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1.
The metabolic responses of the juvenile Miichthys miiuy in terms of oxygen consumption and ammonia excretion to changes in temperature (6–25°C) and salinity (16–31 ppt) were investigated. At a constant salinity of 26 ppt, the oxygen consumption rate (OCR) of the fish increased with an increase in temperature and ranged between 133.38 and 594.96 μg O2 h−1 g−1 DW. The effect of temperature on OCR was significant (P < 0.01). Q10 coefficients were 6.80, 1.41, 1.29 and 2.36 at temperatures of 6–10, 10–15, 15–20 and 20–25°C, respectively, suggesting that the juveniles of M. miiuy will be well adapted to the field temperature in the summer, but not in the winter. The ammonium excretion rates (AER) of the fish were also affected significantly by temperature (P < 0.01). The O:N ratio at temperatures of 6, 10, 15 and 20°C ranged from 13.12 to 20.91, which was indicative of a protein-dominated metabolism, whereas the O:N at a temperature of 25°C was 51.37, suggesting that protein-lipids were used as an energy substrate. At a constant temperature of 15°C, the OCRs of the fish ranged between 334.14 (at 31 ppt) and 409.68 (at 16 ppt) μg O2 h−1 g−1 DW. No significant differences were observed in the OCR and AER of the juveniles between salinities of 26 and 31 ppt (P > 0.05). The OCR and AER at 16 ppt were, however, significantly higher than those at 26 and 31 ppt (P < 0.05), indicating salinity lower than 16 ppt is presumably stressful to M. miiuy juveniles.  相似文献   

2.
Retentions of total n-3 and n-6 essential fatty acids (EFAs) were assessed in Atlantic salmon (Salmo salar L.) parr held at 8 °C and 2 °C until they increased in weight from ca. 19 g to 38 g. Feeds contained sandeel oil or a rapeseed:linseed oil blend at 21 and 34% dietary fat. EFA retention efficiencies [(g EFA gained g EFA ingested-1) × 100] were estimated by the 'mass balance method' from measurements of feed intake, changes in biomass for each tank of fish, and fatty acid compositions of the feeds and fish. The n-3 EFA retentions were higher (overall mean 71%) across feed treatments and temperatures than the n-6 EFA retentions (overall mean 63%). Retentions of the n-3 fatty acids were higher in the fish given the feeds with the lower fat content (77% vs. 65%), implying improved retention with reduced n-3 EFA availability. n-3 EFA retention tended to be higher at 2 °C than at 8 °C, although this was not consistent across feeds. At low temperature there was very high retention of the n-3 EFAs in feeds containing sandeel oil (80%). Such high retention may represent an adaptation response to low temperature. Lower n-6 EFA retentions imply that more n-6 fatty acids were metabolized than n-3 EFAs. Feed oil influenced retention of the n-6 fatty acids, retention being lower for the salmon parr given the feeds containing sandeel oil (56% vs. 71%). This could indicate a higher tissue deposition of n-6 fatty acids when they are freely available via the diet. Abbreviations: AA – arachidonic acid (C20:4 n-6); DHA – docosahexaenoic acid (C22:6 n-3); EFA – essential fatty acid; EPA – eicosapentaenoic acid (C20:5 n-3); HUFA – highly-unsaturated fatty acid (\ge4 double bonds); MUFA – monounsaturated fatty acid (1 double bond); PL – phospholipid; PUFA – poly-unsaturated fatty acids (\ge2 double bonds); SFA – saturated fatty acid (no double bond); TAG – triacylglycerol. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
Three case studies of ammonia autointoxication of the common carp (Cyprinus carpio L.) are described. In the first case, carp yearlings with a full digestive tract were transferred during the growing period from pond water (22°C) to tap water (17°C). In the second case, marketable carp were transferred from the fishing ground of a pond (18°C) to a storage pond (10–12°C). Harvest was performed in late September when the fish were still ingesting natural feed. In the third case, marketable carp after storage for 1 month were transferred to storage ponds with markedly lower water temperature. Stress because of harvest and handling also occurred in this case. In all cases, highly increased concentrations of ammonia were found in the blood plasma of the fish (mean ± SD 1760 ± 350 μmol L−1 in the first case, 870 ± 540 μmol L−1 in the second case, and 880 ± 150 μmol L−1 in the third case). Highly congested, dark-red coloured, oedematous gills were observed for all specimens. We can avoid similar cases of ammonia autointoxication by protection of fish from sudden changes of temperature during rearing, harvesting, and handling.  相似文献   

