Changes In Digestive Enzyme Activities Research Articles

Changes in Digestive Enzyme Activities during Larval Development of Spotted Seatrout (Cynoscion nebulosus)

The spotted seatrout (Cynoscion nebulosus)—an important commercial species—has a high potential for aquaculture in the Gulf of Mexico. To optimize its feeding during larval rearing, this study aims to evaluate the primary gastric (pepsin), intestinal (leucine aminopeptidase and alkaline phosphatase), and pancreatic (alkaline protease, trypsin, chymotrypsin, amylase, and lipase) enzyme activities from hatching to day 30. A multivariate analysis identified three digestive enzyme development stages during the spotted seatrout larval transformation. The first stage occurred between 1 (mean ± standard error (SE) = 1.73 ± 0.14 millimeter (mm) standard length (SL)) and 3 (2.14 ± 0.07 mm SL) days after hatching (DAH); a period of digestive stability showed the highest activity in amylase and bile salt-dependent lipase. The second stage (from 4 (2.53 ± 0.09 mm SL) to 20 (10.92 ± 0.51 mm SL) DAH) was a period of digestive transition, during which leucine aminopeptidase, chymotrypsin, and alkaline proteases were identified as the predominant enzymes from 4 to 5 DAH. In the third stage—a period of digestive stability—pepsin was the major enzyme that occurred between 25 (16.51 ± 0.81 mm SL) and 30 (25.91 ± 0.82 mm SL) DAH. These results indicate that the spotted seatrout larvae have a digestive system adapted to lipids and carbohydrates at the onset of feeding, with an immediate transition to protein digestion when exogenous feeding begins. Additionally, the digestive system of the spotted seatrout may be considered mature at 25 DAH. Further research is needed to elucidate the mechanisms of digestive tract development in the spotted seatrout larvae.

Mechanisms of Digestive Enzyme Response to Acute Salinity Stress in Juvenile Yellowfin Tuna (Thunnus albacares).

This study investigates the effect of a sudden change in salinity for 48 h on the digestive enzyme activity of juvenile yellowfin tuna. The treatment included a control salinity of 32‱ in natural seawater and an experimental salinity of 29‱. Acute stress experiments were carried out on 72 juvenile yellowfin tuna (646.52 ± 66.32 g) for 48 h to determine changes in digestive enzyme activity in different intestinal sections over time (0 h, 12 h, 24 h, 48 h). The activities of pepsin, trypsin, α-amylase, lipase, and chymotrypsin in the digestive organs (stomach, foregut, and pyloric ceca) of juvenile yellowfin tuna were measured. Pepsin and pancreatic protease in the experimental group were significantly lower than in the control group (p < 0.05). α-amylase showed a fluctuating trend of decreasing and then increasing, and its activity trend was pyloric ceca > foregut > stomach. The lipase activity of gastric tissues decreased at the beginning and then increased, reaching a minimum at 24 h (2.74 ± 1.99 U·g protein-1). The change of lipase in the pyloric ceca and foregut was increasing and then decreasing. The lipase activity trend was pyloric ceca > foregut > stomach. The chymotrypsin showed a decreasing and increasing trend and then stabilized at 48 h with a pattern of pyloric ceca > foregut > stomach. Similarly, the gut villi morphology was not significantly altered in the acutely salinity-stressed compared to the non-salinity-stressed. This study suggests that salinity may change the digestive function of juvenile yellowfin tuna, thereby affecting fish feeding, growth, and development. On the contrary, yellowfin tuna is highly adapted to 29‱ salinity. However, excessive stress may negatively affect digestive enzyme activity and reduce fish digestibility. This study may provide a scientific basis for a coastal aquaculture water environment for yellowfin tuna farming, which may guide the development and cultivation of aquaculture.

