Effect of recovery salinity on survival of acutely stressed halibut (Hippoglossus hippoglossus L) larvae

First‐feeding halibut larvae (245‐day degrees; 40 days post hatch), reared at 34 g L^?1 salinity and 7°C, were subjected to handling and allowed to recover in a range of salinities (0–34 g L^?1) and at 10°C. Survival of the unfed larvae was determined daily for 18 days. Mortality rates approached 0 after 4 days in all treatments and presumed starvation‐induced mortality started at about 11 days post handling. By 20 days post treatments, all larvae had died. Salinities in the range of 10–20 g L^?1 produced significantly (anova , P<0.01) higher initial survival (71–95%) than salinities above 20 g L^?1 (24–48%) or below 10 g L^?1 (0–19%) and this survival pattern changed little in unfed larvae for the first 10 days following the stressor. For example, 24 hour post handling, survival of halibut was improved from 28.7±16.5% (mean±standard error, n=3) at 34.0 g L^?1 to 95.2±4.8% at 13 g L^?1. A second‐order polynomial regression of 4‐day post‐handling survival data (y=?0.002x ²+0.0603x+0.0699, r²=0.3936) predicted a maximum survival at 15.1 g L^?1 salinity. These results have important implications for halibut aquaculture and research when handling of larvae is unavoidable. For practical applications, we recommend reducing salinity of receiving waters to 15–20 g L^?1 with a slow (3–4 days) reacclimation to ambient conditions.     

Growth performance and color enhancement of goldfish,Carassius auratus,fed diets containing natural dyes extracted from annatto (Bixa orellana) seeds

ABSTRACT

The present study was conducted to evaluate growth performance and color enhancement of goldfish, Carassius auratus, fed diets containing 0, 50, 100, 200, and 250 mg kg^?1 diet of annatto dye (AD) for 60 days. The survival rate was significantly higher in fish fed 100, 200, and 250 mg AD kg^?1 diet over than these fed control and 50 mg AD kg^?1 diet (p < 0.05). AD significantly (p <0 .05) increased the pigmentation in the skin and caudal fin of goldfish in a concentration dependent manner (R² = 0.995, 0.997). The highest amount of total carotenoid deposition in fish skin and fins were given by diets containing 200–250 mg AD kg^?1 diet. The highest redness (a*) of 43.21 and yellowness (b*) of 12.53 were obtained by 250 and 50 mg AD kg^?1, respectively. The present results show that AD can be successfully used as an alternative natural carotenoid source in goldfish diets at levels of 200–250 mg AD kg^?1 diet.     

Effects of formalin on water quality and parasitic monogeneans on silver perch (Bidyanus bidyanus Mitchell) in earthen ponds

Infestations of parasitic monogenean trematodes (Lepidotrema bidyana and Gyrodactylus sp.) on freshwater silver perch (Bidyanus bidyanus Mitchell) in earthen ponds were treated with formalin (37% formaldehyde). Concentrations of 30 and 40 mg L^?1 formalin were effective, but fish in ponds treated with 20 or 25 mg L^?1 remained infested. At temperatures of 24.1–26.9°C, concentrations of 30 or 40 mg L^?1 formalin caused dissolved oxygen (DO) to decline from 10.1–11.9 to 3.0–3.3 and 1.2–1.7 mg L^?1, respectively, within 36–42 h of treatment. In addition, pH declined from 7.2–8.4 to 6.3–6.7, within 36 h and turbidity decreased over 48 h. In the ponds where DO was 1.2–1.7 mg L^?1, silver perch showed signs of severe stress, but continuous aeration (10 hp ha^?1) for 3 days and inflow of well‐oxygenated water for 6–8 h prevented mortalities. At temperatures of 13.2–15.7°C, concentrations of 30 or 40 mg L^?1 formalin caused DO to decline from 9.0–10.0 to 6.0–8.1 mg L^?1 and pH from 7.0–7.3 to 5.9–6.6 within 72 h. Total ammonia‐nitrogen increased over 72 h in ponds treated with 30 or 40 mg L^?1 formalin. Fish became re‐infested with L. bidyana in all ponds within 30 days of treatment. A concentration of 30 mg L^?1 formalin is recommended as a treatment for monogeneans on silver perch in ponds, but aeration is necessary to maintain adequate water quality at higher temperatures.     