4.
To investigate the effect of water temperature on gamete maturation and gamete quality, European grayling (Thymalus thymallus) were held under different temperature regimes prior to spawning. Maturation of males and females and their gamete quality depended strongly on temperature regime. The highest percentages of maturing fish and highest gamete quality were obtained under a creek water temperature regime with natural seasonal fluctuations. In warmed creek water (3–4°C), at a constant temperature of 8–9°C, and under an abruptly increasing temperature, regime maturation rates and gamete quality were reduced. The effect was more pronounced in females than in males. The spawning dates of different wild Austrian grayling populations were also correlated with water temperature data collected during the last 10–15 years. The mean spawning date expressed as the number of days from 21 December until spawning ranged from 98 to 111 days for lower elevation populations, while it was considerably delayed for an alpine population. All populations spawned at water temperatures of 5.5–7.2°C. Regression analysis indicated that spawning date correlated with (1) the overall mean water temperature from 21 December until spawning, (2) the mean water temperature during both the last 10 days and 15 days before spawning, and (3) the difference between mean January temperature and that of the last 15 days before spawning. The regression functions indicate that an increase in water temperature from 21 December to spawning of 1°C advances spawning by 5? days, and an increase of 1°C in the last 10–15 days advances spawning by 3? days.  相似文献   

5.
Gamma-aminobutyric acid (GABA) at 50 μg/ml and porcine growth hormone (GH) at 0.025 IU/ml were tested to see whether these chemicals would reduce the stress experienced by euryhaline rotifers Brachionus plicatilis species complex (L-, S- and SS-morphotypes) during low temperature (4–12°C) storage. Rotifers cultured at 25°C were transferred to 4–12°C for 10–30 days and transferred back to 25°C for recovery. GABA or GH were added to the rotifers at three different time points: 6 h before transfer from 25°C to low temperature (6h−), on day 7 after preservation at low temperature (7d+) and on the first day of recovery. For L-type rotifers, the GH treatment before the transfer to 4°C for 30 days was effective for better survival, while the GABA treatment was most effective for the S-type preserved at 10°C for 14 days. For the SS-type, the chemical treatments were not effective when the rotifers were preserved at 12°C for 14 days. After low temperature preservation, GABA treatments with the S- and SS-type rotifers just after their transfer to 25°C induced a relatively faster recovery of the rotifer population.  相似文献   

6.
In this study we examined the endocrine mediation between environmental factors (temperature and photoperiod) and the brain–pituitary–gonadal axis in females of pejerrey Odontesthes bonariensis. Changes in the expression of brain gonadotropin-releasing hormones (GnRHs) and gonadotropin (GtH) subunit [follicle stimulating-β (FSH-β), luteinizing hormone-β (LH-β), glycoprotein hormone-α (GPH-α)] genes, plasma gonadal steroids [estradiol (E2) and testosterone (T)], gonadal histology, and gonadosomatic index (GSI) in adult females exposed to combinations of short-day (8 h) or long-day (16 h) photoperiods and low (12°C) or high (20°C) temperatures after winter conditions (8 h light, 12°C) were analyzed. Pejerrey females kept under the short photoperiod had low GSIs, and their ovaries contained only previtellogenic oocytes regardless of the experimental temperature. In contrast, females exposed to the long photoperiod had high GSIs and ovaries with vitellogenic oocytes at both temperatures. These fish also showed a significantly higher expression of sGnRH, pjGnRH, cGnRH-II (the three different GnRH variants found to date in the pejerrey brain), FSH-β, LH-β and GPH-α genes and plasma E2 levels than those at the shorter photoperiod. No significant changes were observed in plasma T levels. Based on these results, we concluded that the increase in day length but not that of temperature triggers the maturation of pejerrey females after the winter period of gonadal rest and that this occurs by an integrated stimulation of the various components of the brain–pituitary–gonad axis.  相似文献   

