Stocking strategies for production of Litopenaeus vannamei (Boone) in amended freshwater in inland ponds

The performance of the Pacific white shrimp Litopenaeus vannamei (Boone) under various stocking strategies was evaluated in earthen ponds filled with freshwater amended with major ions. Six 0.1‐ha earthen ponds located in Pine Bluff, AR, USA, were filled with freshwater in 2003 and 2004, and potassium magnesium sulphate added to provide 50 mg K⁺ L^?1 and stock salt added to provide 0.5 g L^?1 salinity. In 2003, three ponds either were stocked with PL₁₅ shrimp (39 PL m^?2) for 125 days of grow out or with PL₂₅ shrimp for 55 days (23 PL m^?2) followed by a 65‐day (28 PL m^?2) grow‐out period. In 2004, ponds were stocked with 7, 13 or 30 PL₁₅ m^?2 for 134 days of grow out. Salinity averaged 0.7 g L^?1 during both years, and concentration of SO₄^?2, K⁺, Ca²⁺ and Mg²⁺ was higher, and Na⁺ and Cl^? was lower in amended pond water than in seawater at 0.7 g L^?1 salinity. Potassium concentration in amended water was 52–61% of the target concentration. Shrimp yields ranged from 3449 kg ha^?1 in 2003 to 4966 kg ha^?1 in 2004 in ponds stocked with 30–39 PL₁₅ m^?2 for a 125–134‐day culture period. At harvest, mean individual weight ranged from 17.1 to 19.3 g shrimp^?1. In ponds stocked with PL₂₅ shrimp, yields averaged 988 and 2462 kg ha^?1 for the 1st and 2nd grow‐out periods respectively. Gross shrimp yield in 2004 increased linearly from 1379–4966 kg ha^?1 with increased stocking rate. These experiments demonstrated that L. vannamei can be grown successfully in freshwater supplemented with major ions to a final salinity of 0.7 g L^?1.     

Supplementation of potassium, magnesium and sodium chloride in practical diets for the Pacific white shrimp, Litopenaeus vannamei, reared in low salinity waters

The culture of Litopenaeus vannamei in inland low salinity waters is currently being practiced in various countries around the world. These environments are often deficient in key ions essential for normal physiological function, including potassium (K⁺) and magnesium (Mg²⁺). Farmers have sometimes been able to counteract ionic deficiencies in the water profile by adding mineral salts containing sources of K⁺ and Mg²⁺. The purpose of this study was to explore the possibility of correcting deficiencies of K⁺ and Mg²⁺ in the water profile with dietary supplementation of these minerals. Two separate 7‐week experiments were conducted in 4.0 g⁻¹ artificial low salinity water to evaluate the effects of mineral supplements (K⁺, Mg²⁺ and NaCl) to diets of L. vannamei reared in low salinity waters. In trial 1 seven diets were formulated (10 g NaCl kg⁻¹, 20 g NaCl kg⁻¹, 150 mg kg⁻¹ Mg²⁺, 300 mg kg⁻¹ Mg²⁺, 5 g K⁺ kg⁻¹, 10 g K⁺ kg⁻¹, and a basal diet to serve as a control). Minerals were added in the form of purified potassium chloride (KCl), magnesium chloride (MgCl₂·6H₂O) and NaCl. Trial 2 evaluated the use of a coating agent for the Mg²⁺ and NaCl treatments, while a K⁺ amino acid complex was utilized in the K⁺ treatments to reduce mineral leaching. Trial 2 was performed using similar treatment levels as trial 1. Shrimp survival and growth were assessed in both experiments. Results from trial 1 indicated no significant differences in survival, growth or percent weight gain. Results from trial 2 revealed no significant differences in survival and growth in the NaCl and Mg²⁺ treatments. However, significant differences in growth (P < 0.05) were observed when using the 10 g K⁺ kg⁻¹ treatment, suggesting that dietary supplementation of a K⁺ amino acid complex may help improve growth of the species in low salinity waters.     

Effect of different concentrations of potassium and magnesium on performance of Litopenaeus vannamei postlarvae reared in low-salinity water and a biofloc system

Effect of K⁺ and Mg²⁺ in water on the performance of Litopenaeus vannamei using bioflocs was evaluated. Control had water with K:Mg (1:4.57) and other treatments (K:Mg of 1:5.4, 1:4.65, and 1:3.77), both with salinity of 4 g/L. Initial mean weight of shrimp was 0.08 ± 0.007 g. No difference in shrimp growth performance and survival was observed (P > 0.05) except in the control. Our results suggest that it is possible to culture postlarvae of Litopenaeus vannamei in low-salinity water with bioflocs when the water has an initial potassium concentration of 30.90 ± 8.5 mg/L and magnesium of 167.0 ± 3.9 mg/L.     

