Juvenile Soft-shelled Turtles Research Articles

Bacillus cereus causes fatal disease in soft-shelled turtle (Trionyx sinensis)

Soft-shelled turtle (Trionyx sinensis) is one of the most important aquacultural species in China. In recent years, an infectious disease frequently occurred in soft-shelled turtle, which exhibited similar symptoms, including craned necks, ulcerated pores on shells, hemorrhagic intestinal mucosa and heart, intumescent liver and spleen. In this study, a Gram-positive rod bacterial strain BC12 with vigorous hemolytic and lipolytic activity isolated from the sick soft-shelled turtles. Strain BC12 was identified as Bacillus cereus via 16S rRNA phylogenetic analysis and species-specific gene amplification. The juvenile soft-shelled turtles challenged with B. cereus BC12 exhibited similar symptoms as those natural infections, and the 50% lethal dose (LD50) is 3.89 × 105 colony-forming unit (CFU). Pure B. cereus re-isolated from the heart and liver of turtles infected with BC12. Noticeable pathological changes, including necrosis in the heart and liver and damage in the germinal center of the spleen, were observed in the B. cereus BC12 infected turtles for the first time. Antibiotics susceptibility assay showed that B. cereus BC12 is sensitive to the aminoglycosides, polypeptides, most of the cephalosporins and quinolones, which might be chosen as candidates to prevent and treat B. cereus infection.

Antioxidant defense response during hibernation and arousal in Chinese soft-shelled turtle Pelodiscus sinensis juveniles

Antioxidant defense is essential for animals to cope with homeostasis disruption during hibernation. The present study aimed to investigate the antioxidant defense response of juvenile soft-shelled turtle Pelodiscus sinensis during hibernation and following arousal. Turtle brain, liver, and kidney samples were collected at pre-hibernation (17 °C mud temperature; MT), during hibernation (5.8 °C MT) and after arousal (20.1 °C MT) in the field. Transcript levels of NF-E2-related factor 2 (Nrf2) decreased significantly during hibernation and recovered after arousal in all tissues. Cerebral and nephric copper-zinc superoxide dismutase (Cu/Zn SOD), catalase (CAT), glutathione peroxidase 3 (GPx3) and nephric GPx4 mRNA showed similar changing patterns as Nrf2. Cerebral Mn SOD, GPx1 and nephric GPx1 up-regulated after arousal. Hepatic Cu/Zn SOD, GPx1 and GPx3 mRNA kept stable, except hepatic GPx4 increased during hibernation. Hepatic Mn SOD and CAT increased after arousal. In the GSH system, mRNA levels of glutathione synthetases (GSs) kept stable during hibernation and up-regulated after arousal in most tissues except nephric GS2 mRNA remained unchanged. Gene expressions of glutathione reductase (GR) exhibited a tissue specific changing pattern, while those of glutathione-S-Transferase (GST) shared a similar pattern among tissues: remained stable or down-regulated during hibernation then recovered in arousal. In contrast to these diverse responses in gene expressions, most of the antioxidant enzyme activities maintained high and stable. Overall, no preparation for oxidative stress (POS) strategy was found in enzymatic antioxidant system in P. sinensis juveniles during hibernation, the Chinese soft-shelled turtles were able to stay safe from potential oxidative stress during hibernation by maintaining high level activities/concentrations of the antioxidant enzymes/antioxidants.

Effects of Sunlamp-Based Lighting Mode on Growth Performance, Survival Rate, Stress Response, and Oxidative Stress of Juvenile Chinese Soft-Shelled Turtles (Pelodiscus sinensis)in a Greenhouse

