Juvenile Litopenaeus Vannamei Research Articles

Litopenaeus vannamei juveniles energetic balance and immunological response to dietary protein

The present study was designed to evaluate the effect of dietary protein level on survival, assimilation efficiency and immunological condition of Litopenaeus vannamei juveniles using two protein levels in a range of optimal reported levels of 15% and 40% (equivalent to 15 and 40 g DP/kg body weight/day [g DP/kg BWd]) and one extremely low (5% equivalent to 5 g DP/kg BWd). In order to reach this goal, effects of dietary protein level on energetic balance were recorded by ingestion rate ( I), respiratory rate ( R) and biomass production of L. vannamei during its growing process ( P). Energy lost from feces ( H) and urine products ( U) was calculated as ( H+ U)= I− R+ P and assimilated energy (As) as R+ P. At the end of the growth experiment, shrimp immune response, oxyhemocyanin (OxyHc), osmotic pressure and digestive gland glycogen were measured. Dietary protein level enhanced ingestion rate in shrimp fed 5 g DP/kg BWd compared to shrimp fed 40 g DP/kg BWd. However, daily growth coefficient (DGC, %)of L. vannamei juveniles was high in shrimp fed 40 g DP/kg BWd in comparison to shrimp fed 5 g DP/kg BWd. An inverse relation between wastes ( H+ U) and dietary protein level was observed indicating that shrimp loose 81% of ingested energy when fed 5 g DP/kg BWd and only 5.6% when fed 40 g DP/kg BWd. A higher assimilation and production efficiency ( P/As) was obtained when shrimp were fed 40 g DP/kg BWd, than obtained in shrimp fed 15 or 5 g DP/kg BWd and an inverse relation between R and respiratory efficiency ( R/As) in relation to dietary protein levels was also observed. An increase in OxyHc was observed with increasing dietary protein levels indicating that shrimp accumulated protein as hemocyanin. A reduction of hemocytes occurred when shrimp were fed sub-optimal dietary protein levels indicating that zymogens contained in hemocytes, i.e., prophenoloxidase (ProPO) system, peneidins and their activities (phagocytosis, coagulation), were also reduced. A reduction on respiratory burst was observed indicating that sub-optimal dietary protein level affected the number of cells and the phagocytosis capacity of cells. Notwithstanding, the compensatory mechanism used by L. vannamei to respond nutritional stress, sub-optimal dietary protein level (5 and 15 g DP/kg BWd) induced not only a severe reduction in growth rate and assimilation efficiency but also in immune capacities.

Effects of Na/K ratio in seawater on growth and energy budget of juvenile Litopenaeus vannamei

The effects of seawater Na/K ratio on growth and energy budget of juvenile Litopenaeus vannamei Boone, 1931 were investigated. Salinity (S=30 ppt) and the total concentration of sodium and potassium in the experimental water were kept constant. Seven treatments were set: R1, R2, R3c, R4, R5, R6 and R7, the Na/K ratios were 25.6, 34.1, 47.3, 85.2, 119.3, 153.3 and 187.4 (mmol/mmol), respectively. The shrimp in R7 (Na/K=187.4) died within 2 weeks after the experiment began. After the 30-day feeding trial, the molting frequency (MF) and feed intake in terms of wet weight (FIw) and energy content (FIe) of the shrimp under the other six treatments were not significantly affected by the different Na/K ratios in the seawater. The final wet weight, weight gain (WG), specific growth rates (SGRw and SGRe) and food conversion efficiencies (FCEd and FCEe) of the shrimp under Treatment R6 were significantly lower than those under the other five treatments. There was a trend that, with all the indices mentioned above, the values of the test shrimp under Treatment R2 was the highest, and the sequence was: R2 (Na/K=34.1)>R3c (Na/K=47.3)>R1 (Na/K=25.6)>R4 (Na/K=85.2)>R5 (Na/K=119.3)>R6 (Na/K=153.3). In the experiment, the percentages of energy deposited for growth (G), energy lost for respiration (R), energy lost in excretion (U) and energy lost in exuviae (E) to the energy consumed in food (C) were significantly affected by the different Na/K ratios in seawater, while the percentage of energy lost in feces (F) to C was not significantly affected by the ratios. The percentage of G to C of the test shrimp under Treatment R6 was significantly lower while the percentage of E to C was significantly higher than those under the other treatments. There were no significant differences among the energy allocations of the test shrimp under Treatment R1, R2, R3c, R4 and R5. According to regression analysis, optimal shrimp growth could be obtained by regulating the Na/K ratio of the seawater to 40–43 at a salinity of 30 ppt.

