Acute toxicity of nitrite on white shrimp Litopenaeus vannamei (Boone) juveniles in low‐salinity water

The nitrite toxicity was estimated in juveniles of L. vannamei. The 24, 48, 72 and 96 h LC₅₀ of nitrite‐N on juveniles were 8.1, 7.9, 6.8 and 5.7 mg L^?1 at 0.6 g L^?1; 14.4, 9.6 8.3 and 7.0 mg L^?1 at 1.0 g L^?1; 19.4, 15.4, 13.4 and 12.4 mg L^?1 at 2.0 g L^?1 of salinity respectively. The tolerance of juveniles to nitrite decreased at 96 h of exposure by 18.6% and 54.0%, when salinity declined from 1.0 to 0.6 g L^?1 and from 2.0 to 0.6 g L^?1 respectively. The safe concentrations at salinities of 0.6, 1.0 and 2.0 g L^?1 were 0.28, 0.35 and 0.62 mg L^?1 nitrite‐N respectively. The relationship between LC₅₀ (mg L^?1), salinity (S) (g L^?1) and exposure time (T) (h) was LC₅₀ = 8.4688 + 5.6764S – 0.0762T for salinities from 0.6 to 2.0 g L^?1 and for exposure times from 24 to 96 h; the relationship between survival (%) and nitrite‐N concentration (C) for salinity of 0.6–2.0 g L^?1, nitrite‐N concentrations of 0–40 mg L^?1 and exposure times from 0 to 96 h was as follows: survival (%) = 0.8442 + 0.1909S – 0.0038T – 0.0277C + 0.0008ST + 0.0001CT–0.0029SC, and the tentative equation for predicting the 96‐h LC₅₀ to salinities from 0.6 to 35 g L^?1 in L. vannamei juveniles (3.9–4.4 g) was 96‐h LC₅₀ = 0.2127 S² + 1.558S + 5.9868. For nitrite toxicity, it is shown that a small change in salinity of waters from 2.0 to 0.6 g L^?1 is more critical for L. vannamei than when wider differences in salinity occur in brackish and marine waters (15–35 g L^?1).     

Effects of salinity on osmoregulation,growth and survival in Asian swamp eel (Monopterus albus) (Zuiew 1793)

The Asian swamp eel Monopterus albus is normally considered a freshwater species, but can also occasionally be found in brackish water. It is an obligate air‐breather with highly reduced gills, making its osmoregulation physiology interesting because the gills normally represent the primary site of osmoregulation in teleosts. Being a popular fish for human consumption, the swamp eel is cultured extensively in freshwater ponds in the Mekong Delta of Vietnam. However, very little is known about its salinity tolerance, which is becoming topical due to the increasing salt‐water intrusions into tropical deltas. We therefore studied how increased salinity affects survival, growth, blood pressure, heart rate, blood osmolality and plasma ions. All eels survived prolonged exposure to 5 and 10 g L^?1, although plasma osmolality increased significantly at 10 g L^?1. Further elevation to 15 and 20 g L^?1 was associated with significantly elevated mortality, with a corresponding increase in plasma osmolality and ion con‐centrations. Our results show that swamp eels thrive in 0–10 g L^?1 with an optimum growth between 0 and 9 g L^?1, indicating that utilization of low saline brackish waters for aquaculture is possible.     

Constructed wetlands for treatment of harvest effluents from grow‐out ponds of the Amazon river prawn

Effluent discharges from aquaculture can reduce water quality in receiving water bodies and that strategies or practices to reduce this are necessary. One possibility is to reduce, or eliminate, water renewal in grow‐out ponds. In this study, we eliminated water renewal in grow‐out ponds associated with the culture of 40 individuals m^?2 of Amazon river prawn (Macrobrachium amazonicum). At the end of the culture period it was, however, necessary to drain the pond to harvest the prawns. An experiment was performed in triplicate, in which the water supply characteristics and harvest water characteristics of ponds were evaluated. To reduce these concentrations of total N and P, an aquatic macrophyte (Eichhornia crassipes, water hyacinth) treatment system (CWs) was adopted. The water characteristics in the CWs were evaluated after 1, 3, 7, 14 and 21 days. The water supply of ponds presented the average concentrations of 0.67 ± 0.32 mg L^?1 and 17.4 ± 14.7 μg L^?1 of total‐N and total‐P respectively. The harvest effluent of ponds had elevated concentrations of different forms of nitrogen (4.44 mg L^?1 of total‐N) and phosphorous (100.9 μg L^?1 of total‐P). After 1 day of the experiment we found the following reductions in key nutrients in treatment system containing E. crassipes: 90%, 78% and 45% reductions in the concentrations of particulate matter, orthophosphates and nitrates respectively. We noted that after 3 days the nitrates had been reduced by 53%. We concluded that 3 days of this treatment was sufficient for the removal of the additional nutrients that had accumulated in the Amazon river prawn ponds.     

