Effect of different diets on growth and digestive enzyme activity in Litopenaeus vannamei (Boone, 1931) early post-larvae

Growth rate, soluble-protein content and digestive-enzyme activities were studied in Litopenaeus vannamei (Boone, 1931) early post-larvae under six feeding regimens, which included combinations of freshly hatched Artemia nauplii, an artificial diet and algae. Growth (0.11 mg DW day⁻¹) and soluble-protein content (61.8 μg protein larvae⁻¹ at PL₁₀) of post-larvae fed mixed diets were significantly higher (P < 0.05). An artificial diet used alone or co-fed with algae caused the lowest growth (0.03–0.05 mg DW day⁻¹) and soluble-protein content (13.7–15.5 μg protein larvae⁻¹ at PL₁₀). Trypsin-like activity was higher (up to 10 times) in post-larvae fed Artemia nauplii and an artificial diet alone or plus algae. The artificial diet stimulated chymotrypsin activity, apparently in response to squid meal present in this diet. Amylase activity increased when post-larvae were fed the artificial diet. This was apparently related more to the origin of the starch than to the total carbohydrate level of the diet. No obvious relationship was found between enzyme activity and growth in any feed combination. Based on growth and soluble-protein content, we determined that partial substitution (50%) of Artemia nauplii by artificial diet and the use of algae co-fed beyond the first post-larval stage benefits growth and the nutritional state of L. vannamei post-larvae.     

Experimental white spot syndrome virus challenge of juvenile Litopenaeus vannamei (Boone) at different salinities

In recent years, the shrimp industry has turned to inland freshwater culture as one method to avoid problems such as the introduction of possible vectors of viral pathogens into seawater ponds. Our experiments evaluated susceptibility to white spot syndrome virus (WSSV) in Litopenaeus vannamei held under different salinity regimens. Juvenile L. vannamei that were conditioned at salinities of 35, 25, 15, 5 and 2 g L⁻¹ were challenged with WSSV. In order to assess the severity of white spot disease, histological analysis and nested polymerase chain reaction (PCR) tests were carried out on the challenged shrimp every 4 h after 48 h post challenge. The results indicated that significantly more severe infections resulted at 15‰ than at other salinities. Mortality could not be compared due to the sampling design and because severe WSSV infections occurred in all test groups such that few shrimp remained alive in each challenged group at the end of the test. Despite this, the results suggest that salinity may affect the course and outcome of WSSV infections.     

Effect of culture system on the nutrition and growth performance of Pacific white shrimp Litopenaeus vannamei (Boone) fed different diets

Two 8-week feeding trials were conducted with juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) to compare the growth and performance of animals fed a series of experimental and commercial pelleted shrimp and fish feeds and dietary feeding regimes within an indoor running-water culture system and an outdoor zero-water-exchange culture system. The best overall shrimp growth performance was observed for animals fed the experimental shrimp diet and all-day feeding regime under outdoor zero-water-exchange culture conditions. Final body weight and average weekly growth rate under these conditions were 2.8 and 3.4 times greater, respectively, than animals of similar size fed with the same diet under indoor running-water culture conditions. Although direct comparison between indoor and outdoor culture systems is difficult because of the lower indoor water temperatures, and consequently lower mean daily feed intake of animals, it is believed that the higher growth and feed performance of animals reared under outdoor `green-water' culture conditions was primarily due to their ability to obtain additional nutrients from food organisms endogenously produced within the zero-water-exchange culture system. The most promising features of zero-water-exchange culture systems are that they offer increased biosecurity, reduced feed costs and water use for the farmer, and by doing so provide a potential avenue of moving the shrimp culture industry along a path of greater sustainability and environmental compatibility.     

Biotic communities and feeding habits of Litopenaeus vannamei (Boone 1931) and Litopenaeus stylirostris (Stimpson 1974) in monoculture and polyculture semi-intensive ponds

