Molting Frequency Research Articles

Dietary phospholipid alleviates the adverse effects of high-lipid diet in Chinese mitten crab (Eriocheir sinensis)

An 8-week feeding trial was conducted to investigate the impacts of dietary phospholipid (PL) on growth, antioxidant status and lipid metabolism of Eriocheir sinensis juveniles (0.53 ± 0.01 g) fed four diets including high lipid (13%, HL) and low lipid (8%, LL) and each lipid level containing either high PL (5%, HP) or low PL (1%, LP). Final weight, weight gain, specific growth rate and molting frequency in the HL-LL group were lower than those in the HL-HP group. Compared with the HL-LP group, the enzymatic antioxidant activities increased and hepatopancreatic malondialdehyde content decreased in the HL-HP group. In addition, the high dietary PL significantly suppressed the accumulation of lipid in the hepatopancreas and the whole-body induced by high lipid diets. Quantitative real-time PCR showed that the dietary PL reduced excessive lipid deposition in the hepatopancreas through promoting lipid oxidation and exportation as well as inhibiting lipid absorption and synthesis at the transcriptional level. This study indicates that high dietary PL could promote lipid utilization in E. sinensis fed a high-lipid diet by optimizing lipid metabolism to improve growth performance.

Fresh or formulated: A preliminary evaluation of fresh blue mussel (Mytilus galloprovincialis) and formulated experimental feeds with inclusion of fresh blue mussel on the growth performance of hatchery-reared juvenile slipper lobster (Thenus australiensis)

Following recent advances in hatchery technology and large-scale larval rearing of spiny and slipper lobsters, a greater understanding of key nutritional requirements is now imperative to facilitate feed development for juvenile culture. However, there is a lack of relevant information available for the slipper lobsters, particularly Thenus species. This study sought to evaluate the potential requirements for and effects of a fresh ingredient component in a formulated feed on the growth performance of hatchery-reared juvenile Thenus australiensis. This was assessed using six formulated experimental feeds incorporating fresh blue mussel flesh (BM; Mytilus galloprovincialis) in a geometric series (0, 1.6, 3.1, 6.3, 12.5 and 25.0% dry matter) administered continuously over 9 weeks. An additional dietary treatment of blue mussel half shells (BMHS) was included as a reference feed to establish a benchmark of growth potential. Survival and moult frequency were unaffected by feed treatment. Lobsters fed BMHS displayed a clustered or synchronised moulting pattern with two major moulting events lasting several days each during the experiment. In contrast, lobsters provided experimental feeds moulted continuously throughout the experiment. The BMHS produced approximately 2-fold greater growth compared to experimental feeds, while BM incorporated into experimental feeds had no beneficial effect on growth at any inclusion level. Growth mirrored feed intake where it was also found that feed intake on a dry matter basis was approximately 2-fold higher for BMHS compared to experimental feeds, while biological feed conversion ratios were similar for all feeds. Thus, dry matter intake appeared to be primarily responsible for the difference in growth rates achieved. Bulk chemical analysis revealed that BMHS-fed lobsters had significantly lower ash content coupled with higher gross energy, total lipid and polar lipid contents on a proportional basis compared to lobsters fed formulated experimental feeds. Lobster haemolymph Brix values were also significantly higher in the BMHS treatment lobsters. Higher Brix coupled with decreasing feed intake suggests these lobsters were on average at a more advanced stage within the moult cycle and offers a possible explanation for differences in body chemistry. In conclusion, while growth rates were lower in animals fed formulated feeds compared to benchmark growth performance, overall survival, moulting and growth performance revealed the potential of the basal experimental feed formulation as a reference for future nutrition research with this species without a requirement for inclusion of fresh BM. The research highlights that significant opportunities exist to improve slipper lobster growth performance through maximising feed intake.