Hatchery seed production of giant freshwater prawn,Macrobrachium rosenbergii using inland ground saline water in India

The suitability of inland saline water (ISW) from the Lahli‐Baniyani Fish Farm, Rohtak was investigated for the larval rearing of giant freshwater prawn (GFP), Macrobrachium rosenbergii. Six experiments were conducted. In Experiment‐I, 54% of the larvae metamorphosed to postlarvae (PL) in constituted seawater (CSW) whereas total mortality occurred at larval stages (LS)‐II and LS‐III in ISW with salinity of 12 g L^?1. Larvae survived to LS‐IV in Experiment‐II, when ISW was supplemented with K⁺~ SW. In Experiment‐III, total hardness in ISW was reduced serially, but K⁺ ~ SW was supplemented. The larvae did not survive beyond LS‐V. In Experiment‐IV, ISW was amended with different ratios of Mg²⁺/Ca²⁺ and K⁺ ~ SW. The larvae successfully metamorphosed to postlarvae with highest survival of 51.6% in Mg²⁺/Ca²⁺ ratio of 2.5. In Experiment‐V, eight larval cycles were run with water quality used in Experiment V, where all the cycles produced PL's with a survival rate of 20–67%. In Experiment VI, the larvae were reared in Mg²⁺/Ca²⁺ ratio of 2.5 and different levels of K⁺ to optimize its requirement. The ISW amended with K⁺ 80% ~ SW and Mg²⁺/Ca²⁺ ratio of 2.5 was found to be commercially suitable for the seed production of GFP.     

Effects of ambient ion concentrations on gill ATPases in fresh water eel,Anguilla anguilla

Branchial activities of Na⁺,K⁺-ATPase (ouabain sensitive), Mg²⁺ ATPase (ouabain insensitive) and kinetic analysis of high and low affinity Ca²⁺ ATPase were measured inAnguilla anguilla that had been acclimated to demineralized water (DW, Ca < 10 M), freshwater (FW, Ca = 2 mM), and Low calcium freshwater (L-Ca, Ca = 0.9 mM). Na⁺,K⁺-ATPase activity decreased while ouabain insensitive activity increased when ambient Ca²⁺ decreased. Two kinetic forms of Ca²⁺ ATPase could be resolved in each environmental condition. The stimulation coefficients of both sites or enzymes were not affected by ambient Ca²⁺ concentrations. The maximal velocity of both the high and the low affinity Ca²⁺ ATPase was increased when external Ca²⁺ was decreased during acclimation. The low affinity Ca²⁺ ATPase and the Mg²⁺ stimulated enzyme could be a non specific enzyme accepting either Ca²⁺ or Mg²⁺. Results are compared with previous results in the literature and in relation to the branchial morphology and ionic exchanges in fish.     

Effects of varying levels of aqueous potassium and magnesium on survival,growth, and respiration of the Pacific white shrimp,Litopenaeus vannamei,reared in low salinity waters

Inland shrimp culture is being practiced in several regions of the United States. In Alabama, the culture of shrimp (Litopenaeus vannamei) in inland low salinity well water (approximately 4.0 ppt) faces several challenges. The ionic composition of these waters is deficient in several key minerals, including potassium (K⁺) and magnesium (Mg²⁺). The objective of the present study was to evaluate the effects of several aqueous K⁺ and Mg²⁺ concentrations on survival, growth, and respiration in juvenile L. vannamei. Two experiments, a 14-day trial with postlarvae and a 7-week trial with juvenile (∼ 0.2 g) shrimp were conducted to evaluate effects of K⁺ supplementation to culture water. Four different levels of K⁺ (5, 10, 20, and 40 mg l^− 1) were utilized and a treatment of 4 ppt reconstituted seawater was used as a reference for comparison to ideal ionic ratios. Additionally, a 6-week growth trial (∼ 1 g juvenile shrimp) was performed to evaluate the effects of five concentrations of Mg²⁺ (10, 20, 40, 80, 160 mg l^− 1). Following completion of growth trials, measurements of basal respirometry rates were conducted to assess stress. Results from the 7-week K⁺ growth trial indicated significant differences (P < 0.05) in survival and growth among treatments. Individual weight, specific growth rate, and percent weight gain appeared to increase with increasing K⁺ concentration (decreasing Na:K ratios). Results from the Mg²⁺ experiment reveal a significant difference in survival between the lowest Mg²⁺ treatment (60%) and all other experimental treatments (90–97%). However, no differences in growth were observed. Shrimp respiration in the lowest Mg²⁺ treatment (10 mg l^− 1) was significantly higher than in the 80 mg l^− 1 treatment. These results suggest a potentially higher energetic cost associated with depressed aqueous Mg²⁺ concentrations that are common in low salinity environments.     