Zooplankton, macrozoobenthos and feeding habits of Litopenaeus stylirostris and L. vannamei in monoculture and polyculture semi‐intensive experimental ponds were evaluated. Zooplankton was more abundant in monoculture of L. stylirostris (1002±670 organisms (org.) L^?1) than in monoculture of L. vannamei (470±37 org. L^?1), and polyculture (321±188 org. L^?1). The main zooplanktonic groups were polychaeta larvae, nauplii, copepods and polychaeta. Macrozoobenthos was more abundant in polyculture (6898±11 137 org. m^?2) compared with monoculture of L. stylirostris (3201±350 org. m^?2) and L. vannamei (2384±3752 org. m^?2). The main benthic groups were copepods, polychaeta, ostracods, nematodes and insects. Differences in feeding habits were found between species and regimes. Litopenaeus vannamei showed to be a more voracious species and fed mostly on organic detritus and benthos in both culture regimes. Litopenaeus stylirostris had a more restricted sources of feed in the ponds. The major component in the stomach content of both species was detritus. Macroalgae, sand, exuvia, formulated feed, prey and microalgae were minor components for both species (<7%). Ingestion of formulated feed was <4% for L. stylirostris and was not detected for L. vannamei. The stomach repletion rates were larger for L. vannamei (55.6% and 48.8%) than for L. stylirostris (43.75% and 44.89%). Litopenaeus stylirostris grew better in polyculture (10.3±3.4 g) that in monoculture (9.0±3.8 g). Litopenaeus vannamei grew better in monoculture (16.1±4.8 g) than in polyculture (13.4±4.5 g). For both species, feed conversion ratio was lower in polyculture.     

Effect of Diet Size on Feeding Behavior and Growth of Pacific White Shrimp,Litopenaeus vannamei

Abstract

Six diet sizes, manufactured from crumbling large pellets, were investigated for their effect on the feeding behavior and growth of Pacific white shrimp, Litopenaeus vannamei. These diets containing 44.7% protein and 8.2% lipid were fed to 0.9 g shrimp for a period of eight weeks under indoor controlled laboratory conditions. Shrimp were stocked at a density of 12 animals per 52 L aquarium (50/m²) and were evaluated for feeding behavior, final weight, growth rate, feed conversion ratio (FCR), and survival. Feeding behavior was observed weekly starting at the beginning of the 4th week until the end of the trial. Results indicated that the variation in diet sizes did not produce significant differences in shrimp growth, FCR or survival. However, shrimp feeding behavior (in terms of total attacking incidents during feeding) was significantly different among diet sizes. This shrimp behavior was observed more frequently in aquaria fed larger diet size (3.0 mm pellet) as compared with those fed smaller diet sizes (0.7 mm and 1.2 mm crumbles). When shrimp were fed larger pellets, some of the individuals obstruct other individuals and monopolize the diet. Such “selfish” behavior of shrimp could result in considerable size variation and severe mortality of smaller individuals, which could be the case when shrimp are reared to market size. The effect of diet size on shrimp feeding behavior deserves further investigation and the use of a continuous monitoring device such as a video camera is strongly recommended. Future study should also consider various shrimp and pellet sizes more meaningful to aquaculture producers.     

Activity pattern of the marine shrimp Litopenaeus vannamei (Boone 1931) in laboratory as a function of different feeding frequencies

Management practices on most Brazilian shrimp farms have resulted in high expenses for producers and damage to the environment. Applied ethology could provide information on the pattern of shrimp activity, enabling more efficient feeding frequencies. Behavioural activities of the shrimp Litopenaeus vannamei were recorded during different feeding frequencies. The shrimp were kept in aquariums on a 12:12 h light/dark cycle. They were fed commercial ration three (at 6:00, 12:00 and 18:00 hours), four (at 6:00, 10:00, 14:00 and 18:00 hours) or seven times per day (at 6:00. 8:00, 10:00, 12:00, 14:00, 16:00 and 18:00 hours). We observed animals at 15 min^?1 aquarium^?1 time periods, recording feeding, substrate exploration, swimming and inactivity. Feeding and exploration were the highest for shrimp fed three times per day, swimming was greatest when animals received four feedings, whereas inactivity was higher for shrimp fed seven times per day. There was greater food ingestion between 12:00 and 14:00 hours for animals fed three and four times per day, whereas swimming was high mainly at 18:00 hours for shrimp fed three and seven times per day. The results indicate higher forage‐related activities (exploration/ingestion) when feed was offered three or four times, suggesting optimization in the pattern of shrimp activities based on these feeding frequencies.     

Digestive enzyme activity and food ingesta in juvenile shrimp Litopenaeus vannamei (Boone, 1931) as a function of body weight

A study was conducted to evaluate variations of digestive enzyme activities in Litopenaeus vannamei (Boone) reared in commercial ponds under semi‐intensive conditions. Shrimp were collected at each body weight increase of 2 g. As the shrimp grew (2–12 g), significant increases in the activities of lipase and chymotrypsin were observed. The total protease activity decreased from 6 g onwards. Trypsin activity showed a peak at 6 g and amylase activity increased two‐fold after 2 g. Additionally, the stomach contents were analysed microscopically for shrimp between 2 and 10 g. Plant matter contributed above 30% of the total stomach content in 6‐, 8‐ and 10‐g shrimp. Detritus represented 58% and 62% of the total stomach content in 2‐ and 4‐g shrimp, respectively, decreasing to 33–43% at greater shrimp weights. Artificial feed showed a maximum contribution of 20% in 6‐g shrimp. The present results show changes in the enzyme activity after the shrimp reach 6 g in body weight, evidenced by a decrease in total protease and an increase in lipase and amylase activities. The amylase/protease ratio was 2.6 in 2‐g shrimp and increased steadily to 9.6 in 12‐g shrimp. These findings suggest an adaptation of the enzymatic activity to diets with lower protein content as body weight increases, and may be related to the variation of the different items found in the stomach.     