Effects of stocking density and water conditioners on yolk‐sac larvae of two marine finfish during simulated air transport

As marine finfish aquaculture expands, there is an increasing interest in the ability to ship early life stages from breeding centres to hatcheries so that each hatchery does not have to maintain its own broodstock. Here, we conducted 24 h air‐shipping simulations with yolk‐sac larvae of California yellowtail (CYT; Seriola lalandi) and white seabass (WSB; Atractoscion nobilis) to help fill in the informational gaps for shipping marine fish larvae. We examined the effects of a pH buffer on water quality, post‐shipping larval survival and subsequent survival to first feeding at larval densities of 1000, 3000, 6000 and 9000 larvae L^?1. The pH buffer, 8.3 Trizma^®, was tested at varying concentrations of zero (NT = 0.00 g L^?1), low (LT = 0.75 g L^?1), medium (MT = 1.5 g L^?1) and high (HT = 3.0 g L^?1). Trials were conducted using replicate 2 L aquarium bags filled with 500 mL of seawater and held in a water bath at 19–20°C. Results showed an interspecific difference in survival at the highest shipping densities under these experimental conditions. Shipping densities up to 6750 CYT larvae L^?1 or 3000 WSB larvae L^?1 consistently yielded >90% survival immediately after simulated shipment and >85% survival 48 h after the simulations. Furthermore, at these densities, pH was maintained at ~8.0 when buffered at 1.5 g L^?1. The highest tested densities of 9580 CYT larvae L^?1 and 9940 WSB larvae L^?1, yielded lower survival 69–79% and 0.0–1.3% respectively after 24 h. Final pH in the high density CYT trials were unsatisfactory (below 7.0), regardless of the buffer concentration; however pH in the WSB high density trials improved with increasing buffer concentration. On the basis of the results from these air‐shipping simulations, we recommend CYT and WSB larvae be shipped in seawater with 1.5 g L^?1 Trizma^® at densities not greater than 6750 larvae L^?1 for CYT and 3000 larvae L^?1 for WSB. We believe this represents an important step in improving long distance transport protocols for these species and provides useful guidance in air transport of other economically and ecologically important marine species. Additional research is warranted to compare these simulation results with those from actual air shipments, as we did not account for factors that may vary in flight like temperature and pressure variations, and physical agitation.     

Survival and behavioural responses of cool and warm water fish sedated with AQUI‐S®20E (10% eugenol) at high loading densities

This study evaluated the effects of AQUI‐S^®20E (10% eugenol) sedation on the survival and behaviour of yellow perch Perca flavescens (Mitchill) and Nile tilapia Oreochromis niloticus L. held in high loading densities. Fish were held in 0–300 mg L^?1 AQUI‐S^®20E (0–30 mg L^?1 eugenol) for up to 10 h in static tanks. At 17°C, yellow perch held in 200 and 300 mg L^?1 AQUI‐S^®20E were lightly sedated for up to 7 h. Yellow perch at 200 and 300 mg L^?1 AQUI‐S^®20E also had >95% mean survival 7‐days post exposure using loading densities up to 360 g L^?1. Nile tilapia were only sedated for ≤3 h in concentrations up to 300 mg L^?1 at 22°C and had >90% mean survival at loading densities ≤480 g L^?1. Ammonia in tanks increased significantly as loading density increased, but treatment with AQUI–S^®20E did not reduce ammonia accumulation. Results suggest that AQUI–S^®20E was effective to sedate yellow perch and Nile tilapia at high loading densities, but sedation varied with loading density and species.     