Effect of dietary phosphorus on growth performance, body composition, antioxidant activities and lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis)

This study investigated the effects of dietary phosphorus (P) on growth, body composition, antioxidant activities and lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis). Six diets containing available P levels at 0.20%, 0.44%, 0.99%, 1.37%, 1.75% and 2.01% were prepared and fed to juvenile E. sinensis (0.38 ± 0.01 g) for 56 days. The weight gain, specific growth rate and molting frequency were markedly affected by dietary P, and the highest weight gain and specific growth rate were obtained in crabs fed the 0.99% available P diet. With increasing the dietary available P levels, the whole-body ash, Ca, and P contents, as well as the hepatopancreas and serum P contents increased, while the whole-body Mg content decreased. The increase of dietary P levels significantly decreased the lipid contents of whole-body, hepatopancreas and muscle, while increased the crude protein content of hepatopancreas. The hepatopancreas and serum alkaline phosphatase activities increased with an increase in dietary available P levels from 0.20% to 1.37%, and then decreased afterward. The crabs fed 1.37% available P diet had a markedly higher alkaline phosphatase activity than those fed 0.20%, 0.44% and 2.01% available P diets. Moreover, dietary P significantly affected total antioxidant capacity, the activities of total superoxide dismutase and glutathione peroxidase, and the malondialdehyde content in the hepatopancreas. The highest antioxidant activity and lowest malondialdehyde content in the hepatopancreas were found in the crabs fed 1.37% of available P in the diet. The relative mRNA expression showed that dietary P reduced hepatopancreas lipid accumulation might be produced through suppressing the genes related to lipid synthesis and promoting the genes related to lipid transport. This study demonstrates that optimum dietary P could enhance growth, antioxidant capacity and reduce hepatopancreatic lipid accumulation in juvenile E. sinensis and the range of available P in the diet is suggested to be 1.16%–1.51%.

Evaluation of boscalid toxicity on Daphnia magna by using antioxidant enzyme activities, the expression of genes related to antioxidant and detoxification systems, and life-history parameters

Boscalid is a succinate dehydrogenase inhibitor fungicide commonly used to control a range of plant pathogens. Although it is one of the most common fungicides in the aquatic environment, the potential adverse effects of boscalid on freshwater invertebrates still remain unclear. This study aimed to evaluate the toxicity of boscalid on Daphnia magna (D. magna) and provide new information to assess the eco-toxicity of the boscalid on aquatic invertebrates. The effects of boscalid on malondialdehyde (MDA) level, activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) and the mRNA level of genes associated with antioxidant system (sod, cat, and gst) and detoxification (cytochrome P450 4 (cyp4) and nuclear respiratory factor 1 (nrf1)) were determined after 48 h treatment. The effect of boscalid on reproduction and development of D. magna was evaluated by a 21-d-chronic toxicity test. Boscalid dose-dependently altered activities of SOD, CAT, and GST and led to lipid peroxidation during acute exposure in D. magna. Exposure to 5 and 10 mg/L boscalid also significantly decreased gene expression of sod, gst, cyp4 and nrf1 but increased cat gene expression. Furthermore, chronic toxicity results showed that exposure to boscalid decreased molting frequency, number of neonates per Daphnia, and the number of broods per female as compared to the control groups. The above results indicated that boscalid had significant negative impacts on D. magna, and information present here helps to evaluate the eco-toxicity caused by boscalid on aquatic invertebrates.

Effects of dietary lipid levels on survival, growth performance, and antioxidant ability of the early juvenile Scylla paramamosain