7.
The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut Hippoglossus hippoglossus and in 114 (50 females and 64 males) individually tagged turbot Scophthalmus maximus. The halibut were reared at 11 °C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. The turbot were reared at 16 °C on three different light regimes: constant light (LD24:0), 16 h light:8 h darkness (LD16:8), or simulated natural photoperiod (LDN). After 6 months on the different photoperiods, the turbot was reared together on LDN for approximately 12 months until first maturation. Juveniles subjected to continuous light (halibut) or extended photoperiods (halibut and turbot) exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, when the photoperiod increased naturally with day-length or when fish were abruptly switched from being reared on short-day conditions to continuous light, a subsequent increase in growth rate was observed. This growth enhancing effect of extended photoperiods was more apparent on a short time scale in Atlantic halibut than in turbot, but both species show significant long-term effects of extended photoperiods in the form of enhanced growth. In both species lower maturation of males was seen in groups exposed to extended or continuous light compared to LDN and this could be used to reduce precocious maturation in males leading to overall increase in somatic growth. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

8.
The growth of age-1 Pacific saury Cololabis saira was compared based on an analysis of the body-length frequency distributions, radius of the annual ring (otolith hyaline zones; ROH), and growth patterns in otolith increments. Fish were sampled at various locations between off the Japanese coast (144°E) and in the Central Pacific (160°W) in June and July 2006, and the measurements were compared among the stations ranging over six longitudinal areas, each with a longitudinal area of 10°. The mode of body-length frequency distributions of age-1 fish was larger in fish sampled west of 160°E (size class modes of 32.0–32.5 and 31.5–32.0 cm, respectively, in each 10° longitude area) than in those sampled east of 170°E (28.5–29.0 or 29.0–29.5 cm in 3 areas). The ROH was also larger in the former group (west of 160°E) than in the latter group (east of 170°E), but hatch periods of these two groups and age in days when the hyaline zones form in August or September did not differ based on the analysis of otolith growth increments. The growth difference occurred in the period between when the fish started their northward migration and when the hyaline zone was formed. These results indicate that the habitats of the two groups were separate until at least June or July of their second year of life.  相似文献   

9.
“Burnt meat” is a term used to describe the white (pale, grainy, exudative) muscle of yellowtail or tuna. It (with lightness parameter, L* ≥ 55) was observed after 2 h storage in the suffocate in air (SA) 29°C group and after 4 h storage in the spinal cord destruction (SCD) 29°C group. In the SA 17°C group, burnt meat was also observed after 4 h storage. In contrast, the meat in the SCD 17°C group was normal until after 12 h storage. The myosin heavy chain (MHC) was more degraded than the other myofibrillar proteins, and some protein bands increased in the burnt meat. The protease that leads to the degradation of MHC was investigated using myofibrils from the meat. EDTA completely suppressed the degradation, indicating that a myofibril-bound EDTA-sensitive protease (MBESP) may exist in yellowtail muscle and this caused the degradation of MHC. The optimum pH and temperature of MBESP in yellowtail were 5.0 and 50–60°C, respectively.  相似文献   

10.
The effect of thermal history (16 and 20°C) on growth of juvenile turbot, Scophthalmus maximus (initial mean weight 72.6 g, n = 157) was studied. Fish were divided into four groups, two groups remaining at constant temperature (C16, C20), while fish in the other groups were transferred from either 16 to 20°C (F16-20) or from 20 to 16°C (F20-16). Between 35 and 42 fish in each tank were individually tagged at the start of the experiment. The final mean weights were significantly higher in the F20-16 group (230 g) than in the C20 (213 g), F16-20 (211 g) and C16 (205 g) groups. The overall growth rate was highest in the F20-16 group (1.17% day−1) but comparable in the three other groups (1.00–1.04% day−1). Our findings indicate that, even at near-optimal temperature for a given size, the temperature history of the fish may influence future growth. Based on these indications, we conclude that as turbot grow larger, the temperature should be reduced to take advantage of the change in optimal temperature for growth with increasing fish size rather than rearing at constant temperatures.  相似文献   

