Effect of fish feed processing conditions on digestive protease activities, free amino acid pools, feed conversion efficiency and growth in Atlantic salmon (Salmo salar L.)

The responses of the digestive proteases trypsin and chymotrypsin and protein metabolism to differences in feed protein quality were investigated in Atlantic salmon (Salmo salar L.). Two sets of experimental feeds were produced. Each set of high and low quality feeds was provided to either 150 g or 2 kg salmon. Protein in the high quality feeds had significantly higher percentages of free (reactive) sulphydryl (SH) groups than the corresponding feeds based on low quality meals. After 90 days feeding, groups given high and low quality feeds did not differ in their specific growth rates (SGR) in either experiment. However, feed conversion efficiency (FCE) was significantly different between the high and low quality feed groups in 2 kg salmon, where the difference between the high and low feed protein qualities was larger, 10% versus 4% SH/[SH + (S–S)] in 150 g salmon. Higher FCE was preceded by significantly higher trypsin and chymotrypsin specific activities on day 60. SGR, in general, changed after the first month and was stable during the last 2 months in both experiments. Concurrently, both trypsin (T) and chymotrypsin (C) decreased with an increased activity ratio of trypsin to chymotrypsin (T/C ratio), and resulting in significantly lower T/C ratio on day 90 in salmon feeding on high quality feeds in both sizes of fish. Differences in FCE were associated with significant differences in levels of total free amino acids (TFAA) in the plasma and the white muscle, as well as in the ratio of essential to non‐essential free amino acids (EAA/NEAA ratio), free hydroxyproline, and RNA in the white muscle. Interestingly, after 3 days starvation (day 93), 5–7 h postprandial EAA/NEAA ratio in the plasma was significantly lower in the high quality diet groups in both experiments. Trypsin specific activity inversely correlated with muscle TFAA levels in 2 kg salmon, concurrent with higher muscle levels of RNA, lower free hydroxyproline and higher FCE in fish fed higher quality diets.     

The effect of feeding on the secretion of pepsin,trypsin and chymotrypsin in the Atlantic salmon,Salmo salar L

Pepsin stored in the stomach mucosa of the Atlantic salmon (Salmo salar L.) increases within two days of the onset of starvation. Trypsin and chymotrypsin in the pyloric caeca/pancreas behave similarly, indicating that when no food is present in the gut, digestive enzymes accumulate in the secretory tissues. As a corollary, trypsin and chymotrypsin activities in the gut contents fell during starvation, indicating that secretion is greatly reduced when food is not present. At the onset of feeding, pepsin is rapidly synthesised in the mucosal tissues and then secreted. Twenty four hours after feeding, the pepsin levels of the mucosa are still low, suggesting that synthesis may be a rapid response to the presence of food in the stomach. Secretion of trypsin and chymotrypsin appears to take place as soon as digesta enters the intestine, between 4 and 14h after feeding, and resynthesis of enzyme precursors appears to be complete again within a further 11h. It is suggested that both synthesis and release may be under the control of cholecystokinin.     

Digestive efficiency,free amino acid pools and quality of growth performance in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) affected by light regimes and vaccine types