Five isonitrogenous diets (50% crude protein) with 7%, 9%, 11%, 13%, and 15% lipid levels (named as L7, L9, L11, L13, and L15, respectively) were designed to evaluate the effects of dietary lipid levels on survival, growth performance, body composition, and antioxidant ability of the early juvenile Scylla paramamosain. Each diet was fed to three replicates of 28 crabs with initial weight 42.23 ± 0.21 mg for 8 weeks. Crabs fed diet with lowest dietary lipid level (L7 group) obtained significantly lower survival than other crabs. The highest final body weight (FBW), weight gain (WG), specific growth rate (SGR), and molting frequency (MF) were observed in L11 group. Meanwhile, the highest mRNA expression of ecdysone receptor (EcR) also observed in L11 group. Besides, a positive correlation between body lipid contents and dietary lipid levels was observed in present study. But the mRNA expression of fatty acid synthetase (FAS) was relatively lower in L15 group. In the hepatopancreas, superoxide dismutase (SOD) activity significantly increased with increasing dietary lipid levels. On the contrary, the concentration of malondialdehyde (MDA) significantly decreased with elevating dietary lipid levels (except L15 group). Meanwhile, the lowest catalase (CAT) activity appeared in L7 group, but there was no statistical difference from other groups. Through the second order polynomial regression equation analysis of WG, the optimum dietary lipid level in the early juvenile S. paramamosain was 10.31%.

Life History of an Invasive Population of Allegheny Crayfish (Faxonius obscurus) in an Eastern Pennsylvania Stream

Crayfish are key components of North American aquatic ecosystems, but information about their life history is typically lacking or incomplete. No such data are available for invasive populations of Faxonius obscurus (Allegheny Crayfish) in eastern Pennsylvania. I studied the life history of an invasive population in a small tributary in the Susquehanna River drainage of eastern Pennsylvania. Life-history characteristics (i.e., size at sexual maturity, sex ratios, seasonal shifts between reproductive and non-reproductive form in males, glair development, timing of ovigerous females, molting frequency, and size classes) were similar to those reported for many members of the genus Faxonius and largely similar to those reported for populations of Allegheny Crayfish across their native range. However, realized fecundity was greater than reported in West Virginia populations. Female body length was a predictor of realized fecundity, differing from southern populations of this species.

ANALYSIS OF WATER SALINITY LEVEL OF FREQUENCY MOLTING IN VANNAMEI SHRIMP (LITOPENAEUS VANNAMEI) ABLATED

Media salinity is a masking factor that plays an important role in controlling the process of shrimp molting and osmoregulation. Both of them are ecophysiological factors for shrimp life, so it is necessary to know the optimum level or range of media salinity for each phase of the molting phase changes in the stage and osmoregulation phase. This study was conducted to examine the molting frequency of adult L. vannamei which was ablated and cultivated at various levels of salinity. This research was carried out for 60 days. This study uses experimental laboratory methods with a systematic randomized design (RAS) with 4 treatments and 3 replications in each treatment. The treatments tested were salinity with S1 treatments (10 ppt, 289.20 mOsm / l postmolt H2O isosmotic), S2 (15 ppt, 432.80 mOsm / l H2O initial intermolt isosmotic), S3 (25 ± 1 ppt, 725, 15 mOsm / l H2O isosmotic final intermolt) and S4 (29 ± 1 ppt, 820.10 mOsm / l H2O isosmotic molt). Data were analyzed with ANOVA. Meanwhile, the difference in effect between treatments was obtained through Duncan's multiple area test. ANOVA results showed that various levels of isoosmotic media salinity at various molting phases had an influence (p <0.05) on molting frequency. The best value of molting frequency was in the S4 treatment (29 ± 1 ppt) (close to isoosmotic molt) 10 times. In the maintenance of L. vannamei which is affixed, it should pay attention to the needs of isoosmotic media, namely media with a salinity of 25 ± 1-29 ± 1 ppt (final intermolt isoosmotic range / premolt to molt). the difference in effect between treatments was obtained through Duncan's multiple region test. ANOVA results showed that various levels of isoosmotic media salinity at various molting phases had an influence (p <0.05) on molting frequency. The best value of molting frequency is in the treatment of S4 (29 ± 1 ppt) (close to isoosmotic molt) 10 times. In the maintenance of L. vannamei which is affixed, it is better to pay attention to the needs of isoosmotic media, ie media with a salinity of 25 ± 1-29 ± 1 ppt (final intermolt isoosmotic range / premolt to molt). the difference in effect between treatments was obtained through Duncan's multiple region test. ANOVA results showed that various levels of isoosmotic media salinity at various molting phases had an influence (p <0.05) on molting frequency. The best value of molting frequency is in the treatment of S4 (29 ± 1 ppt) (close to isoosmotic molt) 10 times. In the maintenance of L. vannamei which is affixed, it is better to pay attention to the needs of isoosmotic media, ie media with a salinity of 25 ± 1-29 ± 1 ppt (final intermolt isoosmotic range / premolt to molt). The best value of molting frequency was in the S4 treatment (29 ± 1 ppt) (close to isoosmotic molt) 10 times. In the maintenance of L. vannamei which is affixed, it is better to pay attention to the needs of isoosmotic media, ie media with a salinity of 25 ± 1-29 ± 1 ppt (final intermolt isoosmotic range / premolt to molt). The best value of molting frequency is in the treatment of S4 (29 ± 1 ppt) (close to isoosmotic molt) 10 times. In the maintenance of L. vannamei which is affixed, it is better to pay attention to the needs of isoosmotic media, ie media with a salinity of 25 ± 1-29 ± 1 ppt (final intermolt isoosmotic range / premolt to molt). Keyword : Salinity, Osmoregulation, Molting, L. vannamei, Ablation.Â