Ontogenetic changes in digestive enzyme activities of a common water flea

AbstractAlthough the nutritional demands of animals are known to differ between immature and mature stages and between neonates from different clutches in various organisms, little evidence has been accumulated to examine this possibility in crustacean zooplankters. To this end, we examined the five digestive enzyme activities related to assimilations of carbohydrates, lipids, amino acids and phosphorus in the neonates, immature and mature individuals of panarctic Daphnia pulex. We found that all the enzyme activities were higher at lower food levels, indicating that the activities increased with decreasing supplies of the nutritional substances relative to the demands. As expected, these enzyme activities changed ontogenetically. Beta‐glucosidase activities increased with age, especially at a high food level, while the opposite pattern was found for lipase activities. A decreasing trend with age was also found in the activities of arginine and alanine amino‐peptidase and alkaline phosphatase at a low food level. These results suggest that juvenile individuals require more lipids, amino acids and phosphorus relative to the requirements of adult individuals, while the opposite pattern was true for carbohydrates. We also measured the enzyme activities of the neonates born from the 1st and 2nd clutches of the maternal individuals. The results showed that most digestive enzyme activities differed significantly between the neonates from the first and second clutches depending on the food levels. The present study confirmed that the nutritional demands differ not only between mature and immature individuals in Daphnia pulex and suggests that the mature individuals invest nutrients and energy reserves differently to neonates of the different clutches depending on their nutritional conditions.

Changes in digestive enzyme activities during the early ontogeny of milkfish, Chanos chanos larvae.

Knowledge of the developmental ontogeny of the digestive system and nutritional requirements of marine fish larvae is a primary requisite for their successful rearing under an optimal feeding regime. In this context, we assessed the activity profile of key digestive enzymes viz., trypsin, chymotrypsin, leucine aminopeptidase, lipase, amylase, and alkaline phosphatase during the early ontogeny of milkfish, Chanos chanos (0 day, 3 days, 6 days, 9 days, 12 days, 15 days, 18 days, 21 days, 25 days, and 30 days post-hatch). Larvae for this study were obtained from the successful breeding of milkfish at ICAR-Central Institute of Brackishwater Aquaculture, India. Growth curves (length and weight) of the larvae indicated a positive morphological development under a standardized feeding regime that comprised Chlorella salina, Brachionus plicatilis, Artemia salina nauplii, and commercial weaning feed for different larval stages. With respect to protein digestion, the specific activity of pancreatic enzymes trypsin and chymotrypsin and intestinal brush border leucine aminopeptidase showed two peaks at 3 dph and 15 dph, following the introduction of rotifer and Artemia nauplii. Similar bimodal peaks were observed for alkaline phosphatase and amylase activities, with the first peak at 3 dph and the second peak at 18 dph and 21 dph, respectively. Whereas in the case of lipase, high activity levels were observed at 0 dph, 3 dph, and 18 dph, with subsequent decreases and fluctuations. Overall, as most of the enzymes were found to have peak activities at 15 to 21 dph, this period can be potentially considered as the developmental window for weaning larvae from live to formulated feeds in milkfish hatcheries.

Effect of Unpalatable Diets, Food Restriction and Saccharin-Adulterated Diet on Tryptic, Chymotryptic, and Amylolytic Activity in Pancreas, Intestine and Feces of Rats

Growing rats were fed either 10 or 17% protein (casein) diets whose taste was changed daily by addition of aversive stimuli. Under these circumstances food intake and body weight gain were reduced compared with controls fed unadulterated diets. More amylolytic activity per gram pancreas was found in rats fed a 10% protein, aversive diet and in their pair-fed controls fed restricted amounts of an unadulterated diet compared with ad libitum controls. More amylolytic activity per gram chyme of small intestine was also found in rats fed less than ad libitum amounts of a 10% protein diet. The chymotrypsin activity in the pancreas of rats fed a 17% protein, aversive diet was greater than in that of control animals or that of the pair-fed animals. The 2- to 10-fold higher proteolytic activity found in the small intestine and especially in the large intestine and feces of rats fed the aversive diet was specificially related to the adulteration of the diet with sodium saccharin. Feeding a diet containing sodium saccharin led to lower cecal pH. Under conditions of the present experiments, changes in digestive enzyme activity are not directly related to the aversive taste of the diet.aversive taste unpalatable diets food restriction saccharin trypsin chymotrypsin amylase

Editorial Comment on the Highlight Article “Ontogenetic changes in digestive enzyme activity and biochemical indices of larval and post larval European lobster (Homarus gammarus, L)” by Renata Goncalves et al.

Editorial Comment on the Highlight Article “Ontogenetic changes in digestive enzyme activity and biochemical indices of larval and post larval European lobster (Homarus gammarus, L)” by Renata Goncalves et al.