Development of monoclonal antibodies for detection of necrotizing hepatopancreatitis in penaeid shrimp

Monoclonal antibodies (MAbs) were produced against necrotizing hepatopancreatitis bacteria (NHP-B) of penaeid shrimp. The MAbs tested in dot-immunoblot (D-IB) assays were capable of detecting the NHP-B in hepatopancreas samples collected from moribund juvenile Litopenaeus vannamei during an experimentally induced NHP-B infection. The MAbs were also screened by immunohistochemistry (IHC) using case submissions that were determined to be infected not only by histology, but also polymerase chain reaction (PCR) and in situ hybridization (ISH) assays using specific digoxigenin (DIG)-labeled probes on histological sections prepared from naturally infected shrimp. Two of the MAbs were chosen for development of detection methods for NHP. The MAbs were tested using IHC methods on Davidson's alcohol-formalin-acetic acid (AFA) fixed tissue sections and identified NHP-B infected cells and tissues in a pattern similar to that seen with DIG-labeled NHP-specific gene probes. None of the MAbs reacted with tissue from specific pathogen-free (SPF) shrimp or with shrimp tissues infected with a rickettsia-like bacteria, Vibrio sp., Campylobacter sp., and Spiroplasma sp. The MAbs were found to be negative against these other organisms, demonstrating that they are species specific and useful for rapid diagnostic detection of NHP-B.

Substitution of fish meal by co-extruded soybean poultry by-product meal in practical diets for the Pacific white shrimp, Litopenaeus vannamei

The use of a co-extruded soybean poultry by-product meal with egg supplement was evaluated as a substitute for fish meal in a practical diet formulated to contain 32% crude protein and 8% lipid. The co-extruded product was substituted for menhaden fish meal on an iso-nitrogenous basis and offered to juvenile Litopenaeus vannamei (mean initial weight±standard deviation, 1.13±0.06 g) over a 6-week period. Inclusion levels ranged from 0% (30 g fish meal/100 g diet) to 100% replacement (0 g fish meal/100 g diet). A fifth diet was formulated to contain no fish meal and 1 g krill meal/100 g diet. Furthermore, a commercial shrimp feed was included in the study to allow for a commercial reference. At the conclusion of the growth trial, survival, final weight, percent weight gain and feed efficiency (FE) were not significantly different among treatments. The inclusion of krill meal did not appear to improve attractability or palatability of the diet. Co-extruded soybean poultry by-product meal with egg supplement appears suitable as a substitute for fish meal in L. vannamei diets.

Effect of Dietary Phospholipids on the Choline Requirement ofLitopenaeus vannamei Juveniles

AbstractAn 8‐wk feeding trial was conducted with a 3 ± 4 factorial design for evaluating the nutritional relationship between phospholipids (lecithin at 0, 1.5% or 3% of diet) and choline chloride (0, 1,000, 2,000, or 4,000 mg/kg diet) in juvenile Litopenaeus vannamei. In addition, diets with five graded levels of choline chloride (0, 500, 1,000, 2,000, and 4,000 mg/kg) without supplemental phospholipids or cholesterol were fed for determining the dietary choline requirement. Overall survival was 99% with no difference among the dietary treatments. The choline requirement was estimated to be 871 mg/kg diet without dietary phospholipids. No choline requirement was evident when lecithin was provided at 1.5% and 3% of diet. Shrimp growth significantly increased with incremental dietary phospholipids regardless of choline chloride level. These results indicate that lecithin could effectively provide choline. Conversely, synthesis of phospholipids from choline could not meet the phospholipids requirement of shrimp. Both dietary lecithin and choline chloride supplementation reduced lipid in shrimp muscle. However, only lecithin supplementation increased lipid in hepatopancreas, and dietary choline chloride decreased the level of other phospholipids (except phosphatidylcholine) in shrimp muscle.