11.
Photosynthetic activity of Zostera japonica seedlings was measured using a gas volumeter at 0 and 6 days in culture under eight light (0–800 μmol photons/m2/s) and ten water temperature conditions (5–35°C). Seedlings from Ago Bay, Mie Prefecture were cultured in incubators accurately controlled at each test temperature for 1 week. After 1 week, maximum gross photosynthesis (P maxg) appeared at 29°C and most seedlings cultured at 30–35°C bleached and withered. At the same time, the light compensation point (I c) increased only at 30°C during the culture period. As a result, the upper critical water temperature for survival was 29°C in Z. japonica seedlings, which agrees well with that for the southern boundary of Z. japonica around Japanese coast. It is necessary to monitor this species around this boundary as a bio-indicator for seawater warming.  相似文献   

12.
This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two temperatures (20 or 26°C), on a commercial diet (21.4 g DP mJ DE−1) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency (ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26°C respectively. ERE demonstrated a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26°C respectively. Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and temperature. The partial utilization efficiencies of DE for protein (k p) and lipid (k l) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements estimated using linear regression were independent of temperature for DP (0.47 g DP kg−0.7 day−1) while maintenance requirements for DE increased with increasing temperature (44.2–49.6 kJ DE kg−0.8 day−1). Relative feed intake was greatest for small mulloway fed to satiation at 26°C and this corresponded to a greater increase in growth. Large mulloway fed to satiation ate significantly more at 26°C, but did not perform better than the corresponding satiated group held at 20°C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE−1.  相似文献   

13.
The amelioration effect of high dietary protein against stress was evaluated in Labeo rohita fingerlings, exposed to heat shock. Two hundred and forty fingerlings (6.57 ± 0.04 g, average weight ± SE) were randomly distributed into 4 treatment groups, each with 4 replicates was fed with either of four diets containing different levels of protein (20, 30, 40 or 45%). Water temperatures of all the treatments were within the range of 25.5–26.5°C throughout the experimental period of 30 days. After 30 days of feeding, fish were given heat shock by exposing to 38°C for 2 h. Heat shock significantly decreased (P < 0.05) liver glycogen content in treatment groups fed with 20 and 30% dietary protein, whereas unaffected in the 40 and 45% protein-fed groups. Heat shock significantly increased (P < 0.05) serum glucose and cortisol level in all the treatments. The 40 and 45% dietary protein–fed groups registered significantly higher survival (%) after the heat shock compared with their lower-protein counterparts. Heat shock increased the glycolytic, gluconeogenic, protein metabolic and antioxidative enzymes to cope up with thermal stress. Our results indicate that high-protein diet (≥40%) combats the stress due to heat shock in Labeo rohita.  相似文献   

14.
An 8-week feeding trial was conducted in a flow-through system (1–1.5 L min−1) at 27°C to determine dietary protein requirement for Channa punctatus fingerlings (4.58 ± 0.29 g) by feeding six isocaloric diets (18.39 kJ g−1, gross energy). Diets containing graded levels of protein (300, 350, 400, 450, 500 and 550 g kg−1) were fed to triplicate groups of fish to apparent satiation at 09:00 and 16:00 h. Maximum absolute weight gain (AWG; 8.11 g fish−1), specific growth rate (SGR; 1.82%) and best feed conversion ratio (FCR; 1.48) were recorded in fish fed diet containing 450 g kg−1 protein, whereas protein efficiency ratio (PER; 1.52), protein retention efficiency (PRE; 25%), energy retention efficiency (ERE; 78%) and RNA/DNA ratio (3.01) were maximum for the group fed dietary protein at 400 g kg−1. Second-degree polynomial regression analysis of AWG, SGR and FCR data against varying levels of dietary protein yielded optimum dietary protein requirement of fingerling between 462.24 and 476.72 g kg−1, whereas the regression analysis of PER, PRE, ERE and RNA/DNA ratio data showed a lower protein requirement of 438.28–444.43 g kg−1 of the diet. Considering the PER, PRE, ERE and RNA/DNA ratio as more reliable indicators, this protein requirement is recommended for developing quality protein commercial feeds for C. punctatus fingerlings.  相似文献   