Determination of Digestive Enzyme Activity in Gilt-Head sea bream (Sparus aurata ) Feeding with Commercial Feed

With the increase in the world population, aquaculture has a very important place in meeting the protein needs of humanity. Today, fish farming is developing rapidly depending on the increase in demand. Fish is one of the most important foodstuffs for human nutrition. Studies on the quality and characteristics of the feeds used gain importance with the increase in the knowledge about the nutrient sources of fish. It is known that there is a linear correlation between growth, productivity and feed efficiency in fish like another animal. At this point, the correct and effective use of feed, which is the most important input in production, is very important in terms of increasing the yield and product quality to be obtained from the product and reducing production costs. The identification of digestive enzyme activities is important in developing new feeding regimens and in ensuring optimal growing conditions. As most enzymes regulate the events of viability, the increase or decrease in their activity causes the degradation of the normal functions of fish and diseases in fishes. In this study, body weight and changes in digestive enzyme activity were investigated in sea bream feeding with commercial feed. For this purpose, a total of 3000 juveniles with an initial mean weight (IW) of 2.72±0.78 g were divided into 4 tanks (2000 L). After the six weeks final weight was 7.75 ± 0.67 at the end of experiment. While trypsin activity was increased until the end of the experiment, amylase activity was decreased. On the other hand, small decreases in lipase activity were observed throughout the experiment.

Ontogenetic changes in digestive enzyme activity and biochemical indices of larval and postlarval European lobster (Homarus gammarus, L)

Ontogenetic changes in digestive enzyme activity and biochemical indices of larval and postlarval European lobster (Homarus gammarus, L)

Persistence of Digestive Enzyme Activities of Sea Cucumber (Apostichopus japonicus): Evidence From Diet Switch After Evisceration

A two-stage diet-switch experiment was conducted to examine the hypothesis that the changes in digestive enzyme activities of sea cucumber (Apostichopus japonicus) induced by historic diets might persist in the regenerated intestines. In stage I, A. japonicus were treated with two different diets for 56 days, including diet A with 11% crude protein, 1% crude lipid, and 40% carbohydrate, and diet B with 18% crude protein, 2% crude lipid, and 35% carbohydrate. In stage II, each treatment was subjected to evisceration with 0.35M KCl or not (eviscerated and non-eviscerated groups), half of which were then switched to different diets from diet A to B or vice versa for 112 days. The persistence of digestive enzyme activities was evaluated by measuring the changes in digestive enzyme activities before and after evisceration. In stage I, diets B and A increased trypsin and amylase activities, respectively. In stage II, the higher trypsin activities were observed in eviscerated and non-eviscerated A. japonicus that had consumed diet B in stage I. The higher amylase activities were observed only in eviscerated A. japonicus that had consumed diet A in stage I. It indicated that the historic diets showed long-term effects on the digestion of A. japonicus, which led to the persistence of changes in both trypsin and amylase activities in intestines, especially in the regenerated intestines. In addition, the specific growth rates (SGRs) and metabolic rates (MRs) of A. japonicus were affected by the long-term effects of historic diets. Meanwhile, the relationships between enzymic activities, SGRs, and MRs were observed in A. japonicus, indicating that the historic diets could produce long-term effects on the growth and metabolism of A. japonicus through their long-term effects of historic diets on digestive enzyme activities. In conclusion, the present study showed that the changes in digestive enzyme activities induced by different diets in stage I could persist in the intestines and regenerated intestines, leading to long-term effects of historic diets on the growth and metabolism of A. japonicus.

Feeding regimes affected the circadian rhythms of pancreatic digestive enzymes and somatic growth in flathead grey mullet (Mugil cephalus) fry

The effect of different feeding regimes on the circadian rhythms of pancreatic digestive enzyme activities was evaluated in Mugil cephalus fry weighting 0.34 ± 0.01 g. Feeding regimes (feeding ration = 3% stocked biomass) differed on the number of meals offered per day: one, two and ten meals per day (R1, R2 and R3, respectively). The number of meals per day affected somatic growth; in particular, fry from the R3 group (0.80 ± 0.01 g) grew better than their congeners from R2 (0.70 ± 0.01 g) and R1 (0.63 ± 0.01 g) groups (P < 0.05). Feeding behaviour was modulated by the feeding regime, being the maximal gut fullness values found just after meal distribution in R1 and R2 groups, whereas this trend was not observed when feed was offered continuously during light hours (R3). Fry from R1 and R2 groups showed hyperphagia as they tended to store in their gut as much as possible feed particles to be later digested due to the limited daily meals. This strategy negatively affected feed digestion due to inappropriate enzyme to substrate ratio, changes in digestive enzyme activities and chyme transit times, which ultimately impaired growth performance. Enzyme activities were modulated by the number of meals, the more frequent the meals offered, the lower enzyme activities, supporting the hypothesis that digestive function is adapted to obtain a maximum benefit of the ingested nutrients. Present results showed that feeding grey mullet fry continuously during day light hours optimized feed digestion and promoted fry growth.