The Effects of Using Different Levels of Calcium Carbonate (CaCO3) on Growth, Survival, Molting Frequency and Body Composıtion of Freshwater Crayfısh Juvenile, Pontastacus leptodactylus (Eschscholtz, 1823)

The present study was conducted to determine different calcium carbonate (CaCO3) level effects on growth, survival, molting frequency and body composition of freshwater crayfish juvenile, Pontastacus leptodactylus (Eschscholtz, 1823). Initial mean weight and length juvenile crayfish were measured to be 0.53±0.01 g and 22.0±0.05 mm, respectively. Crayfish were stocked randomly in twelve aquariums in area of 0.2 m2 at the rate of 50 crayfish/m2. The different level of CaCO3 was added into a commercial trout diet (Control), 3%, 6% and 12% for feeding the juvenile crayfish. After 90-day study, supplementation of CaCO3 significantly (P< 0.05) did affect growth rate, specific growth rate, feed intake, molting frequency, biomass, but reduced survival of crayfish at level of 6% diet as compared to the other groups. The proximate composition of tail meat of crayfish was unaffected by the diet. These results indicated that the calcium carbonate addition is required for crayfish. At the end of the experiment, 6% of calcium carbonate was suggested to be used in formulated diets for crayfish juvenile.

Paracetamol affects the expression of detoxification- and reproduction-related genes and alters the life traits of Daphnia magna.

Paracetamol (APAP) is a widely used non-steroidal anti-inflammatory drug and has been frequently detected in aquatic environment. However, limited information is provided about the toxic effects and detoxification mechanism of APAP in aquatic invertebrates. In the present study, the change of life traits of Daphnia magna (e.g., body length, growth rate and reproduction) was investigated under the chronic APAP exposure (0-5000 μg/L) for 21 day, and the effects of APAP on the expression of the detoxification- and reproduction-related genes including HR96, CYP360A8, CYP314, MRP4, P-gp, EcR and Vtg in the acute exposure (up to 96 h) were also determined. Results showed that the molting frequency, days to the first brood and days to the first egg production of D. magna were affected under the 50 μg/L concentration of APAP in the chronic exposure test. In the acute test, the transcriptional expression of HR96 was up-regulated under APAP exposure for 24 and 48 h. Similar performances were also observed in the expression of CYP360A8, CYP314, MRP4 and P-gp. However, with exposure time extended to 96 h, the induction of HR96 decreased or even reversed in some cases. It may indicate that the defense system in Daphnia is activated for a short time of exposure or becomes adaptive after longer term of exposure. APAP exposure also affected reproduction-related genes expression, which was related to the exposure time and concentration of APAP. In summary, APAP significantly affected the expression of genes associated with detoxification metabolism and altered some physiological parameters in D. magna.