An optimized and simplified method for analysing urea and ammonia in freshwater aquaculture systems

This study presents a simple urease method for analysis of ammonia and urea in freshwater aquaculture systems. Urea is hydrolysed into ammonia using urease followed by analysis of released ammonia using the salicylate‐hypochlorite method. The hydrolysis of urea is performed at room temperature and without addition of a buffer. A number of tests were performed on water samples obtained from a commercial rainbow trout farm to determine the optimal urease concentration and time for complete hydrolysis. One mL of water sample was spiked with 1.3 mL urea at three different concentrations: 50 μg L^?1, 100 μg L^?1 and 200 μg L^?1 urea‐N. In addition, five concentrations of urease were tested, ranging from 0.1 U mL^?1 to 4 U mL^?1. Samples were hydrolysed for various time periods ranging from 5 to 120 min. A urease concentration of 0.4 UmL^?1 and a hydrolysis period of 120 min gave the best results, with 99.6–101% recovery of urea‐N in samples spiked with 100 or 200 μg L^?1 urea‐N. The level of accurate quantification of ammonia using the method is 50 μg L^?1 NH₄⁺‐N, and the detection level is 5–10 μg L^?1 NH₄⁺‐N.     

Effects of acute change in salinity and moulting on the infection of white leg shrimp (Penaeus vannamei) with white spot syndrome virus upon immersion challenge

In the field, moulting and salinity drop in the water due to excessive rainfall have been mentioned to be risk factors for WSSV outbreaks. Therefore, in this study, the effect of an acute change in environmental salinity and shedding of the old cuticle shell on the susceptibility of Penaeus vannamei to WSSV was evaluated by immersion challenge. For testing the effect of abrupt salinity stress, early premoult shrimp that were acclimated to 35 g L^?1 were subjected to salinities of 50 g L^?1, 35 g L^?1, 20 g L^?1, 10 g L^?1 and 7 g L^?1 or 5 g L^?1 and simultaneously exposed to 10^5.5 SID₅₀ mL^?1 of WSSV for 5 h, after which the salinity was brought back to 35 g L^?1. Shrimp that were transferred from 35 g L^?1 to 50 g L^?1, 35 g L^?1 and 20 g L^?1 did not become infected with WSSV. Shrimp became infected with WSSV after an acute salinity drop from 35 g L^?1 to 10 g L^?1 and lower. The mortality in shrimp, subjected to a salinity change to 10 g L^?1, 7 g L^?1 and 5 g L^?1, was 6.7%, 46.7% and 53.3%, respectively (P < 0.05)_. For testing the effect of moulting, shrimp in early premoult, moulting and post‐moult were immersed in sea water containing 10^5.5 SID₅₀ mL^?1 of WSSV. The resulting mortality due to WSSV infection in shrimp inoculated during early premoult (0%), ecdysis (53.3%) and post‐moult (26.72%) demonstrated that a significant difference exists in susceptibility of shrimp during the short moulting process (P < 0.05). The findings of this study indicate that during a drop in environmental salinity lower than 10 g L^?1 and ecdysis, shrimp are at risk for a WSSV infection. These findings have important implications for WSSV control measures.     

Larval development and salinity tolerance of Japanese flounder (Paralichthys olivaceus) from hatching to juvenile settlement

Salinity tolerance and growth of Japanese flounder Paralichthys olivaceus at different developmental stages were evaluated, including newly hatched larvae (nhl), yolk sac larvae (ysl), oil droplet larvae (odl), post oil droplet larvae (podl), premetamorphic larvae (preml) and prometamorphic larvae (proml), at 11 salinities from 5 to 55 g L^?1 for 96 h. The ontogenesis during the early life of P. olivaceus was investigated under hatchery salinity 35 g L^?1. The results showed that suitable salinities for nhl, ysl, odl, podl, preml and proml larvae were 10 to 25 g L^?1, 10 to 30 g L^?1, 20 to 30 g L^?1, 30 g L^?1, 10 to 30 g L^?1, 15 g L^?1, respectively, demonstrating an ontogenetic variation of salinity tolerance. The salinity tolerance of nhl, ysl, preml was higher than that of odl, podl and proml. The ysl and preml larvae displayed wide salinity tolerances. The present findings demonstrate that the suitable salinity for larviculture of P. olivaceus is 20–25 g L^?1 before the depletion of oil droplet; after that, higher salinity (30 g L^?1) should be ensured for the post‐oil droplet larvae; the premetamorphic larvae can be cultured at a wide salinity range (10–30 g L^?1), and the metamorphosed larvae should be reared at salinity about 15 g L^?1.     