This study comprised the results of three different seawater trials using unique combination of techniques to study protease digestive efficiency and growth performance quality to illustrate the effects of light regimes and vaccine types in Atlantic salmon (Salmo salar L.). Fish with higher growth had higher trypsin (T) and chymotrypsin (C) specific activities with higher T/C ratio or slope T/C ratio [calculated from the regression between trypsin (y) and chymotrypsin (x) specific activities] in the pyloric caeca. The T/C ratios indicated fish growth rates over a period of 1–2 months, while the slope T/C ratios indicated fish growth rates at sampling. Adaptation period for adjustment to the new environment of continuous light was 70 days, indicated by the differences in trypsin specific activities and the crossing of slope T/C ratio regressions following with the changes in growth rate directions between the control and the treated group. Vaccine types affected fish vertebral growth, and additional continuous light enhanced the impact of vaccines on fish growth during springtime, indicated by differences in slope T/C ratios. Continuous light stimulated fish growth during winter to spring, when the natural day length was short, without significantly changing white muscle and oocyte qualities in the fish of about 500 g, except for significantly increased white muscle RNA concentration. Continuous light also reduced fish growth rate later during summer, when the natural day length was long, by precedently decreasing the T/C ratio in late spring. Interestingly, plasma levels of free lysine related to tryptic digestion were correlated with trypsin specific activity levels. Continuous light caused higher levels of most free amino acids (FAA) involved in nitrogen metabolism, higher incorporation of essential FAA for protein synthesis, and higher protein turnover rate (free hydroxyproline levels) in both plasma and white muscle. However, continuous light did not affect higher protein content, intracellular buffering capacity and RNA levels in the white muscle of the fish of about 1 kg, probably due to limitation of FAA available for protein synthesis. It is therefore suggested that enhancing fish growth by continuous light stimulation should be accompanied by increasing availability or content of dietary protein (and probably minerals), which in turn would improve the quality of fish growth performance through increasing fillet protein concentration, strengthening vertebral growth, and delaying oocyte development.     

Digestive protease activities and free amino acids in white muscle as indicators for feed conversion efficiency and growth rate in Atlantic salmon (Salmo salar L.)

The aim of the present experiment was to screen several biochemical indices in fish and their interrelations in order to select variables for future studies of growth rate and feed conversion. Several parameters [trypsin activity, chymotrypsin activity, free amino acids (FAA) in plasma and white muscle, and RNA and RNA/protein ratio in the white muscle] were measured together with specific growth rate (SGR), feed intake and feed conversion efficiency (FCE) in four groups of diploid or triploid Atlantic salmon (Salmo salar L.) reared under different light regimes. SGR was measured on individually tagged fish, whereas feed intake and feed conversion was estimated on tank basis. A principal component analysis (PCA) explained 80.6% of the variance in the data, using all measured parameters, regardless of ploidy and light regime. Muscle free hydroxyproline showed the highest correlation, alone explaining 55% of SGR variability. The SGR also significantly correlated with trypsin activity (r=0.34), the activity ratio of trypsin to chymotrypsin (T/C) (r=0.39), plasma essential FAA (EAA) (r=0.39), plasma total FAA (TFAA) (r=0.37), the ratio of essential to non-essential FAA (EAA/NEAA) in the white muscle (r=–0.45), muscle RNA (r=–0.45) and RNA/protein ratio (r=–0.41). Tank FCE correlated positively (r=0.97) with SGR, T/C ratio and muscle free hydroxyproline, and negatively (r=–0.90) with muscle EAA/NEAA. The groups reared under continuous light (LL) regime showed significantly higher SGR than simulated natural photoperiod (SNP) groups, and with an apparently higher FCE. A higher growth rate was associated with either a higher consumption rate and/or a higher feed utilization. A negative correlation between muscle RNA concentration and SGR may indicate that increased growth rate under LL regime was not caused by an increased protein deposition rate.     

Do digestive enzymes set a physiological limit on growth rate and food conversion efficiency in the Atlantic cod (Gadus morhua)?