HighlightsSunlamps with UV and visible light were used in large-scale farming of Chinese soft-shelled turtles in a greenhouse.The effects of lighting mode on the growth performance, survival rate, stress response, and oxidative stress of juvenile Chinese soft-shelled turtles were studied.Lighting mode had significant impacts on survival rate, stress, and oxidative stress of Chinese soft-shelled turtles.Lighting the basking area only was the optimal lighting mode and caused less stress for Chinese soft-shelled turtles.Abstract. To investigate the effects of sunlamp-based lighting mode on the growth performance, survival rate, stress response, and oxidative stress of juvenile soft-shelled turtles in a greenhouse, four lighting modes with three replicates were used in this study: lighting the basking area and water simultaneously (LBW), lighting the water only (LW), lighting the basking area only (LB), and no light (NL). Results showed that the final weight, weight gain rate, and specific growth rate had no significant differences among treatments. The survival rate was significantly lower in LBW than in NL, while no significant differences were observed among NL, LB, and LW. On the physiological level, serum cortisol level was significantly lower in LB compared to the other two treatments with light, and glucose level was significantly lower in LB than in LW and NL. With regard to oxidative stress, indexes indicated that the turtles suffered less oxidative stress in LB. Glutathione peroxidase (GSH-PX) was significantly lower in LB compared to the other three treatments. Total antioxidant capacity (T-AOC) was significantly lower in LB, as well as in LW and NL, than in LBW, and no significant differences were found among LB, LW, and NL. Additionally, complement 3 (C3) was significantly higher in LB than in NL, which indicated that the turtles had higher immune-related protein in LB. On the whole, the results demonstrated that lighting mode had significant impacts on survival rate, stress response, and oxidative stress. It can be concluded that lighting the basking area only is the optimal lighting mode for soft-shelled turtles in a greenhouse. From the perspective of breeding welfare, soft-shelled turtles are suggested to be provided with a separate area for basking when cultured in a greenhouse. Keywords: Chinese soft-shelled turtle, Lighting mode, Oxidative stress, Stress response, Survival rate.

Effects of Photoperiod on Growth, Digestive Enzyme Activity, Stress, and Oxidative Status of Juvenile Chinese Soft-Shelled Turtles (Pelodiscus sinensis) in a Greenhouse

HIGHLIGHTSArtificial sunlight with the main components of UVB, UVA, and visible light was used to investigate the influence of photoperiod on large-scale farming of juvenile Chinese soft-shelled turtles in a greenhouse.The effects of photoperiod on digestive enzyme activity, stress, and oxidative status of juvenile Chinese soft-shelled turtles were revealed.The optimal photoperiod for juvenile Chinese soft-shelled turtles reared in a greenhouse was 0 h light:24 h dark.Abstract. To improve light conditions for soft-shelled turtles in a greenhouse, the effects of photoperiod on growth, digestive enzyme activity, stress, and oxidative status of juvenile Chinese soft-shelled turtles were investigated. In this study, juvenile Chinese soft-shelled turtles were reared under three photoperiods (hours light:hours dark), i.e., 0L:24D, 6L:18D, and 12L:12D) for four months. Results demonstrated that differences in growth were insignificant during the experiment, but the growth parameters of final weight, weight gain rate (WGR), and feed conversation ratio (FCR) were better at 0L:24D, and the survival rate was significantly higher at 0L:24D than at 12L:12D. Regarding digestive function, serum trypsin activity was significantly higher at 0L:24D than at 6L:18D, while lipase activity was significantly higher at 0L:24D than at 12L:12D. For the stress response parameters, serum cortisol level was significantly lower in turtles exposed to 0L:24D compared to the other treatments. With regard to antioxidant enzyme activities, the total antioxidant capacity (T-AOC) was significantly lower at 0L:24D compared to the other treatments, while superoxide dismutase (SOD) activity was significantly higher in turtles exposed to 0L:24D. The activity of glutathione peroxidase (GSH-PX) was significantly lower at 0L:24D than at 12L:12D. The malonaldehyde (MDA) activity was a little lower at 0L:24D than at 6L:18D; however, it significantly decreased in turtles exposed to 12L:12D. On the whole, the results indicated that the photoperiod treatments had no significant effects on the growth of juvenile Chinese soft-shelled turtles, while extended light exposure may cause physiological stress in turtles. Considering the survival rate, digestive function, cortisol level, and oxidative status, it is suggested that juvenile soft-shelled turtles should be reared under a 0L:24D photoperiod. Keywords: Chinese soft-shelled turtle, Digestive enzyme activity, Growth, Oxidative status, Photoperiod, Stress.