Ontogenetic variation in digestive enzyme activities within embryos and newly-hatched larvae of the tropical spiny lobster, Panulirus ornatus

While there is considerable interest in aquaculture of spiny lobsters (Palinuridae), limited knowledge of nutritional requirements during early life stages remains a major impediment to successful hatchery culture. To better determine endogenous nutrient utilisation during the early life stages of the tropical spiny lobster, Panulirus ornatus, we examined ontogenetic variation in digestive enzyme activities within developing embryos and newly-hatched phyllosoma in the absence of an exogenous food source. Specifically, α-amylase, non-specific esterase, and trypsin-like protease activities were quantified to indicate the relative importance of macronutrients (i.e., carbohydrate, lipid, and protein) and gauge the digestive potential of newly-hatched phyllosoma during transition from endogenous to exogenous nutrient sources. Ontogenetic variation in digestive enzyme activities indicated that lipid, protein, and carbohydrate were sequentially utilised by embryos. Early increase in non-specific esterase activity suggests that lipid is the most critical macronutrient for early embryonic development, with protein and carbohydrate becoming increasingly utilised shortly before and after hatching. The observed peak in trypsin-like protease activity during the first day post-hatch presumably allows phyllosoma to make best use of dietary items that are high in protein at first-feeding. In the absence of an exogenous food source after hatching, changes in digestive enzyme activities suggest that a metabolic shift from protein to lipid occurred, coinciding with the timing of the ‘point-of-no-return’ for Stage I phyllosoma of P. ornatus. Our results highlight the importance of providing an exogenous protein-rich food source to phyllosoma soon after hatch and provide a foundation for further study into broodstock nutrition and egg quality of this species.

Role of digestive enzymes in the adaptation of Frankliniella occidentalis to preferred and less‐preferred host plants

AbstractThe western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important invasive pest that causes serious damage to vegetables in China. Changes in digestive enzyme activities (α‐amylase, trypsin, and tryptase) and gene expression levels of F. occidentalis were examined after they were transferred to kidney bean, a preferred host, or broad bean, a less‐preferred host. The results showed that α‐amylase and trypsin activities initially decreased in both nymphs and adults after transfer to kidney bean or broad bean plants and they were the lowest in the F1 generation. The α‐amylase and trypsin activities were significantly different among the tested generations. The tryptase activities in the second instars fed on kidney bean plants were not significantly different from those of the controls in nymphs at all three generations, whereas they increased when fed on broad bean plants. Most digestive enzyme genes in both the nymph and adult thrips showed similar changes, decreasing with transfer to kidney bean plants and increasing on broad bean plants. However, the expression levels of the trypsin gene FoTRYP‐1 and the tryptase gene FoTPSB2 in the second instars fed on broad bean and kidney bean plants, respectively, were not significantly different from those of the controls. The expression levels of the four digestive enzyme genes were significantly higher in broad bean than in kidney bean plants. These results indicate that F. occidentalis can adjust its digestive enzyme activities and gene expression levels after being transferred to host plants for which its preference differs and that the changes depend on the specific enzyme, thrips generation, and developmental stage. Findings from this study would provide a basis for further studies to reveal the physiological and ecological bases of the wide host range and strong host adaptability of F. occidentalis.

Changes in digestive enzyme activities during the early ontogeny of the South American cichlid (Cichlasoma dimerus).