The objective of this study was to determine the potential sites of maximal growth limitation in Atlantic cod (Gadus morhua). Forty cod were reared in ten sea water tanks. Fish were randomly divided into 5 groups, a control group (injected with saline solution) and 4 experimental groups that received different levels of recombinant bovine somatotropin (rbST: 1.0, 2.0, 4.0 and 10.0 g g fish^–1 2 weeks^–1) by injection in the abdominal cavity. Fish were fed ad libitum 3 times a week during four weeks. We measured individual body mass, growth rate, food intake and food conversion efficiency. At the end of the experiment, we measured the activity of acid proteases in the stomach; trypsin and chymotrypsin in the pyloric caeca; alkaline phosphatase (ALP) and glutamyltransferase (GGT) in the intestine. No significant differences were observed in growth rate, food intake or food conversion efficiency among the five groups. Trypsin, chymotrypsin, ALP and GGT activities when expressed in U g fish^–1 were correlated with growth rate. These enzymes were also correlated with food ingestion except for trypsin when expressed in U mg protein^–1. Trypsin was the only enzyme that showed a significant correlation with food conversion efficiency. Our conclusion is that, at the level of digestion, trypsin is the only enzyme measured that could be suspected to potentially limit growth rate in cod.     

Digestive proteinases and peptidases in the hepatopancreas of the southern brown shrimp (Farfantepenaeus subtilis) in two sub‐adult stages

The aim of this study was to examine proteinases and peptidases from the hepatopancreas of two sub‐adult stages of Farfantepenaeus subtilis: SAS₆ (5.93 ± 0.69 g wet weight) and SAS₁₃ (13.26 ± 0.60 g wet weight). Trypsin and chymotrypsin activity was higher in the extract from the SAS₆ individuals (P < 0.05). The highest activity among aminoacyl‐β‐naphthylamide substrates was found using alanine‐, arginine‐, leucine‐ and lysine‐β‐naphthylamide. There was a positive correlation between the recommended concentration of essential amino acids in penaeid shrimp feed and aminopeptidase activity in both sub‐adult stages. Proteolytic activity of F. subtilis was strongly inhibited by specific trypsin inhibitors. The optimal temperature for trypsin, chymotrypsin and leucine aminopeptidase activity was between 45 and 55 °C. Six and seven bands were found in caseinolytic zymograms for SAS₆ and SAS₁₃ respectively. All bands were inhibited by phenylmethylsulfonyl fluoride in both sub‐adult stages. The use of tosyl‐lysine‐chloromethyl‐ketone and benzamidine caused strong inhibition of the proteolytic bands. Trypsin and chymotrypsin activity was the main difference observed between the protease pattern of SAS₆ and SAS₁₃F. subtilis.     

Digestive protease activity in juvenile Farfantepenaeus californiensis as a function of dissolved oxygen and temperature

Total protease, trypsin and chymotrypsin activities were examined in postlarval Farfantepenaeus californiensis (Holmes) after they had been reared for 50 days at two dissolved oxygen concentrations (5.8 and 2.6 mg L⁻¹) and three temperatures (19, 23 and 27 °C). Three replicated experiments were performed with a 12-h light/dark photoperiod. Two-way analysis of variance indicated a significant effect of temperature and oxygen (P < 0.05) on total protease and chymotrypsin activities, but no effect of oxygen was found on trypsin activity. A tendency towards increased protease, trypsin and chymotrypsin activities with acclimation temperature was observed. Total protease activity (units per mg protein) varied from 0.26 in shrimp held at 19 °C and low oxygen concentration to 1.41 in shrimp held at 23 °C and high oxygen concentration. Trypsin activity (units per mg protein) varied from 0.16 in shrimp held at 19 °C and low oxygen concentration to 0.86 in shrimp held at 27 °C and high oxygen concentration. Chymotrypsin activity (units per mg protein) varied from 0.014 in shrimp held at 19 °C and low oxygen concentration to 0.15 (units per mg protein) in shrimp held at 27 °C and low oxygen concentration. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) zymograms of hepatopancreas from each of the treatment groups showed numerous bands. The results suggest that different digestive protease enzymes arise as an adaptation mechanism to temperature and dissolved oxygen variations at this particular stage of life.     