Thiamine requirement of Chinese soft‐shelled turtle,Pelodiscus sinensis(Wiegmann)

The objective of the present study was to estimate the dietary thiamine (vitamin B1) requirement of juvenile soft-shelled turtles, Pelodiscus sinensis. Eight experimental diets containing 0, 1.90, 3.63, 5.65, 7.51, 9.62, 11.37 and 13.64 mg thiamine/kg diet were fed to 160 soft-shelled turtles reared individually for 10 weeks. The turtles had an average weight of 5.33 ± 0.21 g. Among all the dietary groups, weight gain, feed utilization and tissue thiamine were the lowest in the turtles fed with a thiamine-free diet. The variables increased when dietary thiamine increased and then levelled off beyond 3.63 mg/kg diet. In contrast, plasma pyruvate and lactate concentrations in turtles decreased when dietary thiamine increased and then levelled off beyond 3.63 and 5.65 mg/kg diet respectively. Estimation using a broken-line regression model, the vitamin B1 requirement of soft-shelled turtles was 3.2 mg thiamine/kg diet based on weight gain and plasma lactate concentration. When tissue thiamine and plasma pyruvate concentrations were used as the indicators, the estimated requirement was 5.4–6.5 mg/kg diet.

Physiological responses in vitamin C system during hibernation in juvenile Chinese soft-shelled turtle Pelodiscus sinensis

Vitamin C (Vc) is an important antioxidant that helps turtles tolerating stressful environment. This work quantified changes in tissue Vc levels during winter hibernation in the soft-shelled turtle Pelodiscus sinensis, to reveal the stress response pattern of tissue Vc during hibernation and contribute basic data for turtle culture. We sampled juvenile soft-shelled turtles at pre-hibernation (17.0°C mud temperature; MT), during hibernation (5.8°C MT) and after arousal (20.1°C MT) in the field. The transcript levels of the gene encoding L-gulonolactone oxidase (GLO), the key enzyme for Vc synthesis, decreased significantly during hibernation. However, GLO activity did not match the GLO transcription patterns and remained stable during hibernation, and showed temperature-dependent kinetic characteristics. Vitamin C levels in the brain, liver, kidney, and spleen (but not muscle) all decreased significantly during hibernation, but recovered to pre-hibernation levels or even higher levels after arousal. The soft-shelled turtle endured 5 months of hibernation with no significant oxidative damage in most tissues, except in the spleen. Splenic Vc was nearly exhausted during hibernation, accompanied by a significantly elevated malonaldehyde (MDA) level. Although the high level of oxidative damage quickly decreased after arousal, the potential tissue damage in the spleen during hibernation might account for the weakened immune capacity of turtles after hibernation.

Impact of Dietary Cornstarch Levels on Growth Performance, Body Composition and Digestive Enzyme Activities of Juvenile Soft-Shelled Turtle (Pelodiscus sinensis)

Abstract We conducted an 8-week feeding trial to determine the effects of dietary starch levels on growth performance, body composition, and digestive enzyme activities of juvenile soft-shelled turtles. Six fish meal-based diets containing 120, 180, 240, 300, 360 and 420 g kg−1 cornstarch were formulated. Body weight gain (BWG), crude protein concentration in whole body, as well as protease activity increased with increasing dietary starch levels until the highest at 240–300 g kg−1, but it was decreased at higher dietary starch content. In contrast, the feed conversion ratio, moisture content and hepatosomatic index were the lowest at 240–300 g kg−1 of cornstarch. The weight gain correlated significantly with the survival rate, the crude protein composition and the protease activity, but correlated negatively to the moisture content and the hepatosomatic index. The optimal dietary starch levels for the maximum BWG and maximum protease activity were 267.25 g kg−1 and 266.79 g kg−1, respectively. The α-amylase activity was the lowest at 120 g · kg−1 of cornstarch, and increased with increasing cornstrach content. The lipase activity and the amount of crude lipid in the turtles were not influenced by dietary cornstarch. Our results suggest that around 300 g kg−1 of cornstarch in diets is optimal for juvenile soft-shelled turtles.