低盐度条件下的凡纳滨对虾幼虾亮氨酸营养需求

为了探讨低盐度(0.6～0.8 g/L)条件下初始体质量为(0.38±0.004)g的凡纳滨对虾(Litopenaeus vannamei)幼虾的亮氨酸需求量,以鱼粉、花生麸和L-晶体氨基酸为蛋白源配制含粗蛋白400 g/kg的6种等氮饲料,标记为L7～L12组,各组亮氨酸水平分别为15.95、17.95、19.95、21.95、23.95和25.95 g/kg(饲料干物质).每组3个重复,每个重复30尾虾,进行56 d生长实验.结果表明,凡纳滨对虾幼虾的增重率随饲料亮氨酸水平的升高而升高,当亮氨酸水平达到23.95 g/kg(L11组)时,增重率达到最高值(1143.11±36.40)％,显著高于L7组(P＜0.05);亮氨酸水平继续提高,增重率变化不显著(P＞0.05).幼虾的蛋白质效率、全虾体蛋白沉积率和血淋巴总蛋白随着饲料亮氨酸水平的升高呈现升高趋势,最高值出现在L11组,并显著高于L7组(P＜0.05).各实验组饵料系数、血淋巴谷丙转氨酶、谷草转氨酶活性和尿素氮含量则呈现降低的趋势,最低值出现在L11组,且显著低于L7组(P＜0.05).以增重率为指标,根据折线模型可知,低盐度条件下凡纳滨对虾幼虾的亮氨酸最适需要量为24.80 g/kg饲料,即61.99 g/kg饲料蛋白.     

Feeding responses of juvenile shrimp Litopenaeus vannamei (Boone) fed at different frequencies under laboratory conditions

In shrimp farms, food partitioning during the course of the day is contradictory, ethology studies may help in determining the proper frequency. Litopenaeus vannamei juveniles were placed in 30 L aquariums (41 m⁻²), exposed to a 12:12 h light–dark cycle. Feeding was provided at 10% of biomass three, four and seven times per day, with observations made in 15 min h⁻¹ windows, initiated after the ration was offered. Latency to access the feeding tray and to start eating was recorded using instantaneous focal sampling and digestive tract filling (DTF) by the continuous focal method. Weight gain was recorded at the end of the experiment. We performed seven repetitions, with 28 individuals observed for 33 days for each treatment (490 h of observation). The three-times offering induced less latency for accessing the tray and for ingesting the feed as well as a higher DTF when compared with the other frequencies. Animals fed three and four times had similar weight gains, and were greater than those fed seven times. Our results indicate that a more spaced food offering stimulates the search for and ingestion of feed. As compared with other frequencies, the three-times-per-day option assumes lower labour costs and a more efficient use of the feed.     

Physiological, metabolic and haematological responses in white shrimp Litopenaeus vannamei (Boone) juveniles fed diets supplemented with astaxanthin acclimated to low-salinity water

The effects of dietary astaxanthin supplemented at 0, 40, 80 or 150 mg astaxanthin kg⁻¹ on growth, survival, moult frequency, osmoregulatory capacity (OC) and selected metabolic and haematological variables in Litopenaeus vannamei acclimated to low‐salinity water (3 g L⁻¹) were evaluated. Supplemented astaxanthin at 80 mg kg⁻¹ improved growth, survival and moult frequency in shrimp. The lowest OC was also exhibited in shrimp fed with dietary astaxanthin at 80 mg kg⁻¹. Shrimp haemolymph concentrations of glucose, lactate, haemocyanin and total haemocyte count were all significantly enhanced by feeding the diet supplemented with 80 mg astaxanthin kg⁻¹ compared with shrimp fed with the other diets. On the basis of these results, dietary astaxanthin supplementation of 80 mg kg⁻¹ is recommended for juvenile L. vannamei cultured in low‐salinity water.     