Digestive peptidases and proteinases in the midgut gland of the pink shrimp Farfantepenaeus paulensis (Crustacea, Decapoda, Penaeidae)

Proteases from the midgut gland of the Farfantepenaeus paulensis juveniles were assessed. Enzyme activity was determined using protease substrates and inhibitors. The effect of pH, temperature and calcium on proteolytic activity was assayed. Caseinolytic activity was analysed in substrate-sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Trypsin, chymotrypsin and leucine aminopeptidase activity was detected. Proteolytic activity was strongly inhibited by the specific trypsin inhibitors. Tosyl-phenylalanine chloromethyl ketone inhibited 59.3% of chymotrypsin activity. The greatest trypsin-like activity occurred at pH 8.0 and 45 °C. Chymotrypsin-like activity reached maximal values at alkaline pH (7.2–9.0) and 55 °C. CaCl₂ did not increase trypsin-like activity, but rather inhibited it at concentrations of 30 (20%), 50 (30%) and 100 mM (50%). The substrate-SDS-PAGE zymogram revealed eight proteinase bands. Two possibly thermal-resistant (85 °C, 30 min) chymotrypsin isoforms were found, which were inhibited by phenyl-methyl-sulphonyl-fluoride. Aminopeptidase activity of enzyme extracts (Arg, Leu, Lys, Phe and Val) and the recommended concentrations of these essential amino acids in penaeid shrimp diets were positively correlated ( P <0.05). Beause protein digestion involves the combined action of different enzymes, adequate knowledge of shrimp digestion and enzyme characteristics is required for the assessment of the digestive potential of different feed sources and development of in vitro digestibility protocols.     

Seasonal changes in proteolytic enzymes of yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae) fed extruded diets containing different protein and energy levels

Seasonal variations in pepsin, trypsin and chymotrypsin activities and protein digestibility were studied in yellowtails (Seriola quinqueradiata) reared for 1 year with extruded diets containing different levels of protein. Trypsin and chymotrypsin storage levels in the digestive tissues of starved fish were affected by seasonal changes in water temperature. Actual digestion activities of trypsin and chymotrypsin were low at lower water temperatures, but pepsin activity in the stomach tissue was not affected by low temperatures. On the other hand, trypsin and chymotrypsin activities in the intestinal contents were higher during lower water temperature months, while pepsin activity in the stomach contents was low at lower water temperatures. Apparent protein digestibility (APD) did not differ among the dietary treatments in the higher water temperature months, while in colder months it was higher in fish fed diet 1 than in fish fed diets 2 and 3. The APD values reflected pepsin activity in the stomach contents in all sampling months. Therefore, lower APD in colder months seems to be attributed to lower protease activity in the gastric digesta, implying that enhanced pepsin secretion from the stomach tissue might improve protein digestibility and growth performance in yellowtails during winter.     

Protease activities, plasma free amino acids and insulin at different ages of Atlantic salmon (Salmo salar L.) with genetically different trypsin isozymes

We show significant relationships between digestion rate of dietary protein, absorption/transport rate of amino acids, and plasma insulin concentration. Digestion rate of dietary protein was indicated by protease activity ratio of trypsin to chymotrypsin in the pyloric caeca. Plasma total free amino acids and/or the ratio of essential to non-essential free amino acids indicated absorption/transport rate of amino acids. These relationships are associated with and likely to be primarily affected by genetic variation in the expression of different isozymes of trypsin, a key enzyme for feed utilization and growth, affecting digestion, absorption/transport rate of amino acids and plasma insulin levels in Atlantic salmon (Salmo salar L.).     