Sperm motility and fertilizing ability in the Persian sturgeon Acipenser persicus

The motility and fertilizing ability of the Persian sturgeon, Acipenser persicus, spermatozoa were investigated. Optimum ionic content (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and pH of activation solution as well as the optimum dilution rate were determined. The results show optimum motility characteristics of spermatozoa in buffered solutions containing 25, 0.2, 3 and 10 mM L^?1 Na⁺, K⁺, Ca²⁺ and Mg²⁺, respectively, at dilution rate 1:50 and pH 8.0. To test the fertilizing ability of sperm, two buffered saline solutions were used as activation solution of sperm motility. The present study indicated (1) spermatozoa motility is one of key factors that influence on fertilizing ability of sperm, (2) a high fertilizing ability of sperm is obtained after dilution in saline solutions rather than in freshwater and (3) a maximum fertilization rate occurs in buffered saline solution containing 0.2 mM L^?1 K⁺. There is also a good correlation between biochemical characteristics of seminal plasma and fertilizing ability of sperm.     

Diet supplemented with probiotic for Nile tilapia in polyculture system with marine shrimp

The aim of this study was to assess the effect of a probiotic (Lactobacillus plantarum) supplemented diet on Nile tilapia (Oreochromis niloticus) in a polyculture system with marine shrimp (Litopenaeus vannamei) as regards culture performance, hematology, and gut bacterial microbiota. Ten 20-m2 pens were arranged in one earthen pond and stocked with 2 fish (41.9 g) m⁻² and 10 shrimp (2.3 g) m⁻², in total of 40 Nile tilapias and 200 shrimp per experimental unit. Tilapia groups in five of the experimental units were fed a commercial diet supplemented with L. plantarum and the other five with an unsupplemented commercial diet (control). After 12 weeks of culture, the tilapia groups fed the probiotic-supplemented diet presented values 13.6, 7.5, and 7.1% higher for feed efficiency, yield, and final weight, respectively. Viable culturable heterotrophic bacteria counts were reduced, and the number of lactic acid bacteria was increased in the gut of fish and shrimp fed the probiotic-supplemented diet. Hematological analyses showed higher number of thrombocytes and leukocytes in tilapia fed the supplemented diet. L. plantarum utilized in this study colonized the gut of tilapia and shrimp and resulted in reduced number of total bacteria and increased tilapia final weight and feed efficiency.     

Effects of Na/K and Mg/Ca ratios in saline groundwaters on Na-K-ATPase activity, survival and growth of Marsupenaeus japonicus postlarvae

The effects of the Na⁺/K⁺ and Mg²⁺/Ca²⁺ ratios in saline groundwaters on Na⁺-K⁺-ATPase activity, survival and growth of Marsupenaeus japonicus postlarvae were investigated. The results indicate that the Na⁺-K⁺-ATPase activity, survival rate and weight gain of postlarvae were significantly affected by the Na⁺/K⁺ and Mg²⁺/Ca²⁺ ratios (P < 0.05). The Na⁺-K⁺-ATPase activity of postlarvae, in every treatment, changed corresponding to Na⁺/K⁺ and Mg²⁺/Ca²⁺ ratios, and came to a stable level after 24 h. There was a negative relation between Na⁺-K⁺-ATPase activity and Na⁺/K⁺ ratio, while there was a positive relation between Na⁺-K⁺-ATPase activity and Mg²⁺/Ca²⁺ ratio. Compared with seawater (the Na⁺/K⁺ and Mg²⁺/Ca²⁺ ratios are 27.8 and 4.64 respectively), the Na⁺-K⁺-ATPase activity of the Na⁺/K⁺ ratio 30 treatment showed no significant difference, while the Mg²⁺/Ca²⁺ ratio 4.5 treatment showed distinct difference. The survival rates and weight gain of postlarvae increased markedly when the suitable amount of K⁺ and Ca²⁺ was added to test water, and arrived at their maximum in the Na⁺/K⁺ ratio 20-30 or Mg²⁺/Ca²⁺ ratio 4.5 treatment, having no significant difference compared with normal seawater. Therefore, considering the Na⁺/K⁺, Mg²⁺/Ca²⁺ ratios and the absolute concentration of Mg²⁺, Ca²⁺ in the experimental saline groundwaters applied to Marsupenaeus japonicus farming, it should be modulated to around 30, 4.5 and 1312 mg/l, 291 mg/l, respectively.     