Digital Gene Expression Profiling reveals transcriptional responses to acute cold stress in Chinese soft-shelled turtle Pelodiscus sinensis juveniles

Turtles are well known for their stress tolerance, including an ability to deal with temperature extremes or rapid thermal change. To know more about the comprehensive molecular basis of thermal stress responses in turtles, we assessed differentially expressed genes (DEGs) in the brain, liver and kidney of juvenile soft-shelled turtles, Pelodiscus sinensis, after acute cold stress (28 °C–8 °C acute transfer and held for 12 h) and following recovery (back to 28 °C and held for 24 h) by digital gene expression profiling. Selected DEGs were also validated via real-time PCR. We found the fewest DEGs in the brain, only one-tenth of the number seen in liver, indicating a tissue-specific gene expression pattern. The DEGs indicated the potential activation of several important functions in response to cold stress and recovery in P. sinensis. This included response to oxidative stress or regulation of reactive oxygen species metabolism in the brain and liver, cerebral inositol metabolism, hepatic monosaccharide metabolism, hepatic complement system, renal DNA repair mechanisms, and TNF and PI3K-Akt signaling pathways in the kidney. These functions likely responded to cold stress in different tissues of P. sinensis to help minimize or repair cell damage as well as enhance innate immunity. The outcomes of this study provide some fundamental insight into the tissue specific complex mechanisms underlining cold stress responses in the soft-shelled turtle P. sinensis.

Modern greenhouse culture of juvenile soft-shelled turtle, Pelodiscus sinensis

Chinese soft-shelled turtle (Pelodiscus sinensis) is a favorite food for the Asian because of its high nutritional and medicinal value. Based on an estimate production of 350,000 MT in 2015, soft-shelled turtle culture industry in China values US$5.22 billion. In central China, overwinter in greenhouse is necessary for the juvenile turtle. The use of coal boiler to heat up the water to 30 °C is a common practice, however, brings in air pollution and CO2 emission too. A modern greenhouse equipped with ground source heat pump was built in 2010 and operated during 2014–2015 for 10 months to culture juvenile turtle. Besides heating system, the other innovative features such as skirt-shaped 3-D shelter, underwater feeding platform wok-shaped tank bottom with central drainage, and semi-homemade soft shell-shaped pellet together achieved excellent rearing performance, such as high turtle productivity of 23.7 kg m−2, high survival 86%, low feed efficiency-feed conversion rate 1.26 and good water quality-dissolved oxygen >5 mg L−1, and nitrite and ammonia concentration all time within safe range. Moreover, it is a lucrative business which brought in an estimated net profit of 76%.

Effects of dietary vitamin C on growth, lipid oxidation, and carapace strength of soft-shelled turtle, Pelodiscus sinensis

Abstract A feeding trial was conducted to evaluate the effects of dietary vitamin C level on the growth, liver lipid oxidation, and carapace strength of juvenile soft-shelled turtles, Pelodiscus sinensis. Seven experimental diets containing 0–619 mg vitamin C/kg were fed to 140 individually reared soft-shelled turtles with an average weight of 4.3 ± 0.07 g for 8 weeks. There was no significant difference (p > 0.05) in weight gain, feed conversion ratio, protein efficiency ratio, and muscle composition among turtles fed different test diets. Muscle composition was as follows: moisture, 73.5%; crude protein, 18.3%; lipid, 2.82%; and ash, 0.73%. Hepatic vitamin C concentration, liver tissue lipid oxidation, carapace strength, and carapace collagen content in turtles fed the vitamin C-free diet were the lowest among the dietary groups. The highest carapace strength was observed in turtles fed a diet containing approximately 350 mg of vitamin C/kg. Although the absence of dietary vitamin C did not impact the growth of the turtles, the supplementation of vitamin C could enhance the carapace strength and collagen content of the soft-shelled turtles. Analyzed by a polynomial regression, the estimated dietary vitamin C level for optimal carapace collagen and strength of the soft-shelled turtles was approximately 370–380 mg/kg.