Acute toxicity of nitrite on Litopenaeus vannamei (Boone) juveniles at different salinity levels

Litopenaeus vannamei juveniles (total length 56±9.6 mm) were exposed to different concentrations of nitrite-N (nitrite as nitrogen), using a static renewal method at salinity levels of 15‰, 25‰ and 35‰ (g/kg) pH 8.02 and 18 °C. The 24-, 48-, 72-, 96- and 144-h LC50 value of nitrite-N on L. vannamei juveniles were 187.9, 142.2, 92.5, 76.5, 61.1 mg/l at 15‰; 274,1, 244.0, 224.8, 178.3, 152.4 mg/l at 25‰; 521.2, 423.9, 375.0, 321.7, 257.2 mg/l at 35‰, respectively. As the salinity decreased from 35‰ to 15‰, susceptibility of nitrite-N increased by 277%, 298%, 405% and 421% after 24-, 48-, 72-, 96- and 144-h exposure, respectively. The “safe level” for rearing L. vannamei juveniles was estimated to be 6.1, 15.2, 25.7 mg/l for nitrite-N in 15‰, 25‰ and 35‰, respectively. The relationship between LC50 of nitrite-N (mg/l), salinity (S) and exposure time (T) is as follows: LC50=123.0182+0.3657S−0.6072T (R2=0.9847).

Physiological, nutritional, and immunological role of dietary β 1-3 glucan and ascorbic acid 2-monophosphate in Litopenaeus vannamei juveniles

Abstract The present study was designed to determine the effect of dietary β 1-3 glucan (BG) and a megadose of vitamin C on the nutrition (growth and survival, blood glucose, lactate, acylglycerides, cholesterol, hemocyanin [Hc], digestive gland glycogen [DGG]) and the immunological system (blood cells, prophenoloxidase [ProPO]) in Litopenaeus vannamei juveniles. Each treatment was replicated five times. Nutritional condition and immunological response of shrimp were recorded after 40 days of feeding with specific diets and during 48 h after a salinity shock (35–0‰). A significantly greater growth rate was observed in shrimp fed with BG or vitamin C diets than in the control group. Higher blood protein, total blood cells, granular cells, and ProPO activity were recorded in shrimp fed with vitamin C as compared to the remaining treatments. That means that BG was degraded in the digestive gland by β-glucanases to produce energy, permitting the use of more proteins for growth, whereas vitamin C was used to improve animal health, enhancing general metabolism in shrimp. The salinity stress induced a rapid use of reserves, triacylglycerols (TAGs), and cholesterol were reduced in blood and probably used as a source of energy or synthesis in the digestive gland. The increase in digestive gland glycogen 24 h after the salinity shock evidenced the use of these reserves by shrimp fed with all diets. In general, after the salinity, shock blood cells increased in shrimp fed with glucans and decreased in shrimp fed with vitamin C, whereas ProPO decreased in all shrimp after the salinity shock. This could mean that after the salinity, shock shrimp fed with glucans could synthesize cells and ProPO, whereas in shrimp fed with vitamin C, blood cells were just used to respond to the stress. After the salinity shock, an increment in the ProPO/granular cell ratio was observed in shrimp fed with vitamin C, indicating that these shrimp could rapidly increase the components of their immune system. In contrast, a continuous reduction in ProPO/granular cell ratio was observed in shrimp fed with glucans, revealing that with this type of immunostimulant, shrimp drive their immunological equipment to respond continuously to the stress. These results could explain why shrimp fed with immunostimulants presents immunological fatigue in contrast to shrimp fed with additives that improve their nutritional status, like vitamin C.

Nutritional evaluation of fatty acids for the open thelycum shrimp, Litopenaeus vannamei : II. Effect of dietary n-3 and n-6 polyunsaturated and highly unsaturated fatty acids on juvenile shrimp growth, survival, and fatty acid composition

This study evaluated the nutritional value of dietary n-3 and n-6 polyunsaturated fatty acids (PUFA) such as linoleic (LOA) and linolenic (LNA) acids, and highly unsaturated fatty acids (HUFA) such as arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids for juvenile Litopenaeus vannamei, based on their effects on growth, survival, and fatty acid composition of hepatopancreas and muscle tissue. Diets contained 5% total lipid. A basal diet contained palmitic and stearic acids each at 2.5% of diet. Five diets contained 0.5% dry weight of LOA, LNA, AA, EPA, or DHA. An additional diet evaluated HUFA in combination by supplementing at 0.5% of diet, a mixture of n-3 HUFA. All HUFA showed higher nutritional value than PUFA for shrimp and produced significantly (P < 0.05) higher final weight, weight gain, and total lipid in shrimp muscle. Fatty acid profiles of shrimp tissues reflected the composition of the dietary lipids. In general, saturated fatty acids were more abundant in the neutral factions, while PUFA and HUFA were more abundant in the polar fractions of tissues. Under these experimental conditions, HUFA had much greater nutritional value than PUFA for juvenile L. vannamei; moreover, dietary requirements for PUFA were not demonstrated.