English

Abstract Counting bands via the gastric mill is a potential direct approach for ageing crayfish; however, the validity of ageing crustaceans using the gastric mill is unknown. Our study objectives were to 1) compare gastric mill age estimates to a traditional aging technique, 2) compare ageing precision among the ossicles, and 3) examine the effects of temperature on gastric mill band formation. From 2017–2018, we collected 681 ringed crayfish Faxonius neglectus neglectus (Faxon) from ten Ozark Highland streams. Our length-frequency analysis reflected seven age classes, whereas gastric mill age estimates indicated individuals were up to 10 yr of age. The length-frequency analysis age estimates showed good congruence (± 1 yr) with age estimates from the gastric mill 78% of the time. The coefficient of variation (CV) of age estimates from gastric mill bands between our readers was 29.7%. Ageing precision was highest when using the zygocardiac ossicles (CV = 12.4%). Gastric mill age estimates for known age-1 crayfish from a thermally stable laboratory were not significantly different from one, whereas age estimates from a thermally varying laboratory were greater than one. Our results indicate molting frequency does not control gastric mill band formation, and temperature plays a role in band formation.

The effect of dietary protein, lipid, and carbohydrate levels on the performance, metabolic rate and nitrogen retention in juvenile European lobster (Homarus gammarus, L.)

Releasing hatchery-reared juveniles in the wild can mitigate the general decline in the natural stocks of European lobster, Homarus gammarus, L.. However, growth and survival rates in lobster culture are low, presumably due to suboptimal nutrition and feeding. With the aim of determining appropriate nutrient levels, we tested different formulated extruded feeds for the culture of juvenile European lobster. Baseline metabolism (standard metabolic rate, SMR), in combination with the metabolic cost of feeding (specific dynamic action, SDA), and nitrogen retention during digestion and assimilation was investigated for six experimental diets. Diets were formulated to contain two different levels of protein (400 and 500 g kg−1), with three lipid to carbohydrate (L:CHO) ratios (low, medium, and high). These experimental diets were tested over a 32-day period, against a conventional control diet (Antarctic krill, Euphausia superba). During this period, the growth performance of the juveniles was assessed as molting frequency, increments in carapace length and whole body wet weight. At the end of the growth performance trial, oxygen consumption (MO2) and nitrogen excretion rates of individual lobsters were determined prior to and following the ingestion of a single meal. Molting occurred more frequently in juveniles fed with krill and krill resulted in a significantly higher specific growth rate than experimental dry feeds except for the 500-low diet. However, lobsters fed any of the three 500 and the 400-low diets had carapace length increments, SMR, SDA, and nitrogen retention similar to those fed the krill diet. Results suggest that protein is an important macronutrient for juveniles of this species and must be included above 40%. Also, lobsters have a dietary requirement for carbohydrates ranging from 24% to 35% probably related to the need for glycogen in chitin synthesis. The lower the protein content, the higher the requirement in carbohydrates.

Comparative analysis of transcriptomes from different coloration of Chinese mitten crab Eriocheir sinensis

Chinese mitten crab Eriocheir sinensis is probably the most important freshwater cultured crab in China. A tiny minority of brownish-orange individuals have been discovered in the long period of artificial breeding history of E. sinensiss. Those mutants are usually accompanied with slow growth rate, low molting frequency and poor survival rate, which may be the results of growth defects and immunodeficiency. To better understand the relationship between body color determination and the immune system as well as the related genes expression in E. sinensiss, we performed the whole-body transcriptome analysis in different color of first stage zoea (ZI) larvae using next-generation sequencing (NGS) technology. We randomly assembled 175.40 and 177.52million clean reads from the wild and mutant ZIs, respectively. Finally, we identified 7153 differentially expressed genes (DEGs) (p < 0.05), with 5194 up-regulated and 1959 down-regulated. A total of 13 KEGG pathways related to immune system were detected among 248 pathways. Except the first whole-body RNA sequencing of color-specific transcriptomes for E. sinensis, this study will offer a better understanding of the underlying molecular mechanisms of interaction between color determination and the immune system.