Effects of frequency and amplitude of salinity fluctuation on the growth and energy budget of juvenile Litopenaeus vannamei (Boone)

The effects of salinity fluctuation on the growth, intermoult period and energy budget of juvenile Litopenaeus vannamei were investigated. Salinity fluctuation regimes were set in different frequencies of 2, 4 and 8 days and different amplitudes of ±2, ±5 and ±10 g L^?1 from a control salinity of 20 g L^?1. After a 48‐day feeding trial, the intermoult period of shrimp became shorter with increasing amplitude and frequency of salinity fluctuation (P<0.05). Both the frequency and the amplitude of salinity fluctuation had a significant effect on the growth rate of L. vannamei juveniles (P<0.05). At the frequency of 4 days, the highest growth rates occurred at amplitudes of 5–10 g L^?1, whereas the growth rate was the lowest at 10 g L^?1 when the frequency was reduced to 2 days. Feed intake (FI) and assimilation efficiency (AE) of shrimp were also significantly affected by the salinity fluctuation (P<0.05) and matched the growth rate response. The energy expenditures for growth (G), respiration (R), excretion (U) and exuviae (E) to the energy consumed as food (C) were not affected by salinity fluctuation. However, salinity fluctuation significantly affected the percentage of C as faeces (F), with the lowest value occurring at salinity amplitudes of 5–10 g L^?1 and frequencies of 4–8 days. Therefore, salinity fluctuations (every 4 days by ±5–10 g L^?1) result in higher growth rates than constant salinity conditions (20 g L^?1) through greater FI, enhanced feed assimilation and reduced faecal energy loss.     

草鱼养殖水体中参与氮转化途径的异养菌分析

为分析草鱼池塘中参与氮代谢的异养细菌比例及其代谢途径,从杭州郊区取得4个草鱼池塘的水样,每个水样通过涂布随即挑选100株菌株进行定性显色试验,并据此选取11株异养菌进行16S rRNA序列分析。结果表明,4个草鱼养殖池塘中NH4+-N和NO2--N的平均水平分别为5.597 mg/L和0.135 mg/L。池塘中可培养的异养菌平均为3.26×105cfu/mL,其中的89.75%参与了氮的不同代谢途径,其中31.25%的氨化菌和33.50%NO3--N(NO2--N)还原菌参与了NH4+-N的生成,32.45%的氨氧化菌参与了NH4+-N的降低;NO2--N生成途径主要包括蛋白质直接转化(11.26%)、氨氧化(4.25%)和硝酸盐氮还原(10.75%),而NO2--N降低主要通过15.50%的亚硝酸氧化菌、8.75%的NO2--N还原菌和10.75%的反硝化菌实现。结果提示,草鱼养殖水体中存在大量的异养硝化菌参与不同的氮代谢途径,且产生氨氮的异养菌比例远高于去除氨氮的菌,这是草鱼养殖水体中氨氮含量易偏高的原因。同时,11株不同功能的异养菌16SrRNA鉴定结果为寡养食单胞菌(Stenotrophomonas)6株、假单胞菌(Pseudomonas)3株、克雷伯氏菌(Klebsiella)和肠杆菌(Enterobacter)各1株,而且细菌对氮源的利用具有菌株特异性。     

Chemical surface disinfection of eggs of Baltic cod,Gadus morhua L.

