utility of using an ecological approach to compare physiological features in fishes.

Replacement of fish oil with a DHA-richSchizochytriummeal on growth performance, activities of digestive enzyme and fatty acid profile of Pacific white shrimp (Litopenaeus vannamei) larvae

This trial was conducted to evaluate the effects of replacing dietary fish oil with Schizochytrium meal for Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Six test microdiets were formulated using Schizochytrium meal to replace 0 g/kg, 250 g/kg, 500 g/kg, 750 g/kg, 1000 g/kg or 1500 g/kg fish oil DHA. No significant differences were observed in survival, growth, final body length and activities of digestive enzyme among shrimp fed different diets (p > .05). No significant differences were observed in C20:5n-3 (EPA) in muscle samples (p > .05). C18:3n-3 and C20:4n-6 in muscle increased as Schizochytrium meal replacement level increased (p < .05). No significant differences were observed in C22:6n-3 (DHA) and n-3 fatty acids among shrimp fed diets that algae meal replaced 0 g/kg - 1000 g/kg of fish oil. Shrimp fed diet R150 had higher DHA content than other groups and had higher n-3 fatty acids than that of shrimp fed diets R50, R75 and R100 (p < .05). C18:2n-6, PUFA and n-6 fatty acids in muscle increased, while n-3/n-6 ratio decreased with increasing algae meal replacement level from 0 g/kg to 1000 g/kg (p < .05). In conclusion, Schizochytrium meal could replace 1500 g/kg fish oil DHA in the microdiets without negatively affecting shrimp larvae survival, growth and activities of digestive enzyme.

Digestive enzyme profiles from foregut contents of blue swimming crab, Portunus pelagicus from Straits of Johor, Malaysia

This study describes the digestive enzyme profiles from foregut contents of the blue swimming crab, Portunus pelagicus (L.), from Straits of Johor, Malaysia. Adult male (mature and immature) and female (ovarian maturation stages 1–4) blue swimming crabs were assayed for the presence of digestive enzymes (protease, trypsin, amylase and lipase) in the foregut. The results show that in some instances, significant differences in enzyme activities were observed between the sexes of P. pelagicus. Protease, trypsin, and amylase were detected in all gonad maturation stages, suggesting that crabs including immature males can readily digest dietary protein and carbohydrates, but not lipids. Trypsin (except for ovarian maturation Stage 4) and lipase (ovarian maturation Stage 4 and mature male only) activities were considerably higher than amylase, indicating that dietary proteins and lipids are more important than carbohydrates and, thus, suggests a carnivorous diet. In conclusion, the changes in enzyme activities between the different maturation stages and sexes reflect natural changes in diet and feeding abilities of P. pelagicus.

Comparison of time-restricted and ad libitum self-feeding on the growth, feeding behavior and daily digestive enzyme profiles of Atlantic salmon

Although it has been hypothesized that a predictable feeding regime in animals allows physiological variables to be adjusted to maximize nutrient utilization and, hence, better growth performance, the assumption has rarely been tested. This study compares the effects of time-restricted versus free access self-feeding on the growth, feeding behavior and daily digestive enzyme rhythms of Atlantic salmon (Salmo salar). In an experiment that lasted 6 weeks, fish (109.9 g) were divided into two groups: group 1 had free access to a self-feeder (FA); group 2 received three meals per day (2 h per meal) at dawn, midday and dusk via a time-restricted self-feeder (TR). At the end of the experiment, the fish were sampled every 3 h over a 24-h period. The results showed that the TR fish quickly synchronized their feeding behavior to the feeding window and their blood glucose showed a significant postprandial increase, while FA fish displayed no statistically significant rhythms (P>0.05). Pepsin activity of TR fish also showed a significant daily rhythm (P 0.05). In conclusion, the study failed to confirm a link between the entrainment of daily digestive enzyme profiles and growth performance, with the TR group showing comparatively poor blood glucose regulation.