Use of commercial fermentation products as a highly unsaturated fatty acid source in practical diets for the Pacific white shrimp Litopenaeus vannamei

Removal or reduction of marine ingredients (MI) from feed formulations is critical to the sustainability of the aquaculture industry. By removing MI, diets may become limiting in several nutrients including highly unsaturated fatty acids (HUFA) such as docosahexaenoic acid (DHA) and arachidonic acid (ArA). To reduce reliance on MI in shrimp diets, two trials were conducted with Litopenaeus vannamei juveniles to determine the feasibility of using fermentation meals rich in DHA and ArA as the primary source for HUFA. A practical diet with no MI was formulated with/without DHA and ArA supplements and fed in the first trial. A diet with menhaden fish oil or a combination of plant oil with/without DHA and ArA supplements was used in the second trial. To determine whether HUFA is only needed in the early growth stages, we also fed one group a HUFA‐supplemented diet to 5 g and then switched them to a HUFA‐supplement‐free diet. In both trials, the weights were reduced when HUFA supplements were not provided either throughout the trial or from 5 g to harvest (<16 g). These results suggest that supplementation of plant oils with DHA‐ and ArA‐rich oils from fermented products is a viable option to replace marine fish oil for L. vannamei.     

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50–1.50 g L⁻¹). Diets 1–6 were formulated to contain 360 g kg⁻¹ crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9–19.0 g kg⁻¹ dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.48±0.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg⁻¹ or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg⁻¹ dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg⁻¹ dry diet (37.8 g kg⁻¹ dietary protein).     

Apparent digestibility of selected feed ingredients for white shrimp Litopenaeus vannamei,Boone

Apparent digestibility coefficients of dry matter (DM), crude protein, crude lipid, gross energy, phosphorus and amino acids in Peruvian fish meal (FM), fermented soybean meal, extruded soybean meal, soybean meal, peanut meal, wheat gluten meal, corn gluten meal, shrimp byproduct meal, meat and bone meal (MBM), poultry meat meal and plasma protein meal (PPM) were determined for white shrimp (Litopenaeus vannamei). A reference diet (RF) and test diets (consisting of 70% RF diet and 30% of the feedstuff) were used with 0.5% chromic oxide as an external indicator. A total of 1440 shrimp (initial mean body weight 1.05 ± 0.01 g) were randomly stocked into thirty‐six 500‐L fibreglass tanks with 40 shrimp per tank and three tanks per diet. Faeces were collected from triplicate groups of shrimp by a faecal collection vessel attached to the shrimp‐rearing tank. The shrimp were fed to apparent satiation four times a day and the feeding experiment lasted for 6 weeks. Statistics indicate that apparent DM digestibilities for white shrimp (L. vannamei) were the highest for FM, ranged 52.83–71.23% for other animal products and 69.98–77.10% for plant products. The protein and lipid from plant and animal sources were well digested by white shrimp. Apparent protein and lipid digestibility were in the range 87.89–93.18% and 91.57–95.28%, respectively, in plant products, and 75.00–92.34% and 83.72–92.79%, respectively, for animal products. The white shrimp demonstrated a high capacity to utilize phosphorus in the ingredients. The apparent phosphorus digestibility ranges of animal feedstuffs and plant feedstuffs were 58.90–71.61% and 75.77–82.30% respectively. Amino acid availability reflected protein digestibility, except that in MBM, for which the availability of some amino acid was lower, possibly due to protein damage during processing. Digestibility information could promote the use of ingredient substitution in least‐cost formulated diets for white shrimp.     

Trypsin enzyme activity during larval development of Litopenaeus vannamei (Boone) fed on live feeds

Larval stages of the Pacific white shrimp, Litopenaeus vannamei (Boone) were fed standard live diets of mixed microalgae from the first to the third protozoea (PZ1 to PZ3), followed by Artemia nauplii until post‐larvae 1 (PL1). Trypsin enzyme activity for each larval stage was determined using N‐α‐p‐toluenesulphonyl‐l ‐arginine methyl ester (TAME) as a substrate. Results were expressed as enzyme content to assess ontogenetic changes during larval development. Tissue trypsin content (IU µg^?1 DW for each larval stage) was significantly highest at the PZ1 stage and declined through subsequent stages to PL1. This contrasts with previously observed patterns of trypsin development in Litopenaeus setiferus (Linnaeus) and other penaeid genera, which exhibit a peak in trypsin activity at the third protozoea/first mysis (PZ3/M1) larval stage. Litopenaeus vannamei larvae transferred to a diet of Artemia at the beginning of the second protozoea (PZ2) stage were significantly heavier on reaching the first mysis stage (M1) than those fed algae, while survival was not significantly different between treatments. At both PZ2 and PZ3 stages, trypsin content in larvae feeding on Artemia was significantly lower than in those feeding on algae. The rapid decline in trypsin content from PZ1 and the flexible enzyme response from PZ2 suggest that L. vannamei is physiologically adapted to transfer to a more carnivorous diet during the mid‐protozoeal stages.     