Cichlasoma dimerus is a neotropical cichlid that has been used as a biological model for neuroendocrinology studies. However, its culture is problematic in terms of larval feeding to allow having enough fry quantity and quality. Larviculture requires full knowledge about the digestive system and nutrition; therefore, this study was intended to assess the digestive enzymes' changes at different ages during the early ontogeny. Acid protease activity was detectable from the first day after hatching (dah), increasing to its maximum peaks on 9 dah. In contrast, alkaline proteases had low activity in the first days of life but reached their maximum activity on 17 dah. Chymotrypsin, L-aminopeptidase, and carboxypeptidase A activities increased at 6 dah, while trypsin activity was first detected on 13 dah and reached its maximum activity on 17 dah. Lipase and α-amylase activity were detectable at low levels in the first days of life, but the activity fluctuated and reaching its maximum activity at 21 dah. Alkaline phosphatase continued to oscillate and had two maximum activity peaks, the first at 6 dah and the second at 19 dah. Zymograms of alkaline proteases on day 6 dah six revealed four activity bands with molecular weights from 16.1 to 77.7kDa. On 13 dah, two more activity bands of 24.4 and 121.9kDa were detected, having a total of six proteases. The enzymatic activity analyzes indicate the digestive system shows the low activity of some enzymes in the first days after hatching, registering significant increases on 6 dah and the maximum peaks of activities around at 17 dah. Therefore, we recommend replacing live food with dry feed and only providing dry feed after day 17 dah.

Activities of digestive enzymes and non-specific immune indicators in &amp;lt;italic&amp;gt;Diodon holocanthus&amp;lt;/italic&amp;gt; during larval and juvenile stages

In order to solve the problem of high mortality rate of longspined porcupinefish <italic>Diodon holocanthus</italic> larvae and juveniles, the changes in digestive enzyme activities and non-specific immune indexes from the newly-hatched larvae to juveniles (0-40 d) were studied. The relationship between total length and daily age of <italic>Diodon holocanthus</italic> larvae and juveniles could be fixed to the exponential functions. The activities of amylase, pepsin, trypsin, and lipase were identified in the newly- hatched larvae. During the whole experiment period, the amylase and trypsin activities showed a trend of increasing initially, followed by a decreasing, but then increased again(with the increased daily age), in which amylase activity reached the maximum at 20 d, trypsin activity reached the peak at 5 d, the overall activity of both increased with the daily age but the trypsin activity increased more obviously. Lipase activity decreased rapidly initially (1-5 d), followed by an significant increase (5-10 d), but then decreased drastically again(15-20 d) and maintained at a low level. The activity of pepsin increased gradually from 1 d to 15 d and reached the maximum at 15 d, after which it slowly reduced to the minimum. The activity of lysozyme (LZM) and immunoglobulin M(IgM) showed a trend of increasing first and then decreasing, in which immunoglobulin M activity reached the maximum at 10 d, while lysozyme reached the maximum at 5 d, and after that both decreased slowly and fluctuated and eventually remained at a low level. The above results indicated that the changes of digestive enzyme activities in the larvae and juveniles of <italic>Diodon holocanthus</italic> were closely related to their developmental stages and food types, and various digestive enzyme activities existed in newly-hatched larvae that had not yet eaten food. The non-specific immune indicators increased significantly during the mixed nutrition period when the larvae and juveniles of <italic>Diodon holocanthus</italic> transitioned from endogenous nutrition to exogenous nutrition, and then decreased slowly to a lower level, indicating that the nutritional transformation process had a greater impact on the immune function of larvae and juveniles, higher non-specific immune indicators increased the disease resistance of larvae and juveniles and enhanced the survival rate of breeding.

Changes in digestive enzyme activities during early ontogeny of Seriola rivoliana.

This study contributes to basic knowledge on the development of larval digestive enzyme activities of Seriola rivoliana, a carnivorous species that has shown high mortality in larval stage. The study was conducted under laboratory-controlled conditions until larvae reached 30days after hatching (DAH). The specific activity of amylase and pepsin was analysed by spectrophotometric methods, and lipase, trypsin, chymotrypsin and alkaline phosphatase by fluorometry. The results showed that S. rivoliana larvae had different enzyme patterns depending on their developmental stage, and also when exogenous food was administered (rotifers and Artemia). At hatching (2.98 ± 0.14mm SL), lipase, alkaline phosphatase, trypsin and chymotrypsin activities were detected, but the last two enzymes showed an activity close to zero. Trypsin, chymotrypsin, lipase and alkaline phosphatase sharply increased their activities after starting the first feeding. Amylase activity was not detected until 5 DAH (3.51 ± 0.18mm SL) and had a peak on day 15 (4.59 ± 0.39mm SL); no activity was observed from then on. Pepsin activity was detected approximately at 15 DAH, showing a constant increase onwards. Trypsin had a peak on day 15 and then decreased on the following days. Chymotrypsin had the highest peak at 5 DAH, then a sharp decrease on day seven (3.88 ± 0.11mm SL), and it increased gradually until day 30 (11.71 ± 1.59mm SL). Lipase showed the highest activity at 15 DAH and then decreased its value. Finally, alkaline phosphatase showed the highest value at 3 DAH (3.62 ± 0.06mm SL); then, a severe decrease was observed with activity stability on the following days. In conclusion, S. rivoliana larvae had a similar pattern as that observed in other marine-carnivorous fish larvae, so it could be considered as juvenile at 20 DAH in terms of digestive physiology; based on our results and previous study, the weaning process could start after this age, which would allow establishing a co-feeding protocol using inert diet.