Effects of incubation water hardness and salinity on egg hatch and fry survival of Nile tilapia Oreochromis niloticus (Linnaeus)

This study examined the effects of water hardness and salinity on yolk sac larvae and swim‐up fry survival of Nile tilapia, Oreochromis niloticus (Chitralada strain), eggs during artificial incubation. Four experiments were conducted to evaluate the effects of hardness, salinity and the sources of saline incubation water. High water hardness treatments (500–4200 mg L^?1 as CaCO₃) resulted in higher yolk sac larvae and swim‐up fry survival than low water hardness treatments (50.0 and 132 mg L^?1 as CaCO₃); although yolk sac larvae and swim‐up fry survival did not differ among the high or low hardness treatments. Salinity of 4.0 g L^?1 using seawater, and 4.0 and 8.0 g L^?1 using unprocessed common salt resulted in the higher survival rate of yolk sac larvae and swim‐up fry than other salinity treatments. Yolk sac larvae and swim‐up fry survival was found to decrease with the increase in salinity and increase with the increase in water hardness. The present study demonstrated the positive effects of increased water hardness level (>132 mg L^?1) on yolk sac larvae and swim‐up fry survival. The study also showed that seawater salinity of 4 g L^?1 was the most appropriate salinity level for incubating Nile tilapia eggs.     

Rhodovulum sulfidophilum,a phototrophic bacterium,grown in palm oil mill effluent improves the larval survival of marble goby Oxyeleotris marmorata (Bleeker)

Survival of marble goby larvae fed either Rhodovulum sulfidophilum, a phototrophic bacterium cultured from palm oil mill effluent (pPB), or microalgae ( Nannochloropsis sp.) was evaluated at two salinities. Larvae directly fed pPB had survival of 0–29% at 5 g L^?1 salinity and 0–19% at 10 g L^?1 salinity, whereas larvae directly fed microalgae suffered complete mortality after 20 days of culture at both salinities. However, larvae indirectly fed pPB or microalgae, i.e. via rotifers (Days 1–30) and Artemia nauplii (Days 21–30) cultured solely from pPB or microalgae, showed improved survival of 35–55% or 44–49% at 5 g L^?1 salinity respectively. In all experiments, fish larvae reared at 5 g L^?1 salinity showed significantly higher (P < 0.01) mean survival than those reared at 10 g L^?1 salinity. The survival of larvae fed the bacterial‐based diet was higher compared with microalgal diet used in previous studies. The pPB had higher total polyunsaturated fatty acids and docosahexaenoic acid (DHA) than the microalgae, which had very high eicosapentaenoic acid (EPA). Larvae with very high ratios of DHA/EPA (>11) or/and ARA (arachidonic acid)/EPA (>5), attributable to their given diet, however suffered the highest mortality.     

Effects of salinity on standard metabolic rate of juvenile marbled spinefoot (Siganus rivulatus)

Marbled spinefoot, Siganus rivulatus, is a herbivorous euryhaline teleost widely distributed in the Eastern Mediterranean. It is an economically valuable species and a suitable candidate for warm water aquaculture. Accordingly, understanding the effects of environmental factors on fish metabolism is important to optimize culture conditions. Two experiments were performed to establish standard metabolic rate and study the effect of salinity on metabolism of marbled spinefoot. In the first experiment, a series of flow‐through respirometry experiments was performed at 27°C and 35 g L^?1. The standard metabolic rate of marbled spinefoot juveniles was calculated as 0.57 ± 0.02 mg O₂ g^?1 h^?1 (mean ± SE). In the second experiment, fish were maintained at salinities of 25, 30, 35 and 40 g L^?1 for 2 weeks. Flow‐through respirometry was performed to measure respiration rates at the various salinities. Respiration rates were similar among fish in salinities of 30, 35 and 40 g L^?1 but increased significantly at 25 g L^?1. Results suggest that despite the euryhalinity of marbled spinefoot, farmers should maintain salinity within the optimal range of 30–40 g L^?1 in order to improve productivity.     