Nutritional evaluation of fatty acids for the open thelycum shrimp,Litopenaeus vannamei: I. Effect of dietary linoleic and linolenic acids at different concentrations and ratios on juvenile shrimp growth, survival and fatty acid composition

A 6-week feeding trial was conducted to evaluate the nutritional value of dietary linoleic (18:2n-6, LOA) and linolenic (18:3n-3, LNA) acids for juvenile Litopenaeus vannamei by determining their effects on growth, survival and fatty acid composition of hepatopancreas and muscle tissue. Diets were formulated to contain 5% total lipid. A basal diet contained only palmitic and stearic acids, each at 2.5% of diet. Six diets contained one of three levels (0.25, 0.5 and 1%) of either LOA or LNA, and three diets had different ratios of LNA/LOA (1, 3, 9) at a combined inclusion level of 0.5% of diet. An additional diet contained 0.5% of a mixture of n-3 highly unsaturated fatty acids (HUFA). The fatty acid profile of hepatopancreas and muscle of shrimp reflected the profile of the diets. HUFA of the n-3 family showed higher nutritional value than LOA or LNA for juvenile L. vannamei by producing significantly (P < 0.05) higher final weight and weight gain. Neither LOA nor LNA, alone or in combination, improved growth significantly compared with shrimp fed the basal diet.Thus, dietary requirements for LOA and LNA were not demonstrated under these experimental conditions.

Biological Characterization of a Less Virulent Taura Syndrome in Pacific White Shrimp Litopenaeus vannamei (Crustacea: Decapoda): Gross Signs, Histopathological Lesions, and Mortalities

Taura syndrome (TS) was first recognized in shrimp farms located near the mouth of the Taura River in the Gulf of Guayaquil, Ecuador in mid1992 (JimCnez 1992; Lightner et al. 1995), where the disease caused catastrophic losses with cumulative mortality rates from 60% to >90% of affected pond-cultured, juvenile Pacific white shrimp Litopenaeus vannamei (Perez Farfante and Kensley 1997). The geographic distribution of the disease now includes Ecuador, the adjacent region of Peru, the Pacific and Caribbean coast of Colombia, Honduras, Guatemala, El Salvador, northeast Brazil, Nicaragua, Belize, the states of Hawaii, Florida, and Texas in the USA, the Mexican states of Sonora, Sinaloa, Chiapas, and Guerrero, and recently Taiwan (Lightner 1996; Chien et al. 1999). The epizootiological and laboratory studies that followed its discovery and spread from Ecuador showed that Taura syndrome (TS) had a viral etiology in the American (L. vannamei, L. stylirostris, L. schmitti, L. setiferus, Farfuntepenaeus aztecus) and Asian (Penaeus monodon, Marsupenaeus japonicus, Fenneropenaeus chinensis) penaeid species naturally or experimentally infected by the virus. Litopenaeus vannamei was by far the most severely affected (Brock et al. 1995, 1997; Hasson et al. 1995, 1999b; Lightner 1996; Overstreet et al. 1997). Infectivity studies demonstrated that TS could be induced in specific-pathogen-free (SPF) L. vannamei. Shrimp started dying after being fed TSV-infected tissue between day 4 or 5, with mortalities of 80% (Brock et al. 1995). Test animals were also infected by intramuscular injection with crude homogenate and cell-free suspensions, from TSV-infected Ecuatorian L. vannamei, causing mortalities of 73% to 87% among treated groups. All moribund shrimp demonstrated moderate to severe pathognomonic TS lesions (Hasson et al. 1995), which consist of pyknotic and karyorrhectic nuclei and generally spherical cytoplasmic inclusions with multifocal areas of necrosis of the cuticular epithelium giving TS lesions a peppered or buckshot-riddled appearance (Brock et al. 1995; Lightner et al. 1995; Hasson et al. 1995; Lightner 1999). The hemispheric geographic distribution of TS indicates that the same virus or a closely related one is responsible for the TS epizootics that have occurred throughout America since 1992 (Hasson et al. 1999a). Ecuatorian and Hawaiian TS virus isolates were found to be identical in their biophysical, biochemical, and biological characteristics, and they were considered to be the same virus (Bonami et al. 1997). In early 1995, TSV was detected in wild adult L. vannamei collected from the offshore fishery of the southern Mexican state of Chiapas, near its border with Guatemala and near where TS had first appeared in