Effects of dietary chitosan on growth,survival and stress tolerance of postlarval shrimp,Litopenaeus vannamei

The effect of chitosan, a polymer of glucosamine obtained by the deacetylation of chitin, on growth, survival and stress tolerance was studied in postlarval Litopenaeus vannamei. An experiment was performed with postlarval shrimp (mean initial wet weight 1.2 mg) fed five isoenergic and isonitrogenous diets containing five supplemented levels of chitosan (0, 0.5, 1, 2 and 4 g kg^?1 diet, respectively). The five compound diets (C0, C0.5, C1, C2 and C4) sustained shrimp growth throughout the experiment. Growth performance (final body weights; weight gain; SGR: specific growth rate) in shrimp fed diet C2 was significantly higher than that in shrimp fed diets C0, C0.5 and C1 (P < 0.05), diet C4 treatment provided intermediate growth result. The survival in shrimp fed diet C1 was significantly higher than that in shrimp fed C0 diet (P < 0.05), other diets treatments gave the intermediate survival results. No significant differences were found in growth and survival between diet C2 and C4 treatments. After 9 days of a stress tolerance test, survival in shrimp fed diets C1, C2 and C4 was significantly higher than that in shrimp fed diets C0 and C0.5. We concluded from this experiment that the incorporation of a moderate dietary chitosan was beneficial to the development of postlarval L. vannamei. Considering the effect of chitosan on both growth and survival of postlarval L. vannamei, second‐degree polynomial regression of SGR and survival indicated optimum supplement of dietary chitosan at 2.67 and 2.13 g kg^?1, respectively, so the level of chitosan supplemented in the diet should be between 2.13 and 2.67 g kg^?1.     

Dietary magnesium requirement and physiological responses of marine shrimp Litopenaeus vannamei reared in low salinity water

An 8‐week feeding experiment was conducted to determine the dietary magnesium (Mg) requirement and physiological responses of Litopenaeus vannamei in low salinity water of 2 g L^?1. Casein–gelatin‐based diets supplemented with seven levels of Mg (0, 0.4, 0.8, 1.6, 3.2, 6.4 and 8.0 g kg^?1) were fed to juvenile shrimp. Prior to the experiment, the postlarvae were gradually acclimated to the low salinity media and fed with a basal diet (0.5 g Mg kg^?1) for 2 weeks. After 8 weeks of feeding, survival ranged from 80.11% to 85.65% with no significant difference among the treatments. Hepatopancreas Mg²⁺‐ATPase and Na⁺/K⁺‐ATPase activities and muscle content of lipid and protein were not significantly affected by graded levels of Mg. The weight gain and mineral (calcium, potassium, sodium and total phosphorus) content of different tissues were significantly affected by dietary Mg levels, while there were no significant differences in ash and zinc content in tissues. The Mg content in tissues except hepatopancreas was maintained relatively constant regardless of dietary treatments. The dietary Mg requirement for optimal growth was 2.60–3.46 g Mg kg^?1 by using the polynomial regression analysis based on growth.     