Estimation of dietary vitamin A requirement of juvenile soft-shelled turtle,Pelodiscus sinensis

A feeding trial was conducted to evaluate the dietary vitamin A requirement of the soft-shelled turtle Pelodiscus sinensis. Turtles with an approximate body weight of 6.8 g were fed diets containing 0–4.58 mg kg−1 (15 251 IU) vitamin A (retinyl acetate) for 8 weeks. Turtles fed diets without vitamin A showed the lowest growth performance. The animals gradually gained weight when dietary vitamin A increased from 0 to 3.6 mg kg−1. Liver vitamin A gradually increased with supplementation of dietary vitamin A of up to 2.7 mg kg−1. Beyond this concentration, the vitamin A in the liver significantly increased. Data analysis using a polynomial regression or exponential model showed that the estimated dietary vitamin A requirement for juvenile soft-shelled turtles based on weight gain, red blood cell count and liver vitamin A measurements was 3.48, 2.84 and 2.58 mg kg−1, respectively.

Partial replacement of fish meal by soy protein concentrates in diets for a new Japanese strain of juvenile soft-shelled turtle,Pelodiscus sinensis

An 8-week experiment was conducted to evaluate the effects of dietary fish meal (FM) replaced by soybean protein concentrate (SPC) on Japanese strain of soft-shelled turtle, Pelodiscus sinensis juveniles. Diets were formulated to replace FM protein by SPC at 0, 15, 30, 45, 60 or 60% supplemented with phytase (2000 FTU kg−1) (designated as S0, S15, S30, S45, S60 and S60P, respectively), and each diet was fed to triplicate groups. The results showed that the growth was significantly lower when dietary SPC replaced more than 45% FM. The turtles fed the S15 or S30 diet showed comparable feed and protein utilization efficiency compared with the S0 group, whereas more than 30% replacement of FM adversely affected these values. Increasing dietary SPC levels significantly lowered the apparent digestibility coefficients (ADC) of dry matter, protein, lipid, phosphorus and gross energy. Whole-body protein, ash and phosphorus content showed a declining trend when dietary SPC levels increased, while body lipid and moisture content were unaffected. When the turtles were fed diets with increasing levels of SPC, serum total protein concentration, alkaline phosphatase and catalase activities decreased with a corresponding increase in glutamic pyruvic transaminase activity. Turtles fed the S60P diet showed comparable growth performance and feed utilization efficiency to the S40 group, and were superior to the S60 group. The present study showed that SPC could successfully substitute for 30% FM protein in the diets for P. sinensis juveniles, and the maximum effective substitution may be greater if exogenous phytase was added.

Protein-sparing effects and LPL gene expressions of dietary lipids in the juvenile soft-shelled turtle,Pelodiscussinensis

The aim of this study was to evaluate the effects of dietary lipids on protein-sparing and lipoprotein lipase (LPL) mRNA expression in culture using 360 juvenile soft-shelled turtles (Pelodiscussinensis) (initial weight 4.26 ± 0.14 g). The turtles were allotted to six diets with three duplicates for 60 days. A control diet with 46% protein and 55% fishmeal (CD) and five isonitrogenous diets with 41.3% protein and 45% fishmeal (F, S, L1, L2 and L3) were used, containing the following three lipid types: fish oil, soybean oil and mixed oils (soybean oil: fish oil = 1:1). The results showed that the survival rate was not affected by dietary lipids (P > 0.05). The highest weight gain and lowest feed coefficient ratio were seen in the L3 diets (P < 0.05). Turtles fed with L2 and L3 diets had lower superoxide dismutase activities, higher alanine aminotransferase activities and higher cholesterol concentrations than those exposed to other diets (P < 0.05). Hepatic LPL activity and LPL mRNA expression were higher in the L3 diets than in the other diets (P < 0.05). Overall, there were obvious protein-sparing effects of dietary lipids and LPL mRNA expression was stimulated by high dietary lipids in soft-shelled turtles in this study.