Rendered meat and bone meals as ingredients of diets for shrimp Litopenaeus vannamei (Boone, 1931)

The nutritional quality of three sources of rendered meat and bone meals (MBM) was evaluated as feed ingredients in diets for juvenile Litopenaeus vannamei. Two trials were conducted in this work: an in vivo apparent digestibility trial and a growth trial. The apparent digestibility coefficients for dry matter, crude protein and amino acids of diets containing fixed percentages of each protein source were determined using the marker (0.5% chromic oxide) method. A separate feeding trial was conducted to ascertain the maximum level of replacement of high-quality Norwegian fish meal in diets for this species. Nine dry diets were formulated to contain each protein source at 25%, 50% and 75% levels of replacement of fish meal. A 10th diet, the control, contained no meat and bone meal. Fish oil was adjusted to maintain equal lipid levels among the diets. The growth and survival of shrimp fed each diet for 8 weeks were determined. Responses of shrimp to dietary MBMs differed for both the digestibility and the growth trials. The apparent digestibility coefficients of dry matter, protein and amino acids were lower relative to the fish meal for the diets containing the three MBMs, and this difference was statistically significant for two of them. The growth trial, however, revealed that MBM effectively replaced between 25% and 75% of fish meal, depending on which MBM was used. A general decrease in growth above 25% replacement was observed for all MBM sources. The relative rankings of the three MBMs were different based on digestibility and growth performance data, indicating that digestibility itself is insufficient to explain the reduction in growth response relative to dietary fish meal.

Effect of dietary phospholipid on essential fatty acid requirements and tissue lipid composition of Litopenaeus vannamei juveniles

A 6-week study was conducted to evaluate the effect of dietary phospholipids (PL) on essential fatty acid requirements of juvenile Litopenaeus vannamei and their potential interaction. A 3×3 factorial experiment was carried out with increasing levels of soybean lecithin as the dietary PL (0%, 1.5% or 3% of diet). Three dietary levels (0%, 0.25% or 0.5% of diet) of docosahexaenoic acid (22:6 n−3, DHA), or an n−3 highly unsaturated fatty acid (HUFA) mixture containing 416 mg eicosapentaenoic acid (EPA)/g and 237 mg DHA/g were tested. No significant interactions between the effects of PL and DHA or n−3 HUFA on growth were detected under these experimental conditions; however, instantaneous growth rate (IGR) of shrimp was enhanced by addition of either DHA or n−3 HUFA at 0.25% of diet. A higher dietary inclusion level (0.5% of diet) did not further improve growth, and appeared to have a detrimental effect on survival of shrimp. Also, an inclusion level of 3% dietary PL significantly improved IGR of shrimp, and did not show a significant effect on survival. PL supplementation did not consistently increase the proportion of phosphatidylcholine or other PL in shrimp muscle. The proportion of linoleic acid decreased as dietary DHA or n−3 HUFA increased. Thus, these results corroborate the beneficial effects of dietary PL on growth of shrimp, as well as their requirement for DHA and n−3 HUFA to achieve maximum growth.

Growth, survival and fatty acid composition of juvenile Litopenaeus vannamei fed different oils in the presence and absence of phospholipids

A 2×6 factorial study was conducted to evaluate the effect of dietary phospholipids (PL) and different neutral lipids, as well as their potential interaction, on growth, survival and fatty acid composition of hepatopancreas and muscle tissue of juvenile Litopenaeus vannamei. The lipid sources were coconut, soybean, linseed, peanut, and menhaden oils. Five diets contained 5% of each test oil and 3.1% of a commercial lecithin containing 97.6% PL. Five additional diets contained 5% of each oil but no lecithin. A control diet contained 3.1% lecithin but no other oil, and an additional control diet contained no PL but 2.21% soybean oil, 0.41% monobasic sodium phosphate, and 0.48% choline chloride (estimated equivalent of soybean oil, phosphorus and choline in 3.1% lecithin). No significant differences (at P<0.05) among treatments were observed for survival and no significant interactions were observed between the effects of PL and oil type for any of the responses after 8 weeks feeding; however, shrimp fed diets containing PL obtained significantly higher final weight and instantaneous growth rate (IGR), and lower feed conversion ratios (FCR) than those fed diets containing the same oil and no PL. Shrimp fed diets containing menhaden oil, with and without PL, showed higher final weight and IGR, and lower FCR than the rest of the treatments. These diets had a larger variety of fatty acids (FA), especially long chain highly unsaturated FA (HUFA), and showed the highest percentage of arachidonic, eicosapentaenoic and docosahexaenoic acids. Menhaden oil showed a higher nutritional value for juvenile L. vannamei because it provided more essential FA, particularly n−3 HUFA.