Response of ATPases in the osmoregulatory tissues of freshwater fish Oreochromis niloticus exposed to copper in increased salinity

An increase in salinity of freshwater can affect the physiology and metal uptake in fish. In the present study, Nile tilapia Oreochromis niloticus were exposed to copper (1.0 mg/l) in increased salinities (2, 4, and 8 ppt) for 0, 1, 3, 7, and 14 days. Following the exposures, the activities of Na⁺/K⁺-ATPase, Mg²⁺-ATPase, and Ca²⁺-ATPase were measured in the gill, kidney, and intestine to evaluate the changes in osmoregulation of fish. Results showed that increases in salinity and Cu exposure of fish significantly altered the ATPase activities depending on the tissue type, salinity increase, and exposure durations. Salinity-alone exposures increased Na⁺/K⁺-ATPase activity and decreased Ca²⁺-ATPase activity. Na⁺/K⁺-ATPase activity decreased following Cu exposure in 2 and 4 ppt salinities, though the activity increased in 8 ppt salinity. Ca²⁺-ATPase activity decreased in the gill and intestine in all salinities, while the activity mostly increased in the kidney. However, there were great variations in Mg²⁺-ATPase activity following exposure to salinity alone and salinity+Cu combination. Cu accumulated in the gill and intestine following 14 days exposure and accumulation was negatively correlated with salinity increase. Data indicated that ATPases were highly sensitive to increases in salinity and Cu and might be a useful biomarker in ecotoxicological studies. However, data from salinity increased freshwaters should carefully be handled to see a clear picture on the effects of metals, as salinity affects both metal speciation and fish osmoregulation.     

The effects of different Ca2+ concentration fluctuation on the moulting,growth and energy budget of juvenile Litopenaeus vannamei (Boone)

A 40‐day experiment was conducted to investigate the effects of different Ca²⁺ concentration fluctuation on the moulting, growth and energy budget of juvenile Litopenaeus vannamei with an initial wet body weight of (1.20±0.01) g. The Ca²⁺ concentration of the control group C385 was 385 mg L^?1 throughout the experiment, while the Ca²⁺ concentration of the C591, C803, C1155 and C2380 groups periodically fluctuated from 385 to 591, 803, 1155 and 2380 mg L^?1 respectively. The moulting frequency (MF) of the shrimp in the Ca²⁺ concentration fluctuating groups was significantly higher than those in the control group (P<0.05). The specific growth rates (SGR_d) and feed intake of the shrimp in the C591 and C803 groups were significantly higher than those in other groups (P<0.05), but no significant differences in feed efficiency were found among all groups (P>0.05). The shrimp in C591 and C803 groups spent significantly less energy in respiration, while depositing significantly more energy for growth than those in other three groups (P<0.05). These results showed that proper Ca²⁺ concentration fluctuation could increase the MF and growth rate of the juvenile L. vannamei, and according to the regression formula made using SGR_d and range of Ca²⁺ concentration fluctuation, periodically enhanced Ca²⁺ concentration of 295 mg L^?1 in the seawater was suggested to be used in shrimp culture.     

Influence of dietary phospholipids level on growth performance,body composition and lipid class of early postlarval Litopenaeus vannamei

One experiment was conducted to determine the nutritive value of phospholipids on growth performance of early postlarval shrimp, Litopenaeus vannamei. Five isoenergic and isonitrogenous diets with five supplemented levels of phospholipids (P1, P2, P3, P4 and P5 with 0, 10, 20, 40 and 80 g kg^?1 diet, respectively) were fed to triplicate groups of L. vannamei (mean initial wet weight 0.8 mg) for 27 days. After the 27‐day feeding trial, the lowest weight gain (WG, %) and specific growth rate (SGR, % day^?1) was found in P1 treatment, the highest WG and SGR was found in P3, P4 and P5 treatments, P2 treatment provided intermediate result and showed significant difference compared to P1, P3, P4 and P5 treatments. Shrimp fed the P1 diet had significantly lower survival than shrimp fed other diets, while no significant difference was found in survival among P2, P3, P4 and P5 treatments. Broken‐line analysis on WG indicated that the optimum dietary phospholipids for early postlarval shrimp, L. vannamei, is 45.96 g kg^?1 diet.     

A diet of fructose‐enriched Artemia improves the response of juvenile Litopenaeus vannamei shrimp to acute low‐salinity challenge