Effects of stocking density and artificial macrophyte shelter on survival, growth and molting of juvenile red swamp crayfish (Procambarus clarkii) under experimental conditions

Optimizing stocking density and increasing shelters have been thought as strategies to enhance the performance of crayfish culture. In this study, indoor controlled experiments were carried out to determine the effects of different levels of stocking density (i.e., 50, 100 and 150 ind.·m−2) and artificial macrophyte coverage (i.e., 20%, 50% and 80%) on the survival, growth and molting of juveniles of red swamp crayfish (Procambarus clarkii). A total of nine treatments with four replications were conducted simultaneously in 36 aquariums. No significant interactions were found between stocking density and artificial macrophyte coverage (P > 0.05). The crayfish yield (total biomass, TB) at 150 ind.·m−2 was significantly higher than that at 50 or 100 ind.·m−2 (P < 0.05), while higher stocking densities showed negative effects on the growth. A stocking density of 50 ind.·m−2 led to a significantly higher survival rate (SR), total weight gain (TWG) and mean molting frequency (MMF) (P < 0.05), and the specific growth rate of weight (SGRw) at 50 and 100 ind.·m−2 was significantly higher than that at 150 ind.·m−2 (P < 0.05). The rates of cheliped injury (CIR) and shelter occupancy (SO) were not significantly correlated to stocking density. Artificial macrophyte coverage had no significant effect on the SR or CIR, while the TB and MMF at 80% coverage were significantly higher than those at 20% coverage. The TWG, SGRw and SO (daylight) at 50% and 80% coverage were significantly higher than those at 20% coverage. Overall, these results indicate that, under improved culture conditions, a stocking density of around 50 ind.·m−2 and around 50% coverage of artificial shelter can be optimal for indoor culture of juvenile P. clarkii.

Novel method of tagging the kuruma prawn Penaeus japonicus with a trans-molting retentive external eye (TRAMORE) tag

An easily applicable, economical, and reliable tagging method, without risk to consumers, is required for the kuruma prawn Penaeus japonicus. This report describes the development of external tags for the kuruma prawn. Two types of external tag, differing slightly in form, were developed. Tests were performed to determine whether these external tags were retained after molting and whether the tagging method affected survival and growth in the laboratory. One type of external tag, with a hole of diameter 1.5 mm, was applied to the eyestalks of juvenile prawns approximately 45 mm in body length (BL). Despite repeated molting, these tags were retained at least until the prawns grew to BL 140 mm. Therefore, these tags were called trans-molting retentive external eye (TRAMORE) tags. The trackable size range with the TRAMORE tag, with a hole of diameter 1.5 mm, (<140 mm BL) covered approximately 50 % of kuruma prawns caught in Seto Island Sea, Japan, one of its main fishing grounds. The TRAMORE tag had no impact on the survival, growth, or molting frequency of juveniles. The second type of TRAMORE tag, with a hole of diameter 2.8 mm, was not shed during molting of individuals of BL ranging from 82.7 mm to 216 mm BL. Approximately 100 % of kuruma prawns caught in Seto Island Sea were of this size. The TRAMORE tag would contribute to kuruma prawn stock enhancement programs and investigations of key aspects of its ecology.

Influence of dietary phospholipid on growth performance, body composition, antioxidant capacity and lipid metabolism of Chinese mitten crab, Eriocheir sinensis