Ontogeny of pancreatic enzymes in larval red drum Sciaenops ocellatus

The growth, survival and trypsin, lipase and amylase activities of red drum larvae were measured in two experiments. For the first trial, a group was fed live prey only (L) and another group was fed a combination of a microparticulate diet (MPD) and live food (L-MP). For the second growth trial a group fed the MPD only (MP) and a starvation group (ST) were examined in addition to the L and L-MP treatments. Enzyme activities of live prey were measured to estimate their possible contribution to larval digestion. No significant ( P  > 0.05) differences in final size and survival were observed between treatments L and L-MP. Larvae subjected to starvation or fed the MPD diet alone were smaller than treatments fed live prey and did not survive past days 5 and 14, respectively. Trypsin, lipase and amylase activities were detectable at hatching. No significant differences ( P  > 0.05) in total enzyme activities among treatments were observed before day 14. Specific activity of trypsin, lipase and amylase peaked on day 3 (prior to first feeding) and subsequently decreased. For trypsin, the percentage of enzyme activity potentially attributable to ingested prey increased with age to a maximum of 17%. For lipase and amylase this fraction was less than 5% throughout the study, except on day 8 (12% and 24%, respectively). The lack of significant differences observed in the activity of digestive enzymes among treatments suggests that dietary regime, availability of prey and possible effects of exogenous enzymes did not significantly influence enzyme activity. Therefore, the lower growth rate observed in the L-MP, MP and starved treatments cannot be attributed to low digestive enzyme production of the enzymes measured. It is more likely that the MPD failed to supply the required nutrients for adequate development.     

Effects of dietary supplementation with feeding stimulants on yellowtail Seriola quinqueradiata (Temminck & Schlegel; Carangidae) protein digestion at low water temperatures

Feeding trials were carried out to examine substances that could be used as supplements in low‐protein/high‐lipid diets to improve protein digestion of yellowtails (Seriola quinqueradiata) during winter. Dietary supplementation with synthetic or natural (krill and squid extracts) feeding stimulants (FS) improved feed intake and growth performance of yellowtails. Moreover, the apparent protein digestibility (APD) and pepsin, trypsin and chymotrypsin secretions in fish fed diets supplemented with the different FS were superior to those in fish fed the control diet. These findings suggest that the dietary inclusion of either synthetic or natural FS is a potential tool for improving protein digestion at low water temperatures, and may provide a promising solution for the winter growth retardation experienced in yellowtail culture.     

Pigment deposition and in vitro screening of natural pigment sources for enhancing pigmentation in male Siamese fighting fish (Betta splendens Regan, 1910)

Distribution in pigment deposition was studied in male Siamese fighting fish (Betta splendens Regan, 1910) of solid Blue and solid Red phenotypes. Growths were similar, and also indicated by similar activity ratio of trypsin to chymotrypsin. Growth strategy was different at maturing stage, whereas trypsin expression decreased in solid Blue while chymotrypsin expression decreased in solid Red (P ≤ 0.05). Ranking of total pigment contents was muscle > skin > caudal fin > anal fin > dorsal fin > pelvic fin > pectoral fin. Immature fish had similar total contents and concentrations of pigments, except solid Blue had higher total contents in dorsal fin than solid Red. At maturing stage, solid Blue showed higher total pigment contents than solid Red due to higher contents in the fins. Solid blue had higher concentration in pelvic fin, while solid Red had higher in pectoral and dorsal fins. Age, phenotype and their interaction influenced pigment deposition. Determinations of pigment levels, high temperature tolerant of pigments and in vitro digestibilities of pigments, protein and carbohydrate from twenty natural sources indicated that fermented red rice was the most suitable pigment source, following with Chlorococcum sp.     