Effect of Low Salinity on Growth and Survival of Postlarvae and Juvenile Litopenaeus vannamei

AbstractThe effect of low salinity on survival and growth of the Pacific white shrimp Litopenaeus vannamei was examined in the laboratory due to the interest of raising shrimp inland at low salinities. In three separate experiments, individual L. vannamei postlarvae (∼ 0.1 g) were cultured at salinities of either 0.5, 1, 1.5, 2, or 3 ppt (N= 5 or 10/treatment) for 18 to 40 d at 30 C in individual 360‐mL containers. In each experiment controls of 0 and 30 ppt were run. There was no postlarval survival at salinities &lt; 2 ppt. Survival was significantly different (P &lt; 0.01) at 2 ppt (20%) compared to 30 ppt (80%). Growth was also significantly different (P &lt; 0.01) at 2 and 3 ppt compared to 30 ppt (416%, 475%, and 670%, respectively). A fourth experiment compared juveniles (∼ 8 g) and postlarvae (∼ 0.05 and 0.35 g). Shrimp were cultured at salinities of 0, 2, 4, and 30 ppt for 40 d at 25 C, in individual 360‐mL and 6‐L containers (N= 7/treatment). There was no postlarval survival at &lt; 2 ppt. Postlarval survival at 4 ppt (86%) was not significantly different (P &gt; 0.05) from 30 ppt (100%). Juveniles exhibited better survival at lower salinities (100% at 2 ppt) than 0.05 and 0.35 g postlarvae (29% and 14% respectively, at 2 ppt). The effects of salinity on growth varied with sizdage. Final growth of 0.05 g postlarvae at 2 ppt (693%) was significantly less (P &lt; 0.01) than at 4 ppt (1085%) and 30 ppt (1064%). Growth of 0.35 g postlarvae was significantly less (P &lt; 0.01) for 4 ppt (175%) than for 30 ppt (264%). There was no growth data for juveniles (8 g). It appears from these experiments that the culture of L. vannamei poses risks when performed in salinities less than 2 ppt.

An energetic and conceptual model of the physiological role of dietary carbohydrates and salinity on Litopenaeus vannamei juveniles

We are reporting results directed to explain the relation between carbohydrates (CHO), protein metabolism, and the energetic balance of Litopenaeus vannamei juveniles. The interaction of dietary CHO and salinity was measured to try to understand the relation between osmotic control and metabolism, both from a biochemical and energetic point of view. Two experiments were done. In the first experiment, shrimp were fed with 0%, 5%, 33%, and 61% CHO and maintained at 15‰ and 40‰ salinity. Glucose, lactate protein, hemocyanin, ammonia concentration, and osmotic pressure were measured in blood. Digestive gland glycogen (DGG) was measured also. In the second experiment, shrimp were fed with 0% and 38% dietary CHO and maintained at 15‰ and 40‰ salinity. From that shrimp, absorbed energy (Abs) was calculated as: Abs=respiration ( R)+ammonia excretion ( U) and production ( P); assimilated energy (As) was calculated as the product of R× P. Osmotic pressure, hemocyanin, protein, lactate, and blood ammonia increased with the reduction in dietary CHO. In contrast, an increase in blood glucose was observed with an increase in dietary CHO. Digestive gland glycogen (DGG) increased following a saturation curve with a DGG maximum at 33% dietary CHO. Blood metabolites of fasting and feeding shrimp showed the same behavior. Energy balance results showed that shrimp maintained in low salinity and fed without CHO waste more energy in U production than for shrimp maintained in high salinity and fed with high CHO levels. Notwithstanding, the production efficiency was higher in shrimp fed without CHO than that observed in shrimp fed with high CHO independent of salinity. A scheme trying to integrate the relation between CHO and protein metabolism and the way in which both are modulated by salinity is presented. From published and present results, there are two factors that apparently control the use of high dietary CHO levels; α-amylase enzyme-dietary CHO level capacity and glycogen saturation in DG. Production of glucose is limited in shrimp because of saturation of α-amylase when shrimp are fed with diets above 33% CHO. This is the first control point of starch metabolism. The digestive gland is saturated with glycogen in shrimp fed with dietary CHO levels >33%. This is apparently the second control point of CHO metabolism that limits growth rate in such conditions. The high metabolic cost related to high CHO diets could explain why shrimp are well adapted to use protein as a source of energy.