The effect of two disinfectants on eggs and larvae of Baltic cod, Gadus morhua, was investigated. The eggs were disinfected for 10 min using various concentrations of either glutaraldehyde (100, 200, 400, 600 and 800 mg L^?1) or iodophor (10, 50, 100 and 150 mg L^?1), 1–4‐days post‐fertilization. Bactericidal effect of disinfection, survival to hatching, hatching success and larval abnormalities were assessed. Larval survival was recorded at 5‐, 10‐ and 15‐days post‐hatch (dph). Although Baltic cod eggs have an unusually thin chorion, they could tolerate surface disinfection. A reduction in bacterial growth was observed with increased concentrations of disinfectant (3.0 × 10⁷–1.6 × 10¹ CFU mL^?1). Abnormalities in newly hatched larvae were not related to disinfection. Survival of the yolk sac larvae was significantly better for eggs treated with 400 mg L^?1 glutaraldehyde for 10 min at 10 and 15 dph. Effective disinfection was also recorded using 100 mg L^?1 Actomar K30. Egg batch effect rather than initial bacterial concentration, disinfectant type or incubation method determined the survival of the eggs to hatching and survival of larvae. Because of the carcinogenic effect of glutaraldehyde, iodophor is recommended for routine disinfection of cod eggs.     

Isolation and culture of the marine rotifer, Colurella dicentra (Gosse, 1887), from a Mississippi Gulf Coast estuary

Few marine rotifer species (e.g. Encentrum linheii and Synchaeta cecilia) have been cultured successfully besides Brachionus plicatilis and B. rotundiformis, commonly used to rear larvae of many marine fish species. The development of culture techniques for marine rotifers smaller in size than the Brachionus species may be useful for rearing fish species for which the currently used prey are too large. We evaluated the possibility of culturing Colurella dicentra isolated from a Mississippi Gulf Coast estuary. An experiment was conducted to determine the effects of salinity (10–35 g L^?1) on its population growth rate. Rotifers were fed Nannochloropsis oculata at a density of 100 000 cells mL^?1 for 15 days. Colurella dicentra survived in water with a salinity of 10–47 g L^?1. Densities of up to 300 rotifers mL^?1 were sometimes attained in cultures. Salinity influenced C. dicentra production (P<0.001). The mean rotifer numbers at 10 g L^?1 (22 840±2604 SD), 15 g L^?1 (25 980±7071 SD) and 20 g L^?1 (19 780±1029 SD) at the end of the experiment were similar (P>0.05), but were higher (P=0.05) than numbers at 25 g L^?1 (4240±1783), 30 g L^?1 (1300±264 SD) and 35 g L^?1 (100±101 SD). The population growth rate (r) of the rotifers was the highest at 15 g L^?1 (0.37–0.42 day^?1), and the lowest at 35 g L^?1 (?0.33–0.06 day^?1). This is the first report of C. dicentra in the estuarine waters of the Gulf of Mexico, and also the first time it has been cultured successfully.     

Nitrogenous and phosphorus excretions in juvenile silver catfish (Rhamdia quelen) exposed to different water hardness, humic acid, and pH levels

This study examined ammonia, urea, creatinine, protein, nitrite, nitrate, and phosphorus (P) excretion at different water hardness, humic acid, or pH levels in silver catfish (Rhamdia quelen) juveniles. The fish were exposed to different levels of water hardness (4, 24, 50, or 100 mg L^?1 CaCO₃), humic acid (0, 2.5, or 5.0 mg L^?1), or pH (5.0, 6.0, 7.0, 8.0, or 9.0) for 10 days. The overall measured nitrogen excretions were 88.1 % (244–423 μmol kg^?1 h^?1) for ammonia, 10.9 % (30–52 μmol kg^?1 h^?1) for creatinine, 0.02 % (0.05–0.08 μmol kg^?1 h^?1) for protein, 0.001 % (0.002–0.004 μmol kg^?1 h^?1) for urea, 0.5 % (0.64–3.6 μmol kg^?1 h^?1) for nitrite, and 0.5 % (0.0–6.9 μmol kg^?1 h^?1) for nitrate, and these proportions were not affected by water hardness or humic acid levels. The overall P excretion in R. quelen was 0.14–2.97 μmol kg^?1 h^?1. Ammonia excretion in R. quelen usually was significantly higher in the first 12 h after feeding, and no clear effect of water hardness, humic acid levels, and pH on this daily pattern of ammonia excretion could be observed. Water hardness only affected the ammonia and P excretion of R. quelen juveniles in the initial and fifth days after transfer, respectively. The exposure of this species to humic acid increased ammonia excretion after 10 days of exposure but did not affect P excretion. An increase in pH decreased ammonia and increased creatinine excretion but did not change P excretion in R. quelen. Therefore, when there is any change on humic acid levels or pH in the culture of this species, nitrogenous compounds must be monitored because their excretion rates are variable. On the other hand, P excretion rates determined in the present study are applicable to a wide range of fish culture conditions.     