This study determines the effects of level and source of dietary phospholipid (PL) on growth performance, body composition, antioxidant capacity and lipid metabolism in juvenile Chinese mitten crab, Eriocheir sinensis. One control diet (PL-devoid) and six test diets containing three PL types (soybean lecithin, egg yolk lecithin, and krill oil) at two levels (1% and 3%) each were formulated to feed E. sinensis juveniles (0.26 ± 0.01 g) for 8 weeks. Final body weight, specific growth rate, weight gain and molting frequency significantly increased in the PL supplementation groups, and the crabs fed 3% krill oil showed the best growth performance. The total lipid of whole body was significantly lower in the PL supplementation groups than that in the control. With PL supplementation, the specific activities of superoxide dismutase and catalase in the hepatopancreas markedly increased, while malondialdehyde decreased. In addition, total lipid and triglyceride contents in the hepatopancreas significantly decreased in the PL supplementation groups. Real-time quantitative PCR revealed that dietary PL reduced hepatic lipid accumulation probably through inhibiting lipid synthesis related genes and promoting lipid export related genes at the transcriptional level. This study indicates that krill oil is an excellent PL source and the diet with 3% PL can improve growth performance, increase antioxidant capacity and promote lipid utilization for juvenile E. sinensis.

Acute and chronic effects of thifluzamide on Daphniamagna

Thifluzamide is a thiazole carboxanilide fungicide used to control a wide range of basidiomycete diseases on maize, potatoes, rice, and other crops. Although this fungicide is found in aquatic environments, there is no information about its acute and chronic toxicity on aquatic invertebrates. In the present study, to investigate acute and chronic toxicity of thifluzamide, daphnids were exposed to 1.25, 1.5, 2, and 2.5 mg/L thifluzamide for 48 h and 21 days, respectively. The expression of four oxidative stress-related genes (CAT, GCLC, GST, and GPX) and life-history parameters such as days to the first brood, days to the first egg production, and molting frequency were measured. The results showed that exposure to thifluzamide for 48 h significantly induced the expression of oxidative stress-related genes in D. magna. A dose-dependent relationship was obtained for mRNA levels of CAT and GST. In the 21-day chronic toxicity test, a concentration-dependent decrease was observed for the number of neonates per Daphnia, the number of broods per female, and molting frequency. Additionally, the first brood day and the first egg production day were significantly (P < 0.05) delayed in a dose-dependent manner. The results of this study indicate that the harmful effects of thifluzamide on aquatic invertebrates cannot be ignored and further investigation is needed.

The effect of ocean acidification on the intertidal hermit crab Pagurus criniticornis is not modulated by cheliped amputation and sex

Impacts of the interactive effects of ocean acidification (OA) with other anthropogenic environmental stressors on marine biodiversity are receiving increasing attention in recent years. However, little is known about how organismal responses to OA may be influenced by common phenomena such as autotomy and sexual dimorphism. This study evaluated the long-term (120 days) combined effects of OA (pH 7.7), experimental cheliped amputation and sex on physiological stress (mortality, growth, number of molts, cheliped regeneration and startle response) and energy budget (lipid and calcium contents) in the intertidal sexually-dimorphic hermit crab Pagurus criniticornis. Crabs exposed to OA reduced survivorship (46%), molting frequency (36%) and lipid content (42%). Autotomised crabs and males molted more frequently (39% and 32%, respectively). Males presented higher regeneration (33%) and lower lipid content (24%). The few synergistic effects recorded did not indicate any clear pattern among treatments however, (1) a stronger reduction in lipid content was recorded in non-autotomised crabs exposed to low pH; (2) calcium content was higher in males than females only for autotomised crabs under control pH; and (3) autotomised females showed a proportionally slower activity recovery than autotomised males. Although our results suggest an effect of long-term exposure to low pH on the physiological stress and energy budget of Pagurus criniticornis, the physiological repertoire and plasticity associated with limb regeneration and the maintenance of dimorphism in secondary sexual characters may provide resilience to long-term exposure to OA.