Dietary magnesium requirement of soft-shelled turtles, Pelodiscus sinensis, fed diets containing exogenous phytate

A feeding study was conducted to evaluate the effects of an exogenous phytic acid diet on the dietary magnesium (Mg) requirement for soft-shelled turtles. Juvenile soft-shelled turtles, Pelodiscus sinensis, were fed diets that contained 36, 160, 357, 630, 947, 1249, or 1560 mg/kg Mg and 11 g/kg of phytic acid for 8 weeks. Weight gain of turtles generally increased as dietary Mg increased up to approximately 630 mg/kg followed by a plateau stage till 1560 mg/kg. The plasma alkaline phosphatase (ALP) activity, carapace strength and concentration of Mg in the tissue generally increased as dietary Mg concentrations increased from 36 to 947 mg/kg. However, increases in Mg beyond 947 mg/kg caused the Mg concentrations in the tissue and carapace strength to remain constant. When 11 g/kg of phytic acid was added to the diet and broken-line analysis used weight gain as the indicator, the dietary Mg requirements for soft-shelled turtles was estimated at 715 mg/kg. This is a 10% increase from the requirement reported for turtles fed a phytate-free diet. A dietary intake of 970 mg Mg/kg is recommended to further enhance carapace strength and plasma ALP activity in soft-shelled turtles.

Effects of dietary magnesium on the growth, carapace strength and tissue magnesium concentrations of soft-shelled turtle,Pelodiscus sinensis(Wiegmann)

A feeding trial was conducted to evaluate the effects of dietary magnesium on the growth, carapace strength, tissue and serum Mg concentration of soft-shelled turtles, Pelodiscus sinensis (Wiegmann). Juvenile soft-shelled turtles of approximate 5.4 g body weight were fed diets with seven levels of Mg (48, 206, 369, 670, 955, 1195 and 1500 mg Mg kg−1) for eight weeks. No significant difference (P ≥ 0.05) was found in weight gain (WG), feed conversion ratio or protein efficiency ratio among treatments. However, the WG of turtles continued to increase with increasing dietary Mg levels up to 670 mg kg−1, beyond which the WG levelled off. The plasma alkaline phosphatase activity and the muscle, bone Mg concentrations of the turtles increased with the increasing dietary Mg levels between 48 and 955 mg kg−1, beyond which the tissue Mg concentrations remained relatively constant. Furthermore, the carapace strengths of turtles fed with the control diet of 48 mg Mg kg−1 were significantly weaker (P < 0.05) than that of turtles fed with diets containing higher Mg levels. Based on a broken-line modelling analysis, the required dietary Mg level for the optimal WG of juvenile soft-shelled turtles was estimated to be approximately 650 mg kg−1. By contrast, the required dietary Mg levels for turtles to reach the optimal muscle and bone Mg concentrations were 1050 and 1000 mg kg−1 respectively. The required dietary Mg level for maximal alkaline phosphatase activity was approximately 980 mg kg−1.

Efficacy and tolerance of lutein as colourant in diet of juvenile soft-shelled turtlePelodiscus sinensis

The effects of dietary supplementation of lutein on the growth, haematological profile and pigmentation in target tissues of the soft-shelled turtles were investigated. Five experimental diets were prepared with lutein levels at 1.16 (D1, control), 70.3 (D2), 132 (D3) and 239 (D4) mg kg−1, and one more high inclusion level of 3410 mg kg−1 (D5) was included for tolerance test. Each diet was fed to 24 juvenile turtles for 8w. Specific growth rate (SGR) in D2, D3 and D4 was significantly higher than that of group D1 and D5. Skin yellowness (b*) and chroma (C*) of both carapace and plastron skin were all significantly increased with higher dietary lutein levels. Dietary lutein supplementation turned the H° values of skins into yellowness. The accumulation of lutein in skin and muscle also augmented significantly with increasing lutein levels and fit a logarithmic correlation with dietary lutein levels. There were almost no differences in haematological parameters of all turtles. Lutein is an efficient and safe colourant in diet of soft-shelled turtle. The optimal inclusion levels for the highest SGR and desired skin colour in carapace and plastron of soft-shelled turtle were 162, 142 and 143 mg kg−1, respectively.