Effects of dietary lipid sources on growth and fatty acid composition of juvenile shrimp, Litopenaeus vannamei

This experiment was conducted to evaluate the effects of dietary lipid sources on the growth performance and fatty acid (FA) composition of juvenile shrimp, Litopenaeus vannamei. Six isoenergetic and isonitrogenous semi‐purified diets containing casein, solvent‐extracted soybean meal and gelatin as protein sources, were supplemented with 60 g kg⁻¹ of lipid sources. The lipid sources included: pollack fish oil (PO), pork lard (PL), soy oil (SO), peanut oil (PN), rapeseed oil (RO) and a mixture of pollack fish oil and soy oil (POSO 1 : 1 w/w). Each diet was fed to juvenile shrimp (0.10 g average weight) four times daily in triplicate tanks to apparent satiation (feeding ratio was about 8%) for 8 weeks. At the end of the experiment, weight gain, specific growth rate and protein efficiency ratio were significantly higher for shrimp fed the diet containing PO and the POSO mixture oil than the other lipid sources. The nutritional values of SO, RO, PN and PL were similar. Shrimp fed on PO, mixture oil of POSO and SO had better survival rates than the other lipid sources, and shrimp fed the PL had the lowest survival rate. There were significant differences in lipid contents of whole body and hepatopancreas amongst the dietary treatments; however, lipid contents of tail muscle were not significantly affected by the dietary lipid sources. Shrimps fed POSO diet had higher protein content in whole body than those fed the other lipid sources, and shrimp fed PO diet had highest crude protein content of the tail muscle. A high correlation was found between dietary FA composition and FA composition of whole shrimp. FA composition of the whole body was generally affected by dietary lipid sources, especially dietary unsaturated FA.     

Replacement of fish meal by meat and bone meal in practical diets for the white shrimp Litopenaeus vannamai (Boone)

The use of meat and bone meal (MBM) was evaluated as a replacement for fish meal in a practical diet formulated to contain 41% protein and 8% lipid. Anchovy meal was replaced by 0%, 20%, 30%, 40%, 50%, 60% and 80% of MBM (diets 1–7) respectively. Healthy post larvae of Litopenaeus vannamei were reared in an indoor, semi‐closed recirculating system. Each dietary treatment was fed to triplicate groups of 40 shrimp per tank (260 L) arranged in a completely randomized design. The shrimp were hand‐fed to near‐satiation three times daily between 07:00 and 18:00 hours for 56 days. There were no significant differences (P>0.05) in growth performance among shrimp fed diets 1–6. However, shrimp fed diet 7 had significantly lower (P<0.05) growth than those fed diet 2 or diet 4. Survival ranged from 95% to 100% and did not significantly (P>0.05) differ. Feed conversion ratio (FCR) and carcass composition of the shrimp were not significantly (P>0.05) affected by dietary treatments. No significant differences (P>0.05) in protein efficiency ratio (PER) were found among shrimp fed diets 1‐6. However, shrimp fed diet 7 had significantly lower (P<0.05) PER than those fed diet 1 or diet 4. Results showed that up to 60% of fish meal protein can be replaced by MBM with no adverse effects on growth, survival, FCR, PER and body composition of L. vannamei.     

Ammonia tolerance of Litopenaeus vannamei (Boone) larvae

The tolerance of Litopenaeus vannamei larvae to increasing concentrations of total ammonia nitrogen (TAN) using a short‐term static renewal method at 26°C, 34 g L^?1 salinity and pH 8.5 was assessed. The median lethal concentration (24 h LC₅₀) for TAN in zoea (1‐2‐3), mysis (1‐2‐3) and postlarvae 1 were, respectively, 4.2‐9.9‐16.0; 19.0‐17.3‐17.5 and 13.2 mg L^?1TAN (0.6‐1.5‐2.4; 2.8‐2.5‐2.6 and 1.9 mg L^?1 NH₃‐N). The LC₅₀ values obtained in this study suggest that zoeal and post‐larval stages are more sensitive to 24 h ammonia exposure than the mysis stage of L. vannamei larvae. On the basis of the ammonia toxicity level (24 h LC₅₀) at zoea 1, we recommend that this level does not exceed 0.42 mg L^?1 TAN – equivalent to 0.06 mg L^?1 NH₃‐N – to reduce ammonia toxicity during the rearing of L. vannamei larvae.     

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.