Effect of cortisol and triiodothyronine bath treatments on the digestive enzyme profile and growth ofCatla catlalarvae during ontogenic development

Digestive enzyme profile is a good indicator of the nutritional and health status of the fish. The present investigation aims to evaluate the effect of exogenous bath treatment of hormones, cortisol and triiodothyronine, on the digestive enzyme activities and growth of carp Catla catla (Ham.) during ontogenic development. Catla larvae (4 days old) were given bath treatment with cortisol (hydrocortisone, 0.2 mg L−1), 3,5,3′-triiodothyronine (T3, 2.5 mg L−1) and a combination of cortisol and T3 for 30 min. Digestive enzyme profile was recorded on every third day and was continued for 30 days. Larvae were fed with live food for initial 14 days and then weaned to mix feeding of live food and prepared diet. Significantly (P < 0.05) higher amylase, total protease, trypsin, chymotrypsin, lipase, chitinase and chitinobiase activities were found in the hormone-treated groups compared to the control one during ontogenic development. Among the treated groups, amylase activity was highest in cortisol-treated larvae. Total protease, trypsin, chymotrypsin, lipase, chitinase and chitinobiase activities were significantly (P < 0.05) higher in larvae exposed at combined treatment of cortisol and T3 compared to the other two groups in most sampling days. Average length, weight and specific growth rate of treated larvae were higher compared to the control one. The combined bath treatment of cortisol and triiodothyronine influenced the digestive enzyme activities of catla larvae and thereby enhanced the growth at early developmental stage. This helps the larvae to overcome the problems associated with early developmental stage.

Characterization of digestive enzymes protease and alpha-amylase activities in the thick-lipped grey mullet (Chelon labrosus , Risso 1827)

Activities of pepsin, trypsin, chymotrypsin, alpha-amylase and lipase, as well as their optima and stability to pH and temperature, were determined in digestive extracts of thick-lipped grey mullet, Chelon labrosus, of three different sizes: Group 1 (45.2 ± 3.0 g), Group 2 (180.9 ± 4.2 g), and Group 3 (328.5 ± 43.3 g). SDS-PAGE zymograms were also used to assess the role of serine proteases in the digestive tract of C. labrosus. On the other hand, possible changes in the digestive enzyme profile of C. labrosus during development were observed, with a comparatively lower pepsin activity, higher activities of alkaline proteases and alpha-amylase and no lipase activity recorded in pre-adult specimens. It is suggested that these variations are linked to the changes in diet composition with age, moving from a partly carnivorous to a more herbivorous feeding habit.

Activities of digestive enzymes in relation to ingested natural food in three carp species of the Himalayan River Ladhiya, northern India

The present investigation was carried out to study gut content and accompanying digestive enzyme profiles of the three carp species, golden mahseer Tor putitora, snow trout Schizothorax richardsonii and hill trout Barilius barila. The fishes were captured from the River Ladhiya, Champawat district, Uttarakhand, northern India. The digestive tract length was on average 1.8 and 2.3 times longer than the body, while members of Bacillariophyceae, Chlorophyceae, Cyanophyceae and Zygnematophyceae made up 95.15% and 99.63% of gut content in the golden mahseer and snow trout, respectively. In hill trout, the digestive tract being only half the body length, gut content was insects (72.73%), eggs of aquatic organisms (22.73%) and nematodes (4.55%). Estimated gut enzyme activities demonstrated that amylase activity was significantly (P < 0.05) higher in golden mahseer and snow trout compared to hill trout, while total protease, trypsin and chymotrypsin activities were all significantly (P < 0.05) higher in the hill trout compared to other species. A strong co-relation was found among relative gut length, food composition and digestive enzyme activities of each species. This may guide the future formulation of feed to these important species of carps kept in farm.

Starch and lipid in diets for douradoSalminus brasiliensis(Cuvier 1816): growth, nutrient utilization and digestive enzymes

Carbohydrates and lipids are the major and cheaper non-protein energy sources for fish diets. This study aimed at determining ideal relationship between dietary starch and lipids and their influence on digestive enzyme profile of juvenile dourado. Trials were set up in a closed-loop system with controlled temperature, dissolved oxygen, pH and total ammonia. Experimental extruded diets formulated to contain different starch (St) to lipids (Lip) ratio (St : Lip = 0 : 1, 0.3 : 1, 0.7 : 1, 1.0 : 1, 1.4 : 1, 2.0 : 1, 2.3 : 1 to 3.3 : 1) were fed to juvenile dourado (3.34 ± 0.16 g) and stocked into 30 polyethylene tanks (330 L, 30 fish per tank) in a completely randomized design with unbalanced repetition (n = 3 or 4), in two daily meals (1000 and 1530) until satiation, for 95 days. Dietary starch contents higher than 145.2 g kg-1 (St : Lip > 1.0 : 1.0) hampered the performance of fish, but, paradoxically, the inclusion of carbohydrates in the diet elicited better utilization of dietary protein and energy by the species. Fish adapted digestive enzyme profile to dietary starch contents through increasing secretion of alkaline proteases and non-specific lipases, but secretion of amylase was not altered. Physiological responses show the limitation of species on the use of dietary carbohydrates.