A dual infection by infectious cuticular epithelial necrosis virus and a Chlamydia -like organism in cultured Litopenaeus vannamei (Boone) in Ecuador

During 1996, microscopic examinations of post larvae and juveniles of moribund Litopenaeus vannamei showed multifocal necrosis in the cuticular epithelial tissues. In addition to these severe degenerative alterations in the epithelial cells typical of infectious cuticular epithelial necrosis virus (ICENV), columnar cells of the epithelium displayed small round intracytoplasmic inclusions in the necrotic tissue. Examination by electron microscopy of affected tissues demonstrated prokaryotic organisms in the cytoplasm of epithelial cells delineated by a distinct cytoplasmic vesicle; the prokaryotic organisms were morphologically similar to the genus Chlamydia. The necrotic tissue also showed the presence of particles of ICENV; the double infection by two different organisms in cuticular epithelial cells has not been reported previously. Two distinct stages in the intracellular development of a Chlamydia-like organism were recognized: (1) pleomorphic elementary bodies (EBs) that were spherical to oval were often observed in the process of division or in forming a common chain of three cells, the cells were surrounded by a rigid cell envelope and the presence of a cap or plaque hexagonally arrayed; (2) the reticular bodies (RBs) were forms often in the process of division. These cells had an electron-dense cytoplasm and contained a loose network of nuclear fibrils and a more fragile cell envelope. Regardless of the development stages of the Chlamydia-like organism within the cytoplasmic vesicles, ICENV particles were observed, either dispersed or in clusters, surrounded or inside the vesicles. The potential adverse impact of this dual infection on shrimp culture should be considered, especially in high-density operations.

Acute toxicity of ammonia on Litopenaeus vannamei Boone juveniles at different salinity levels.

Litopenaeus vannamei juveniles (total length 22+/-2.4 mm) were exposed to different concentrations of ammonia-N (un-ionized plus ionized ammonia as nitrogen), using the static renewal method at different salinity levels of 15 per thousand, 25 per thousand and 35 per thousand at pH 8.05 and 23 degrees C. The 24, 48, 72, 96 h LC50 values of ammonia-N on L. vannamei juveniles were 59.72, 40.58, 32.15, 24.39 mg l(-1) at 15 per thousand; 66.38, 48.83, 43.17, 35.4 mg l(-1) at 25 per thousand; 68.75, 53.84, 44.93, 39.54 mg l(-1) at 35 per thousand, respectively. The 24, 48, 72, 96 h LC50 values of NH(3)-N (un-ionized ammonia as nitrogen) were 2.95, 2.00, 1.59, 1.20 mg l(-1) at 15 per thousand; 2.93, 2.16, 1.91, 1.57 mg l(-1) at 25 per thousand; 2.78, 2.18, 1.82, 1.60 mg l(-1) at 35 per thousand, respectively. As the salinity decreased from 35 per thousand to 15 per thousand, susceptibility of ammonia-N increased by 115%, 132%, 140% and 162% after 24, 48, 72 and 96 h exposure, respectively. The "safety level" for rearing L. vannamei juveniles was estimated to be 2.44, 3.55, 3.95 mg l(-1) for ammonia-N and 0.12, 0.16, 0.16 mg l(-1) for NH(3)-N in 15 per thousand, 25 per thousand and 35 per thousand, respectively.

Metabolism and growth of juveniles of Litopenaeus vannamei: effect of salinity and dietary carbohydrate levels.