Ontogenic development of digestive enzyme activities in juvenile soft-shelled turtle (Pelodiscus sinensis) under cultured conditions

The study was conducted to investigate the ontogenic development of main digestive enzymes (pepsin, trypsin, amylase and lipase) activities in juvenile soft-shelled turtle (Pelodiscus sinensis) (initial mean bodyweight 3.63±0.27 g), in order to provide data on the digestive physiology of the juveniles during the first 30 days after hatching (DAH). The soft-shelled turtles were reared in an indoor rearing system, and fed with a formulated diet four times daily from 2 to 30 DAH. The results showed that the specific growth rate (SGR) of soft-shelled turtle ranged from 1.31 to 4.00%/d during the first 30 DAH. The specific activities of pepsin in stomachic segments, trypsin, amylase and lipase in intestinal segments first decreased slightly then increased to the maximum value (P < 0.05). The specific activities of these enzymes were first detected on 1 DAH, and the lowest values were observed from 4 to 6 DAH, while the highest values were found from 22 to 30 DAH. Results of the present study indicated that the activities of digestive enzymes in soft-shelled turtle developed during the development and were well correlated with growth.

Effect of protein restriction with subsequent re-alimentation on compensatory growth of juvenile soft-shelled turtles (Pelodiscus sinensis)

The effects of protein restriction with subsequent re-alimentation on compensatory growth (CG) of juvenile soft-shelled turtles (Pelodiscus sinensis) were investigated. The turtles were fed five diets containing different crude protein content (T1: 29.24%, T2: 31.42%, T3: 34.19%, T4: 37.16%, C: 43.31%), while the energy content remained constant for 4 weeks (restriction period) and then re-fed a diet (43.31% crude protein) for 7 weeks (re-alimentation period). During the restriction period, feed conversion ratio (FCR) significantly increased in all protein-restricted groups (T1–T4) compared with the control group (C). At the end of the restriction period, body mass in groups T1 and T2 was significantly lower than that in the control group. During the re-alimentation phase, weekly body mass gain in group T1 was greater than that of the control from week 5 to week 10. FCR significantly decreased in group T1 compared with the control. No significant differences in final body mass between C and T1 groups were found at the end of the re-alimentation period. These results indicated that soft-shelled turtles receiving a diet in which protein was reduced from 43.31 to 29.24% (approximate 33% reduction) for 4 weeks achieved a 6 week complete CG response.

Aphanomyces sinensis sp. nov., isolated from juvenile soft-shelled turtle, Pelodiscus sinensis, in Japan

A species of Aphanomyces was isolated from juvenile soft-shelled turtles, Pelodiscus sinensis, cultured in Japan. Typically, an infected turtle showed small whitish maculae on the carapace. Many hyphae were observed in the epidermis. The hyphae were isolated using glucose– yeast (GY) agar plates. The morphological characteristics were very similar to those of Aphanomyces laevis, but a clear nuclear spot was observed in the center of the oospore in the strains isolated from the soft-shelled turtles. The optimal growth temperature for the isolates was 25–30°C and the optimum pH was 6–9. Experimental infection tests with isolates produced small whitish maculae on the carapace, and soft-shelled turtles artificially infected with the zoospores showed high mortality, especially in the highdose group. Phylogenetic analysis based on the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) indicated that the isolates from the soft-shelled turtles were unidentified species of Aphanomyces. As a result, the strain was described as a new species, Aphanomyces sinensis.

Effects of dietary β-carotene levels on growth and liver vitamin A concentrations of the soft-shelled turtle, Pelodiscus sinensis (Wiegmann)

A feeding trial was conducted to evaluate the effect of dietary β-carotene level on the growth and liver vitamin A concentrations in soft-shelled turtles, Pelodiscus sinensis, fed a vitamin A-free diet. Soft-shelled turtles were fed diets containing 0, 14.5, 26.5, 47.5, 87.3, 112.8 and 163.8 mg β-carotene kg−1 for 10 weeks. Although it was not statistically significant due to high deviation within each group, mean weight gain of soft-shelled turtles fed the diet without β-carotene supplementation was the lowest among all test groups. Vitamin A concentrations in liver of turtles significantly (P<0.05) increased when dietary β-carotene level reached 47.5 mg kg−1 indicating that soft-shelled turtles were capable of converting β-carotene to vitamin A. Analysed by regression modelling, dietary β-carotene levels for optimal growth and maximal liver vitamin A contents of juvenile soft-shelled turtles fed the vitamin A-free diets were 49.1 and 88.7 mg kg−1 respectively.