延迟首次投喂对乌江中华倒刺鲃仔鱼的补偿生长、消化酶活性及饵料日转化率的影响

为探究延迟首次投喂对乌江中华倒刺鲃(Spinibarbus sinensis)仔鱼补偿生长、消化酶活性及饵料日转化率的影响,对肠道贯通后的仔鱼进行了不同饥饿天数(H0、H1、H3、H5、H7、H9、H11)后补偿投喂17 d的实验。结果显示,全长和体重的损失率随饥饿时间的延长而增加。补偿投喂后,全长补偿率在H9组以后明显下降,体重补偿率在各实验组间无明显差异。各组全长和体重的特定生长率都呈波动性变化趋势,且实验后期各实验组都大于正常组都存在显著性差异。全长、体重及特定生长率的变化表明该饥饿仔鱼补偿投喂后能完成部分补偿生长。饥饿处理中,淀粉酶、碱性磷酸酶和胰蛋白酶随饥饿时间都呈下降趋势,脂肪酶呈先上升后下降趋势,补偿投喂后,除了淀粉酶呈先上升后下降外,其余三种酶都呈上升趋势。各组在饥饿处理下消化酶活性在实验后期与正常组存在显著差异,再投喂后与正常组差异不显著。各组在再投喂后的饵料日转化率随补偿时间呈不规则上升,但都无法恢复到正常投喂水平。综上,延迟首次投喂对中华倒刺鲃仔鱼补偿生长、消化酶活性及饵料转化都存在不同程度的影响。     

Digestive proteases of three carps Catla catla, Labeo rohita and Hypophthalmichthys molitrix: partial characterization and protein hydrolysis efficiency

Characteristics and functional efficacy of digestive proteases of Catla catla, catla, Labeo rohita, rohu and Hypophthalmichthys molitrix, silver carp were studied. Total protease activity was significantly (P < 0.05) higher in rohu (1.219 ± 0.059 U mg protein⁻¹ min⁻¹) followed by silver carp (1.084 ± 0.061 U mg  protein⁻¹ min⁻¹), and catla (0.193 ± 0.006 U mg  protein⁻¹ min⁻¹). Trypsin activity of silver carp and rohu was 89–91% higher than catla. Chymotrypsin activity was significantly (P < 0.05) higher in silver carp compared with rohu and catla. The protease activity of rohu and silver carp displayed bell‐shaped curves with maximum activity at pH 9; whereas in catla, maximum activity was found between pH 8 and 11. Inhibition of protease activity with soybean trypsin inhibitor (SBTI), phenylmethylsulfonyl fluoride (PMSF) revealed the presence of serine proteases and inhibition of activity with N‐α‐p‐tosyl‐L‐lysine‐chloromethyl ketone (TLCK) and N‐tosyl‐L‐phenylalanychloromethane (TPCK) indicated the presence of trypsin‐like and chymotrypsin‐like enzymes in all these three carps. SDS‐PAGE showed the presence of several protein bands ranging from 15.3 to 121.9 kDa in enzyme extracts of catla, rohu and silver carp. The substrate SDS‐PAGE evidenced the presence of various protease activity bands ranging from 21.6–93.7, 21.6–63.8 and 26.7–98.5 kDa for catla, rohu and silver carp respectively. In pH‐stat hydrolysis of Chilean fishmeal showed significantly (P < 0.05) higher degree of hydrolysis compared with soybean meal, silver cup (a commercial fish feed of Mexico) and wheat flour, with enzyme preparations of three fishes. The rate of hydrolysis was significantly (P < 0.05) higher in silver carp compared with others.     

Ontogenic development of digestive enzymes in bigfin reef squid (Sepioteuthis lessoniana)

Bigfin reef squid (Sepioteuthis lessoniana) is an economically important exported aquatic animal in Thailand, but little is known about its husbandry, which needs to be clarified. In this study, the ontogenic development of the main digestive enzymes (pepsin, trypsin, chymotrypsin, lipase and amylase) was investigated within 30 days after hatching (DAH). Fertilized eggs of the wild cuttlefish were hatched and then distributed into four replicate aquaria assigned to varying collection times (0, 5, 10, 15, 20, 25 and 30 DAH). The development of pepsin suggests acidic digestion functionality at 5 DAH, and its specific activity was maintained over the studied period. Specific activities of the serine proteases, trypsin and chymotrypsin, fluctuated significantly with similar pattern, and appear to be the key enzymes contributing ontogenic changes in protein catabolism. The specific activity of lipase was relatively high at 0 DAH, dramatically increased by 5 DAH, and then appeared constant until the end of observations, suggesting important role in utilizing the lipid from yolk at hatching, as well as probably in sparing protein utilization. Dramatic increase in amylase specific activity occurred by 10 DAH after which the activity was constant until 30 DAH, suggesting the utilization of carbohydrate as energy evolves comparatively late. Findings from the current study could be used to manage nutritional protocols according to the digestive enzyme patterns, as well as to develop artificial diets for rearing S. lessoniana.     