15.
Fluctuations in water temperature can have important physiological consequences for fishes. Effects of daily thermal cycles are well studied and can be beneficial, increasing prey consumption and growth rates when mean and maximum temperatures of the fluctuations are at or below the species’ optimum temperature. While less studied, subdaily temperature fluctuations are also common in many aquatic habitats and can be caused by both natural and anthropogenic processes. We performed laboratory experiments to examine how two fish species (yellow perch, Perca flavescens, and walleye, Sander vitreus) with similar thermal preferences respond to chronic exposure to subdaily temperature variability. We selected temperature treatments that reflected observed thermal variation after examining water temperature data from multiple aquatic systems. We then separately exposed yellow perch and walleye to a stable 23 °C treatment and 12‐h cycles of 23 ± 2 °C or 23 ± 4 °C for 45 days. Adult yellow perch exposed to fluctuations of 23 ± 4 °C over 12 h expressed higher consumption, growth and food conversion efficiency than fish experiencing stable 23 °C. Temperature fluctuations, though, resulted in mortalities and the development of skin ulcers in yellow perch that did not occur under stable temperatures. In contrast, the same 12‐h temperature fluctuations did not result in mortalities or stress responses in juvenile walleye. Moreover, unlike yellow perch, growth rates of walleye were lower under 12‐h temperature fluctuations compared with the stable 23 °C treatment. Our results indicate that species with similar thermal preferences can respond differently to the same subdaily temperature fluctuations.  相似文献   

16.
Three trypsin isoforms A, B and C were purified to homogeneity from the viscera of sardinelle (Sardinella aurita). Purification was achieved by ammonium sulfate precipitation (20–70% (w/v)), Sephadex G-100 gel filtration and Mono Q-Sepharose anion-exchange chromatography. The molecular weights of these purified enzymes were estimated to be 28.8 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). Based on the native PAGE and casein-zymography, each purified trypsin appeared as a single band. Trypsins A and C exhibited the maximal activity at 55°C, while trypsin B at 50°C. All isoforms showed the same optimal pH (pH 9.0) using Nα-benzoyl-dl-arginine-p-nitroanilide (BAPNA) as a substrate. The three trypsins were stable at temperatures below 40°C and over a broad pH range (7.0–11.0). The activities of the three isoforms were strongly inhibited by soybean trypsin inhibitor and phenylmethylsulfonyl fluoride, a serine protease inhibitor, and partially inhibited by ethylenediaminetetraacetic acid, a metalloenzyme inhibitor. Kinetic constants of trypsins A, B and C for BAPNA were evaluated at 25°C and pH 9.0. The values of K m and k cat were 0.125, 0.083 and 0.10 mM, and 2.24, 1.21 and 5.76 s−1, respectively. The N-terminal sequences of the first 10 amino acids were “I V G G Y E C Q K Y” for trypsin A and “I V G G Y E A Q S Y” for trypsins B and C. These sequences showed highly homology to other fish trypsins.  相似文献   

17.
The present paper describes the growth properties of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C, and a group reared under “temperature steps” i.e. with temperature reduced successively from 16 to 13 and 10 °C. Growth rate and feed conversion efficiency of juvenile Atlantic cod were significantly influenced by the interaction of temperature and fish size. Overall growth was highest in the 13 °C and the T-step groups but for different reasons, as the fish at 13 °C had 10% higher overall feeding intake compared to the T-step group, whereas the T-step had 8% higher feeding efficiency. After termination of the laboratory study the fish were reared in sea pens at ambient conditions for 17 months. The groups performed differently when reared at ambient conditions in the sea as the T-step group was 11.6, 11.5, 5.3 and 7.5% larger than 7, 10, 13 and 16 °C, respectively in June 2005. Optimal temperature for growth and feed conversion efficiency decreased with size, indicating an ontogenetic reduction in optimum temperature for growth with increasing size. The results suggest an optimum temperature for growth of juvenile Atlantic cod in the size range 5–50 g dropping from 14.7 °C for 5–10 g juvenile to 12.4 °C for 40–50 g juvenile. Moreover, a broader parabolic regression curve between growth, feed conversion efficiency and temperature as size increases, indicate increased temperature tolerance with size. The study confirms that juvenile cod exhibits ontogenetic variation in temperature optimum, which might partly explain different spatial distribution of juvenile and adult cod in ocean waters. Our study also indicates a physiological mechanism that might be linked to cod migrations as cod may maximize their feeding efficiency by active thermoregulation.  相似文献   