Curcuma longa supplementation in the diet of Astyanax aff. bimaculatus in preparation for transport

The physiological state of fish before transportation is an important aspect to be observed when reduction in losses due to mortality is aimed. Various preparative procedures for transport are reported, but little is known about the use of additives in fish diet. In this study, we aimed to evaluate the effect of dietary turmeric (Curcuma longa) supplementation on the tolerance of juvenile Astyanax aff. bimaculatus to transportation stress. The experimental design consisted of six treatments: 0, 20, 40, 60, 80 and 100.0 g kg^?1 turmeric. Fish weighing 0.83 ± 0.04 g were distributed in 24 80‐L aquaria at a density of 0.5 fish L^?1 and were fed to satiation three times a day for 60 days. After this period, fish were transported for 24 h in plastic bags (15 fish per bag). Using a discontinuous linear response plateau (LRP) model, the lowest estimated concentration of turmeric that maximized the survival rate was 16.67 g kg^?1. Quadratic effects of turmeric on blood lactate levels were observed, and the estimated concentration of turmeric required to minimize blood lactate levels was 64.7 g kg^?1. We observed quadratic effects of turmeric on superoxide dismutase activity and the concentration of malondialdehyde in fish gills and the turmeric concentrations required to minimize the transport stress effects on these variables were 42.50 and 83.33 g kg^?1, respectively. Thus, dietary supplementation with turmeric enhanced the tolerance of juvenile A. aff. bimaculatus to transportation stress.     

Effect of different feeds on the growth,survival and reproductive performance of zebrafish,Danio rerio (Hamilton, 1822)

Present experiment was conducted to determine the effect of different feeds with varying protein levels on the growth, survival and reproductive performance of zebrafish, Danio rerio. The control diet (T1) was wild‐collected zooplankton from local fish ponds, while test diets with 350 g kg^?1 protein (T2), 400 g kg^?1 protein (T3) and 450 g kg^?1 protein (T4) were formulated and fed to fish for a period of 210 days. The significantly (P < 0.05) highest mean weight gain and specific growth rate were observed in T1, which were similar with T3 and T4. The significantly (P < 0.05) highest number of egg production per female and relative fecundity were found in T1, followed by T4 and T3 while T2 produced lowest number of eggs. No significant (P > 0.05) differences were observed in brood survival rate, fertilization and hatching rate among the dietary treatments. The highest (P < 0.05) fry survival rate was recorded in T1, followed by T3 and T4. Thus, it is suggested that control diet i.e. mixed zooplankton exhibited better growth, reproductive performance and fry survival rate. However, diet containing 400 g kg^?1 crude protein also gave comparable results in terms of growth, survival and reproductive performance of zebrafish.     

The effects of salinity on reproductive performance and plasma levels of sex steroids in Caspian kutum Rutilus frisii kutum

Sexually mature kutum, Rutilus frisii kutum, captured from its natural habits, the Caspian Sea and the Khoushkrood River, reared at 0.5 g L^?1 and 8–13 g L^?1 for approximately 1 year in experimental condition, for assessing the effect of salinity on reproduction. Plasma concentrations of sex steroid hormones (17β‐estradiol, testosterone and 17α‐hydroxyprogestrone) were measured in the three stages of gametogenesis. Female kutum held at <0.5 g L^?1 or 8–13 g L^?1 had no ovulated oocytes in their ovaries. In contrast, males held in captivity were spermiated, similar to their wild counterparts. The average sperm volume of males held at <0.5 g L^?1 (2.36 ± 0.46 mL) was lower than males held at 8–13 g L^?1 (3.65 ± 0.73 mL) at the end of the experimental period. The highest concentration of testosterone was observed in mid‐gametogenesis in wild fish that was significantly higher than the concentration seen in fish held in either <0.5 g L^?1 or 8–13 g L^?1. Female kutum showed suppressed steroid hormones in captivity, resulting in failure in the gonad development. However, male kutum adapt well to captivity and showed synchrony in steroid hormone variations with the wild fish, resulting in the testicular development. Results of this study also indicate that salinity plays a minor, but vital, role in reproduction of kutum, a factor that needs to be considered for keeping broodstock of brackish water fish species like kutum.     