Effects of different dietary lipid sources on growth performance, antioxidant enzyme activities and biochemical composition of juvenile swimming crab, Portunus trituberculatus

An 8-week feeding trial was conducted to evaluate the effects of dietary lipid sources on growth performance, antioxidant enzyme activities and biochemical composition of juvenile swimming crab Portunus trituberculatus of initial weight 2.34 ± 0.08 g. Four different diets were formulated to contain fish oil (FO), soybean oil (SO), linseed oil (LO) or palm oil (PO). The highest final body weight, weight gain, specific growth rate and molting frequency were observed in crabs fed the FO diet. Crabs fed the SO diet showed higher glutathione peroxidase, superoxide dismutase (SOD) and catalase (CAT) activities in both serum and hepatopancreas than those fed the FO diet. The lowest malondialdehyde concentration in hepatopancreas and serum were occurred at crabs fed the SO diet. Crabs fed the LO diet had significantly higher SOD and CAT activities in hepatopancreas compared with those fed the FO diet. Crabs fed the PO diet had the highest activities of fatty acid synthase and carnitine palmitoyltransferase 1 activities in hepatopancreas among all treatments. Fatty acid compositions both in hepatopancreas and muscle reflected those of diets. Overall, these findings demonstrated that physiological–biochemical characteristics and lipid metabolism were significantly regulated by different dietary lipid sources. Moreover, dietary SO and LO supplementation could improve antioxidant ability.

Contributions of egg production and egg hatching to the total toxicity of teflubenzuron in Yuukianura szeptyckii (Collembola) in soil toxicity test.

In the standard ISO soil toxicity test using Collembola, adult survival and juvenile production are the only endpoints that can be attainable. The information on egg production and egg hatching cannot be investigated in the ISO test. To overcome this limitation, in this study, the effects of teflubenzuron on life history parameters of Yuukianura szeptyckii (Collembola) were investigated with a compressed soil test. Teflubenzuron is an insect growth regulator and has a negative effect on egg production, and egg hatching process of arthropods. LC50 decreased with increases in exposure period from 6.97 mg/kg in the third week to 3.60 mg/kg in the fourth week. The EC50 for egg and juvenile production was 0.57 mg/kg and 0.26 mg/kg, respectively. The hatching rate decreased significantly from 46 to 7% as the concentration increased from 0.25 to 1.00 mg/kg, respectively, and the molting frequency was significantly affected only at > 4 mg/kg. The toxic contribution rate (TCR) was defined as the ratio of juvenile production at an exposure concentration compared with the control, and a simple life history model was developed for TCR estimations. At the lower concentrations (< 0.3 mg/kg), the hatching rate reduction was a main contributor to the total toxicity, but the adult mortality and egg production reduction were the main contributors at the higher concentrations (> 2.0 mg/kg). The contribution of egg production reduction remained relatively constant. Since collembolan populations in the soil can be composed of various developmental stages, the differences in the sensitivity to chemicals depending on the developmental stages should be included in the assessment of the toxic impact on soil ecosystems.

Effects of two juvenile hormone analogue insecticides, fenoxycarb and methoprene, on Neocaridina davidi

Juvenile hormone analogue (JHA) insecticides are endocrine disrupters that interfere with hormonal action in insects by mimicking their juvenile hormones (JH). As the structure and functions of methyl farnesoate in crustaceans are similar to those of JH in insects, exogenous JHA insecticides could have adverse effects on the development and reproduction of crustaceans. This study examined the toxic effects of two JHA insecticides, fenoxycarb and methoprene, on a freshwater shrimp model of cherry shrimp, Neocaridina davidi. Both insecticides had detrimental effects on cherry shrimp, but fenoxycarb was more toxic than methoprene. Chronic exposure to these insecticides reduced the shrimp's body length and molting frequency. Based on transcriptome annotations for N. davidi, we identified important gene homologues that were active in both insect JH biosynthetic and degradative pathways as well as JH and ecdysteroid signaling pathways. Chronic treatments with JHAs had significant effects on these genes in N. davidi. Our transcriptomic analysis showed that genes involved in the pathways related to cuticle development, serine protease activity, and carbohydrate, peptide and lipid metabolic processes were differentially expressed in shrimp exposed to JHAs. These results demonstrate the toxicity of fenoxycarb and methoprene to freshwater crustaceans and indicate the need to monitor the use of JHA insecticides.