18.
Climate change is predicted to increase the average water temperature and alter the ecology and physiology of several organisms including fish species. To examine the effects of increased water temperature on freshwater fish reproduction, adult European bullhead Cottus gobio of both genders were maintained under three temperature regimes (T1: 6–10, T2: 10–14 and T3: 14–18°C) and assessed for gonad development (gonadosomatic index—GSI and gonad histology), sex steroids (testosterone—T, 17β-estradiol—E2 and 11-ketotestosterone—11-KT) and vitellogenin (alkali-labile phosphoprotein phosphorus—ALP) dynamics in December, January, February and March. The results indicate that a 8°C rise in water temperature (T3) deeply disrupted the gonadal maturation in both genders. This observation was associated with the absence of GSI peak from January to March, and low levels of plasma sex steroids compared with T1-exposed fish. Nevertheless, exposure to an increasing temperature of 4°C (T2) appeared to accelerate oogenesis with an early peak value in GSI and level of plasma T recorded in January relative to T1-exposed females. In males, the low GSI, reduced level of plasma 11-KT and the absence of GSI increase from January to March support the deleterious effects of increasing water temperature on spermatogenesis. The findings of the present study suggest that exposure to elevated temperatures within the context of climate warming might affect the reproductive success of C. gobio. Specifically, a 4°C rise in water temperature affects gametogenesis by advancing the spawning, and a complete reproductive failure is observed at an elevated temperature of 8°C.  相似文献   

19.
The interaction of methyl-parathion with the albumin of Piaractus mesopotamicus (Holmberg 1887) (= pacu), a fish species typical of Brazilian rivers, was studied and the results compared with known values for human and bovine albumin obtained in an earlier investigation. Methyl-parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) is an organophosphorous pesticide still used in agriculture and fish farming in many countries. The fluorescence quenching technique with tryptophan as a natural probe was used to detect for the presence of methyl-parathion. Fluorescence can be mathematically expressed by the Stern–Volmer equation to calculate quenching constants, and changes in the behavior of Stern–Volmer curves at different temperatures indicate the nature of the mechanism causing the quenching. Our results indicate that methyl-parathion forms a complex with fish albumin. The estimated association constant is 9.73 × 103 (± 4.9 × 102) M−1 at 25°C.  相似文献   

20.
Three pepsinogens (PG1, PG2, and PG3) were highly purified from the stomach of freshwater fish rice field eel (Monopterus albus Zuiew) by ammonium sulfate fractionation and chromatographies on DEAE-Sephacel, Sephacryl S-200 HR. The molecular masses of the three purified PGs were all estimated as 36 kDa using SDS–PAGE. Two-dimensional gel electrophoresis (2D-PAGE) showed that pI values of the three PGs were 5.1, 4.8, and 4.6, respectively. All the PGs converted into corresponding pepsins quickly at pH 2.0, and their activities could be specifically inhibited by aspartic proteinase inhibitor pepstatin A. Optimum pH and temperature of the enzymes for hydrolyzing hemoglobin were 3.0–3.5 and 40–45°C. The K m values of them were 1.2 × 10−4 M, 8.7 × 10−5 M, and 6.9 × 10−5 M, respectively. The turnover numbers (k cat) of them were 23.2, 24.0, and 42.6 s−1. Purified pepsins were effective in the degradation of fish muscular proteins, suggesting their digestive functions physiologically.  相似文献   

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