The present study was designed to understand how carbohydrate (CBH) and protein metabolism are related in the penaeid shrimp Litopenaeus vannamei. With this information, we obtained a comprehensive schedule of the protein-carbohydrate metabolism including enzymatic, energetic, and functional aspects. We used salinity to determine its role as a modulator of the protein-carbohydrate metabolism in shrimp. Two experiments were designed. The first experiment evaluated the effect of CBH-salinity combinations in growth and survival, and hemolymph glucose, protein, and ammonia levels, digestive gland glycogen, osmotic pressure, and glutamate dehydrogenase (GDH) of L. vannamei juveniles acclimated during 18 days at a salinity of 15 per thousand and 40 per thousand. The second experiment was done to evaluate the effect of dietary CBH level on pre- and postprandial oxygen consumption, ammonia excretion, and the oxygen-nitrogen ratio (O/N) of juvenile L. vannamei in shrimps acclimated at 40 per thousand salinity. We also evaluated the ability of shrimp to carbohydrate adaptation. We made phosphoenolpyruvate carboxykinase (PECPK) and hexokinase activity measurements after a change in dietary carbohydrate levels at different times during 10 days. The growth rate depended on the combination salinity-dietary CBH-protein level. The maximum growth rate was obtained in shrimps maintained at 15 per thousand salinity and with a diet containing low CBH and high protein. The protein in hemolymph is related to the dietary protein levels; high dietary protein levels produced a high protein concentration in hemolymph. This suggests hemolymph is able to store proteins after a salinity acclimation. Depending on the salinity, the hemolymph proteins could be used as a source of osmotic effectors or as metabolic energy. The O/N values obtained show that shrimp used proteins as a source of energy, mainly when shrimps were fed with low CBH. The role played by postprandial nitrogen excretion (PPNE) in apparent heat increase (AHI) (PPNE/AHI ratio) is lower in shrimps fed diets containing high CBH in comparison with shrimps fed diets containing low CBH levels. These results confirm that the metabolism of L. vannamei juveniles is controlled by dietary protein levels, affecting the processes involved in the mechanical and biochemical transformations of ingested food. A growth depression effect was observed in shrimps fed with low-CBH protein diets and maintained in 40 per thousand salinity. In these shrimps, the hemolymph ammonia concentration (HAC) was significantly higher than that observed in shrimps fed with low CBH and maintained in 15 per thousand salinity. That high HAC level coincided with lower growth rate, which suggests that this level might be toxic for juveniles of L. vannamei. Results obtained for GDH activity showed this enzyme regulated both HAC and hemolymph protein levels, with high values in shrimps fed with low CBH levels and maintained in 40 per thousand salinity, and lower in shrimps fed with high CBH and maintained in 15 per thousand salinity. These differences mean that shrimp with a high-gill GDH activity might waste more energy in oxidation of the excess proteins and amino acids, reducing the energy for growth. It was evident that L. vannamei can convert protein to glycogen by a gluconeogenic pathway, which permitted shrimp to maintain a minimum circulating glucose of 0.34 mg/ml in hemolymph. A high PECPK activity was observed in shrimps fed a diet containing low CBH level indicating that the gluconeogenic pathway is activated, as in vertebrates by low dietary CBH levels. After a change in diet, we observed a change in PEPCK; however, it was lower and seems to depend on the way of adaptation, because it occurred after 6 days when adapting to a high-CBH diet and with little change for the low-CBH diet.

Effect of Salinity Acclimation on Oxygen Consumption of Juveniles of the White Shrimp Litopenaeus Vannamei

Effect of Salinity Acclimation on Oxygen Consumption of Juveniles of the White Shrimp Litopenaeus Vannamei

Effects of temperature and salinity on nitrogenous excretion by Litopenaeus vannamei juveniles.

Excretion rates of ammonia-N, nitrite-N, nitrate-N, and dissolved organic nitrogen (DON) for juvenile Litopenaeus vannamei (3.85+/-0.83 g) were quantified in response to nine different combinations of temperature (24, 28, and 32 degrees C) and salinity (10, 25, and 40 ppt) under laboratory conditions. Results indicated that L. vannamei is ammonotelic, with ammonia-N accounting for 61.9-84.3% of total nitrogen (TN) excretion. There were significant effects of temperature and salinity, but no significant interaction between them, on ammonia-N excretion rate (R(AN)). R(AN) increased with increasing temperature, over the interval 24-32 degrees C. R(AN) was lower at 25 ppt than at 10 and 40 ppt, at all temperatures. DON excretion rate (R(DON)) was not significantly influenced by either temperature or salinity; the overall mean R(DON) was about 5.24 µg-N g -1 h -1. However, the percentages of DON in TN (P(DON)) varied from 15.4 to 36.4% under the various temperature-salinity combinations. P(DON) at 28 and 32 degrees C was significantly lower than at 24 degrees C, and P(DON) at 10 ppt was significantly lower than at 25 and 40 ppt. Only very small amounts of nitrogen were excreted by L. vannamei as nitrite-N and nitrate-N.