The Pacific white shrimp (Litopenaeus vannamei), as an economically important species, has been reared in low‐salinity water during the last decade. To investigate how juvenile L. vannamei shrimp fed with fructose‐enriched Artemia respond to acute low‐salinity stress, the shrimp were randomly divided into four treatment groups, three groups were fed with Artemia enriched with either 100, 200 and 300 mg L^?1 of fructose and a control group fed with Artemia with no enrichment for 10 days. The results showed that the 300 mg L^?1 fructose group demonstrated the maximum survival rate and glycogen content. Additionally, the 300 mg L^?1 fructose group showed significantly higher Na⁺/K⁺‐ATPase activity, total antioxidant capacity, and expression levels of Na⁺/K⁺‐ATPase α‐subunit, V‐H ATPase α‐subunit, hexokinase, phosphofructokinase, antioxidants (SOD, CAT, GPX) and Hsp70 mRNA when compared with the control group. Furthermore, after exposure to low salinity, the mRNA levels of phosphofructokinase, V‐H ATPase α‐subunit, GPX, p38, JNK and Rac1 stayed constant in shrimp fed with fructose‐enriched Artemia but changed significantly in the control group. Thus, a diet of fructose‐enriched Artemia can improve the osmoregulation and survival of juvenile L. vannamei shrimp exposed to low salinities.     

The effect of postprandial changes in pH along the gastrointestinal tract on the distribution of ions between the solid and fluid phases of chyme in rainbow trout

An area of emerging importance is the role that the diet can play in alleviating the demands for ion uptake in fish living in a freshwater environment, by providing a highly concentrated supply of electrolytes. The availability of ions for uptake from the diet likely requires dissolution in the fluid phase of the chyme. However, the distribution of ions between the fluid and solid phases of chyme has not been well‐characterized in fish, and little is known about the effects of location along the gastrointestinal (GI) tract, or about the pH gradients found therein, on this distribution. Hence, the pH and ionic concentrations (Na⁺, K⁺, Cl^?, Ca²⁺ and Mg²⁺, in both fluid and solid phases) of the chyme in each GI tract section were measured at various time points during the digestion of a single meal of commercial pellets in freshwater rainbow trout (Oncorhynchus mykiss). Additionally, the presence of an inert reference marker (lead‐glass beads) in the diet was used to quantify the distribution of these ions between the solid and fluid phases of the chyme. The buffering capacity of the food was evident in the acidic stomach (ST), whereas the intestine provided an alkaline environment for further digestion. It appeared that pH had little influence on the distribution of the monovalent ions between the phases in all GI tract sections. However, the ST showed significant changes in the partitioning of both Ca²⁺ and Mg²⁺, with each mineral becoming highly dissolved as the gastric chyme pH decreased. This was followed by subsequent precipitation of both minerals in the alkaline environment of the intestine. The high degree of dissolution of Ca²⁺ and Mg²⁺ in the fluid phase of gastric chyme corresponded with large absorptive rates from the ST seen previously, however, this was not true of the monovalent ions.     

Some Limiting Factors in Superintensive Production of Juvenile Pacific White Shrimp,Litopenaeus vannamei,in No‐water‐exchange,Biofloc‐dominated Systems

Superintensive shrimp culture in zero‐exchange, biofloc‐dominated production systems is more biosecure and sustainable than traditional shrimp farming practices. However, successful application of this technology depends upon optimizing dietary formulations, controlling Vibrio outbreaks, and managing accumulative changes in water quality and composition. A 49‐d study investigated the effect of two commercial feeds of differing protein content and an indoor limited‐exchange, biofloc‐dominated culture environment on Litopenaeus vannamei performance and tissue composition, water quality and ionic composition, and Vibrio dynamics. Juveniles (5.3 g) were stocked at 457/m³ into four 40 m³ shallow raceways containing biofloc‐dominated water and fed one of two commercial feeds with differing protein content, 35 or 40%. Shrimp performance, Vibrio populations, and changes in shrimp and culture water composition were monitored. There were no significant differences (P > 0.05) in shrimp performance (survival, weight, growth, specific growth rate, total biomass, yield, feed conversion ratio, and protein efficiency ratio) or proximate composition between feed types. The 40% protein feed resulted in higher culture water nitrate and phosphate concentrations, alkalinity consumption and bicarbonate use, and higher phytoplankton density. The presence of Vibrio, specifically Vibrio parahaemolyticus, reduced shrimp survival. This survival decrease corresponded with increased culture water Vibrio concentrations. Culture water K⁺ and Mg²⁺ increased significantly (P < 0.05), and Sr²⁺, Br^?, and Cl^? decreased significantly (P < 0.05) over time. While Cu²⁺ and Zn²⁺ did increase in shrimp tissue, no heavy metals accumulated to problematic levels in culture water or shrimp tissue. These results demonstrate the importance of monitoring Vibrio populations and ionic composition in limited‐exchange shrimp culture systems.     