Changes in digestive enzyme activities during different developmental stages of the crayfish Astacus leptodactylus Eschscholtz, 182

The present study determined changes in protease, α-amylase and lipase activities during embryonic and post-embryonic developmental stages of the freshwater crayfish &lt;em&gt;Astacus leptodactylus&lt;/em&gt; Eschscholtz, 1823. The embryonic stages studied comprised Phase III (blastula formation), Phase X (embryos with anlagen of masticatory) and Phase XIV (embryos with strongly developed posterior hepatopancreas lobes). The post-embryonic stages comprised Stage I (no feeding) and Stage II (prior to the onset of feeding). Protease and α-amylase activities were relatively high as compared with lipase activity. Protease activity values showed a steady increase from Phase III to Stage I. α-amylase and lipase activities were low in Phase XIV. The activities of these two enzymes tended to increase just before hatching and reached the highest levels in Stage II. Digestive enzyme activities increased in accordance with maturation of the hepatopancreas and prior to the onset of external feeding. Protease activity was high in the early stage of embryonic development and continued to increase in later stages. On the other hand, α-amylase and lipase activities were low until maturation of the hepatopancreas and then remained high. The results of the present study provide important information on changes in digestive enzyme levels during different developmental stages of &lt;em&gt;A. leptodactylus&lt;/em&gt;.

Changes in digestive enzyme activities and nutrient utilization during embryonic development and starvation of newly hatched larvae of the mud crab, Scylla serrata

One of the most important yet poorly understood components of hatchery production of crustaceans is larval nutrition and digestive capacity. Larvae of aquatic animals, particularly early larvae, rely primarily on chemical digestion of ingested foods using enzymes. This study assayed the major digestive enzymes of the mud crab, Scylla serrata, during embryonic development and after various periods of starvation of the newly hatched larvae, to assess larval capacity to digest major nutrients and to evaluate the relative utilization of these nutrients for energy production. Lipids were the first energy reserves utilized during the early periods of embryonic development as indicated by the early significant increase in esterase activity compared to the relatively low and steady levels of amylase and protease activities. As readily available lipid reserves were depleted, and became insufficient to meet the increasing energy demands towards the end of embryonic development, protein and, to some extent carbohydrates, were increasingly utilized. This was demonstrated by the levelling of esterase activities, coinciding with significant increases in protease and esterase activities towards the final phase of embryonic development. Starved newly-hatched S. serrata larvae continued to utilize mostly proteins as indicated by relatively high protease activities compared to amylase and esterase activities. Persistent high protease activity in starved S. serrata larvae, suggested degradation of structural proteins, implying the need to immediately feed newly hatched larvae. These results highlight the significance of lipid reserves in developing embryos of S. serrata, and the importance of appropriate broodstock nutrition and management to ensure that these reserves are accumulated sufficiently to produce high quality eggs and larvae.

Developmental changes in digestive enzyme activity in American shad, Alosa sapidissima, during early ontogeny.