Physiological responses and HSP70 mRNA expression in GIFT tilapia juveniles,Oreochromis niloticus under short‐term crowding

Physiological responses and HSP70 mRNA expression to short‐term crowding were tested in juveniles genetically improved farmed tilapia (Oreochromis niloticus) (70.43 ± 4.43 g). Fish were kept at control group (5 g L^?1) and stress groups (low density 10 g L^?1, medium density 40 g L^?1 and high density 70 and 100 g L^?1) for 48 h. Each density was tested in triplicates. The effects of a short‐term exposure on the physiological responses of fish were determined before stress (0 h) and at 6, 12, 24 or 48 h post‐crowding. There was a significant increase in serum cortisol, total protein, lysozyme and aspartate aminotransferase (AST) activities in all stressed groups at 24 h post‐crowding (P < 0.05). Serum glucose and alanine aminotransferase (ALT) of 100 g L^?1 stressed group were lower than that of the control after 48 h of crowding stress (P < 0.05). The levels of serum triglyceride and cholesterol in crowding stress with high density were significantly decreased compared with the control group at 48 h. The mRNA expression data showed that hepatic HSP70 mRNA levels were markedly elevated at all stressed groups. HSP70 mRNA levels of 70 and 100 g L^?1 stressed groups decreased at 48 h compared with the 24 h post‐crowding. The protective ability of HSP70 was limited.     

Protection of crucian carp (Carassius auratus Gibelio) against septicaemia caused by Aeromonas hydrophila using specific egg yolk immunoglobulins

Egg yolk immunoglobulins (IgY) were obtained from laying hens immunized with inactivated Aeromonas hydrophila. The purified IgY was shown to inhibit the growth of A. hydrophila in vitro and the optimum concentration for inhibition of A. hydrophila‐specific IgY was 75 mg mL^?1. In a subsequent challenge trial, 100 carp (200~250 g) were assigned to one of ten tanks with ten carp per tank. The fish in one tank were unchallenged whereas the remaining 90 fish were injected intraperitoneally with 100 μL of A. hydrophila at a concentration of 10⁸ cfu mL^?1. For the next 21 days, all fish were moved in their respective groups to a clean tank for 20 min day^?1. The fish in four tanks (one unchallenged tank and three challenged tanks) received no treatment whereas the fish in the remaining six tanks were immersed in either 0.5 g L^?1 aqueous nonspecific IgY (N = 3) or 0.5 g L^?1 aqueous specific IgY (N = 3). Haemoglobin concentrations, white and red blood cell numbers as well as the mortality of specific IgY‐treated fish were significantly different from those of the control. These results suggest that passive immunization by immersion with pathogen‐specific IgY may provide a valuable treatment for A. hydrophila infection in carp.     

Effect of choline chloride as an osmoregulator as well as its role in growth and the biochemical content of postlarval kuruma shrimp; Marsupenaeus japonicus (Bate)

A 45‐day feeding experiment was conducted to examine two levels of dietary choline chloride (CC) [0.6 and 1.2 g kg^?1 CC] against control (0.0 g kg^?1 CC) on the biological, biochemical composition and stress tolerance of postlarval (PL‐20) Marsupenaeus japonicus. The results showed improvements in some biochemical contents such as phosphatidylcholine (PC) and methionine (Met) as 0.6 and 1.2 g kg^?1 dietary CC significantly (P < 0.05) increased both PC and Met contents of shrimp carcass more than those of the control group. The results also showed that supplemental (0.6 g kg^?1) choline could improve (P < 0.05) PC/PE (phosphatidylethanolamine) ratio. Growth parameters of the shrimp group that received 0.6/1.2 g kg^?1 dietary CC showed a significant (P < 0.05) improvement. In case of osmotic stress test, 0.6 g kg^?1 supplemented CC level showed significantly (P < 0.05) longer LT‐50 (the lethal time needed to kill half of the population) than the other shrimp groups that received 0.0 and 1.2 g kg^?1 dietary CC levels. This study showed the efficacy of 0.6 g kg^?1 dietary choline to improve the osmotic tolerance of kuruma shrimp as well as growth, survival and biochemical contents of postlarval kuruma shrimp.     