Post-prandial protease activity in the digestive tract of African catfish Clarias gariepinus larvae fed decapsulated cysts of Artemia

The alkaline proteolytic activity in the gut of African catfish larvae was studied during short time ranges from 30 min to 4 h after ingestion of decapsulated Artemia cysts. The variation in total protease and trypsin activities during the day was monitored during starvation, after one single meal ingestion, and during continuous feeding. In starved larvae the enzymatic activity was low and did not change in time. No significant endogenous secretion of digestive enzymes was detected. The level of alkaline proteolytic activity found in starved larvae was further considered as the basal level. In larvae fed only one meal during the day, the enzyme activity significantly increased from 3 h post-feeding up to a maximum level found 12 h after feeding. In the larvae receiving a meal every 4 h, the effect of feeding on the proteolytic activity was significantly different from the one in fish fed only once a day. The total protease activity in this dietary treatment changed according to the time of feeding and fluctuated around a constant level, which was intermediate between the maximum and the basal level. No rhythmic cycle of enzyme production in the fish was observed when the proteolytic activity was studied during a cycle of 24 h. When specific trypsin activity was measured, a similar pattern was found as with the total protease. The contribution of digestive enzymes from Artemia to the total digestion of food by the catfish larvae was calculated to be less than 1% of the total amount of the proteolytic activity measured in the larval gut.     

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker <Emphasis Type="Italic">Miichthys miiuy</Emphasis> larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.     

Compensatory Growth of Juvenile Flounder Paralichthys olivaceus L. and Changes in Biochemical Composition and Body Condition Indices during Starvation and after Refeeding in Winter Season

Compensatory growth and changes in biochemical composition, hematocrit and body condition indices of juvenile flounder Paralichthys olivaceus were assessed during starvation and after refeeding. Twenty juvenile fish were stocked into each 200‐L flow‐through tank to give five treatments with three replicates per treatment: control group fish (C) were hand fed to apparent satiation twice daily for 8 wk, whereas the Sl, S2, S3, and S4 fish were hand fed to apparent satiation twice daily for 7, 6, 5, and 4 wk after 1, 2, 3, and 4 wk of starvation, respectively. During starvation, weight decreased linearly with periods of feed deprivation up to 3 wk. Survival was not significantly different among treatments. At the end of the feeding trial, weight gain (g/fish) and specific growth rate (SGR) of flounder in S2 was significantly (P < 0.05) higher than those of fish in S3 or S4, but not significantly different from those of fish in C or Sl. Feed consumption of flounder (g/fish) was proportional to duration of feeding except for that of fish in S2. Feed efficiency ratio (FER) and protein efficiency ratio (PER) values for flounder in S2 were significantly (P < 0.05) higher than those for fish in C, but not significantly different from those for fish in Sl, S3, or S4. During starvation, hepatosomatic index (HSI) and lipid content of flounder without liver decreased with periods of feed deprivation. However, HSI and condition factor (CF) for flounder in S2 were significantly (P < 0.05) higher than those for fish in Sl, S3, S4 and C except for CF in Sl at the end of the feeding trial. Proximate composition of flounder without the liver was not significantly different among treatments at the end of the feeding trial. In considering above results, juvenile flounder achieved compensatory growth with up to 2‐wk feed deprivation. Compensatory growth of flounder fed for 6 wk after 2‐wk feed deprivation was well supported by improvement in SGR, FER, and PER. HSI could be a good index to monitor changes in body condition during starvation and after refeeding.