In order to assess the digestive physiological capacity of the American shad Alosa sapidissima and to establish feeding protocols that match larval nutritional requirements, we investigated the ontogenesis of digestive enzymes (trypsin, amylase, lipase, pepsin, alkaline phosphatase, and leucine aminopeptidase) in larvae, from hatching to 45days after hatching (DAH). We found that all of the target enzymes were present at hatching, except pepsin, which indicated an initial ability to digest nutrients and precocious digestive system development. Trypsin rapidly increased to a maximum at 14 DAH. Amylase sharply increased until 10 DAH and exhibited a second increase at 33 DAH, which coincided with the introduction of microdiet at 30 DAH, thereby suggesting that the increase was associated with the microdiet carbohydrate content. Lipase increased until 14 DAH, decreased until 27 DAH, and then increased until 45 DAH. Pepsin was first detected at 27 DAH and then sharply increased until 45 DAH, which suggested the formation of a functional stomach. Both alkaline phosphatase and leucine aminopeptidase markedly increased until 18 DAH, which indicated intestinal maturation. According to our results, we conclude that American shad larvae possess the functional digestive system before mouth opening, and the significant increases in lipase, amylase, pepsin, and intestinal enzyme activities between 27 and 33 DAH suggest that larvae can be successfully weaned onto microdiets around this age.

Ontogenetic changes in digestive enzyme activities and the amino acid profile of starry flounder Platichthys stellatus

Ontogenetic changes in digestive enzyme activities and the amino acid (AA) profile of starry flounder, Platichthys stellatus, were investigated and limiting amino acids were estimated compared with the essential AA profile between larvae and live food to clarify starry flounder larval nutritional requirements. Larvae were collected at the egg stage and 0, 2, 4, 7, 12, 17, 24 days after hatching (DAH) for analysis. Larvae grew from 1.91 mm at hatching to 12.13 mm at 24 DAH. Trypsin and chymotrypsin activities changed slightly by 4 DAH and then increased significantly 4 DAH. Pepsin activity increased sharply beginning 17 DAH. Lipase activity increased significantly 4 DAH and increased progressively with larval growth. Amylase activity was also detected in newly hatched larvae and increased 7 DAH followed by a gradual decrease. High free amino acid (FAA) content was detected in starry flounder eggs (110.72 mg/g dry weight). Total FAA content dropped to 43.29 mg/g in 4-DAH larvae and then decreased gradually to 13.74 mg/g in 24-DAH larvae. Most FAAs (except lysine and methionine) decreased >50% in 4-DAH larvae compared with those in eggs and then decreased to the lowest values in 24-DAH larvae. Changes in the protein amino acid (PAA) profile were much milder than those observed for FAAs. Most PAAs increased gradually during larval development, except lysine and phenylalanine. The percentages of free threonine, valine, isoleucine, and leucine decreased until the end of the trial, whereas the protein forms of these four AAs followed the opposite trend. A comparison of the essential AA composition of live food (rotifers, Artemia nauplii, and Artemia metanauplii) and larvae suggested that methionine was potentially the first limiting AA. These results may help develop starry flounder larviculture methods by solving the AA imbalance in live food. Moreover, the increased digestive enzyme activities indicate the possibility of introducing artificial compound feed.

Changes in digestive enzyme activities during larval development of Chinese loach Paramisgurnus dabryanus (Dabry de Thiersant, 1872).

The digestive physiology of Chinese loach (Paramisgurnus dabryanus) was studied by assessing the specific and total activities of different pancreatic (trypsin, chymotrypsin, amylase and lipase), gastric (pepsin) and intestinal (alkaline phosphatase and leucine-aminopeptidase) enzymes from hatching to 40 days after hatching (DAH). Larvae were reared at 24.4 ± 0.4 °C and fed with rotifers from mouth opening (4 DAH) to 15 DAH, from 10 to 35 DAH with Cladocera and from 30 to 40 DAH with compound diet. Enzyme activities for trypsin, chymotrypsin, amylase and lipase were detected before the onset of exogenous feeding, indicating that these enzymes were genetically pre-programmed. Most of the pancreatic enzyme specific activities increased until 20 DAH and decreased thereafter. The pepsin activity of Chinese loach was firstly detected at 30 DAH, indicating the appearance of functional gastric gland. Alkaline phosphatase specific activity was detected from hatching onward, showed marked increase and reached the second peak at 20 DAH, while a gradual increase in specific leucine-aminopeptidase activity was observed until the end of the experiment. Accordingly, the larvae of Chinese loach possess a functional digestive system before the onset of exogenous feeding and the digestive capacity gradually increases as development progresses. The abrupt increase in intestinal enzyme activities between 10 and 20 DAH demonstrates onset of juvenile-like digestive mode in Chinese loach larvae. The increase in pepsin activity after 30 DAH indicates the shift from alkaline to acidic digestion in Chinese loach larvae, which may be considered as the onset of weaning.