Investigation of tetracycline and degradation products in Euphrates river receiving outflows of trout farms

In this study, tetracycline (TC), epitetracycline (ETC), 4‐epianhydrotetracycline (EATC) and anhydrotetracycline (ATC) concentrations were determined in the surface waters carrying outflows of trout farms. The samples were taken from downstream of Keban Dam and upstream of Karakaya Dam Lake, which are located in the Euphrates and Tigris River Basin. The occurrence of TC and degradation products (DPs) was proved in the sampling points which take the outflows of the trout farms. Tetracycline and DPs were under the detection limits in sampling points where the trout farms do not exist. The highest TC concentration was detected as 50.0 ± 2.5 μg L^?1 (1st week), whereas the lowest TC concentration was 8.2 ± 0.41 μg L^?1 (7th week). The highest ETC concentration was 88.1 ± 4.4 μg L^?1 (3rd week)and the lowest ETC concentration was 9.4 ± 0.4 μg L^?1 (3rd week). The highest and lowest EATC concentrations were detected as 35.8 ± 1.8 μg L^?1 (2nd week) and 8.2 ± 0.4 μg L^?1 (2nd week) respectively. The highest ATC concentration was 28.3 ± 1.4 μg L^?1 (3rd week), whereas the lowest was 6.54 ± 0.34 μg L^?1 (7th week). Tetracycline and DP concentrations detected in surface waters followed the following order: ETC>TC>EATC>ATC.     

Dietary leucine requirement of Juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to evaluate the effects of dietary leucine on growth performance, feed utilization, body composition and non‐specific immune responses of juvenile Nile tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐leucine (5.3, 8.1, 10.9, 13.2, 15.6 and 18.1 g kg^?1 diet, respectively) from dietary ingredients and crystalline L‐leucine. Each diet was randomly assigned to triplicate groups of 20 juvenile fish (1.94 ± 0.01 g) three times daily to apparent satiation. Results showed that the weight gain (WG) and specific growth rate (SGR) increased as dietary leucine concentrations increased from 5.3 to 13.2 g kg^?1 and then decreased slightly with further increase in dietary leucine concentrations. Quadratic regression analysis (y = ?522.6x² + 1304.x + 132.6, R² = 0.684) on weight gain against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 12.5 g kg^?1 diet (corresponding to 43.1 g kg^?1 of dietary protein). Leucine supplementation had no impact on the survival and body composition of tilapia. Serum lysozyme activity of fish fed diet containing 13.2 g kg^?1 leucine significantly increased compared to fish fed diet containing 5.3 g kg^?1. Serum superoxide dismutase activity and immunoglobulin M (IgM) concentration were not significantly affected by dietary leucine supplementation.     

Effects of replacing fish oil with stearine as main lipid source in diet on growth and survival of Pacific White Shrimp,Litopenaeus vannamei (Boone, 1931)

The stearine fraction from raw fish oil refinement has been treated as a waste material. This study was conducted to evaluate effects of replacing prime refined fish oil with stearine as the main lipid source to a control diet on shrimp growth and survival as well as on pellet water stability of diets. Test diets were processed containing three levels (0.7%, 1.3% and 2.7%) of either stearine or refined fish oil in a semi‐purified control diet. These diets were each assigned to five or six replicated tanks and each tank was stocked with seventeen juvenile shrimp (ca. 0.50 g) in an indoor seawater recirculating system. At the end of 6 weeks, the survival of shrimp was 89.4–95.3% with no significant difference (P > 0.05) among dietary treatments. The six test diets obtained significantly higher (P < 0.05) shrimp growth rates (1.46–1.83 g week^?1) than the control diet (1.38 g week^?1). The shrimp that were fed the three stearine‐added diets exhibited high growth rates (1.75–1.83 g week^?1). Increasing the inclusion level of the stearine improved pellet water stability (91.7–93.9%; P < 0.05). These results suggest that stearine can replace fish oil in shrimp feed based on the growth performance.