凡纳滨对虾C型凝集素（LvLc1）的特征和活性分析

C型凝集素是一种依赖于Ca~(2+)而发挥功能的糖蛋白,在一线的固有免疫防御过程中发挥着重要作用。围绕对虾C型凝集素开展深入研究,不仅可以丰富无脊椎动物固有免疫学内容,还有望将其开发为具有免疫增强效果的活性饵料,应用于对虾的健康养殖。本实验根据实验室前期转录组信息提示克隆获得了凡纳滨对虾一种新的C型凝集素基因(LvLc1,Gen Bank注册号:KY937940)。生物信息学分析显示LvLc1基因的开放阅读框全长891 bp,编码296个氨基酸,该基因编码的蛋白质含有一个保守的糖识别结构域(carbohydrate recognition domain,CRD),该结构域中具有潜在的半乳糖结合位点(QPD motif),进化发生分析显示LvLc1与来自节肢动物的甘露糖结合凝集素家族成员聚类在一起。对LvLc1基因的CRD结构域进行了原核重组表达与蛋白活性分析研究,结果显示:重组目的蛋白(rLvLc1)在Ca~(2+)存在的条件下,对多种病原菌(G~+、G~–和真菌)具有凝集作用,其凝集活性可被半乳糖、甘露糖、脂多糖等多种病原相关分子模式所抑制。研究表明,LvLc1作为C-型凝集素家族一个新成员,可能通过重要的模式识别受体作用,参与机体应答病原微生物侵染的防御过程。     

Ca2+- and Mg2+-Induced Conformational and Rheological Changes of Actomyosin Extracted from Fresh and Freeze-Thaw Tilapia

ABSTRACT

The conformational changes of natural actomyosins prepared from fresh and freeze-thaw tilapia (Oreochromis niloticus) in the presence of Ca²⁺ or Mg²⁺ were investigated. The Ca²⁺-activated adenosine triphosphatase (Ca²⁺-ATPase) activities of actomyosins extracted from fresh and freeze-thaw fish were comparable (p > 0.05). The denaturation temperatures (T_d) of actomyosins extracted from fresh fish were lower than those from freeze-thaw counterparts (p < 0.05). The addition of Ca²⁺ or Mg²⁺ reduced the T_d of actomyosins. Ca²⁺ and Mg²⁺ enhanced protein aggregation at ≥ 40°C (p < 0.05). Based on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern, the myosin heavy chain (MHC) and actin bands tended to form large aggregates to a greater extent in the presence of 100mM Ca²⁺ or Mg²⁺. Ca²⁺ and Mg²⁺enhanced disulfide linkages and hydrophobic interactions among actomyosin molecules. The onset temperature of elastic modulus (G′) of both actomyosins was shifted to lower temperature as 100mM of Ca²⁺ or Mg²⁺ was added. Mg²⁺ at 20mM increased the breaking force of washed tilapia mince at 40°C. Our results revealed that the intrinsic properties of actomyosins extracted from fresh and frozen fish were distinct, and divalent ions Ca²⁺ or Mg²⁺ affected their gelation differently.     

Arginine effects on biochemical composition of sperm in rainbow trout,Oncorhynchus mykiss

The present study investigated the effect of arginine on seminal plasma composition in rainbow trout. Male rainbow trout broodstocks (2500 ± 200 g) were fed five practical diets (each consisting of three triplicates) supplemented with Arginine at 0.50%, 1.50% and 2.00%. The control group were fed without arginine. Broodstock feeding lasted for 90 days, and then fish semen was sampled. Results indicated no significant differences in LDH, ALP, Fe²⁺ and phosphorous content among the different treatments. The lowest levels of AST and ALT and the highest levels of Ca²⁺ and Mg²⁺ ions were observed in the treatment fed with 1.50% arginine, which showed significant differences from other treatments (P < 0.05). Moreover, the amount of Cl^?, Na⁺ and K⁺ ions was significantly increased in the seminal plasma in fish fed diets containing arginine in comparison with the control. As the amount of arginine was increased, the levels of uric acid became significantly greater in contrast to urea and glucose levels. The highest amounts of cholesterol, fructose and total protein were observed in treatments fed on 2.00%, 0.50% and 1.00% arginine, respectively, showing significant differences from other treatments (P < 0.05). The highest pH value was assayed in the 1.50% arginine treatment. Results indicated that arginine had a potential efficacy on semen quality in rainbow trout broodstocks.