Mortality,hematology, and histopathology of common snook Centropomus undecimalis (Perciformes: Centropomidae) exposed to acute toxicity of ammonia

This study aimed to evaluate the tolerance of common snook Centropomus undecimalis larvae and juveniles exposed to acute concentrations of un-ionized ammonia for 96 h at 35g L^?1 salinity, after 24 h starvation. For that, 10 larvae (20.85 ± 1.46 mm) of 47 days post hatch (DPH) per experimental unit (1.5 L) were exposed to 0.00 ± 0.00, 0.65 ± 0.04, 1.29 ± 0.09, 2.59 ± 0.18, 3.88 ± 0.27, 5.17 ± 0.34, and 6.47 ± 0.43 mg L^?1 NH₃, in triplicates, at 26.72 ± 0.08°C, dissolved oxygen at 5.72 ± 0.10 mg L^?1 and pH 8.45 ± 0.06. During this period, no mortalities were observed. Another trial was performed with five juveniles (20.35 ± 6.10 g, 13.90 ± 1.75 cm) per experimental unit (60 L) exposed to 0.00 ± 0.00, 2.26 ± 0.07, 2.68 ± 0.11, 3.20 ± 0.13, 3.68 ± 0.17, and 4.27 ± 0.16 mg L^?1 NH₃, in triplicates, at 21.90 ± 0.76°C, dissolved oxygen at 6.27 ± 0.21 mg L^?1 and pH at 8.38 ± 0.04. Fish mortality increased as ammonia concentrations increased at each day, and LC₅₀ 96 h was 3.52 mg L^?1 NH₃. Larvae were less sensitive than juveniles, demonstrating that the environmental toxicity of ammonia to common snook is influenced by age. Sublethal exposition to ammonia caused histological damages in gills of common snook juveniles and variation on glucose levels, hematocrit, and red blood cells number, showing negative effects on fish homeostasis. Moreover, compared to other species, the common snook has great resistance to ammonia.     

Effects of salinity and temperature during incubation on hatching and development of lingcod Ophiodon elongatus Girard, embryos

The interactive effects of salinity and temperature on development and hatching success of lingcod, Ophiodon elongatus Girard, were studied by incubating eggs at four temperatures (6, 9, 12 and 15°C) and five salinities (15, 20, 25, 30 and 35 g L^?1). Hatch did not occur in any of the 15°C treatments. Degree days (°C days) to first hatch was not influenced by temperature or salinity, however, calendar days to first hatch differed significantly for temperature (P<0.0001, 61±1, 44±1 and 35±1 days for 6, 9 and 12°C respectively). Degree days to 50% (427.1±4.2) hatch was not significantly influenced by temperature but was by salinity (P=0.0324). Viable hatch (live with no deformities, 74.1±4.0%) was greatest at 9°C and 25 g L^?1 but not significantly different in the range of 20–30 g L^?1. Larval length (9.4±0.13 mm) was greatest at 9°C and 20–30 g L^?1. Temperature and salinity significantly influenced all categories of deformities with treatments at the upper (12°C and 35 g L^?1) and lower limits (6°C and 15 g L^?1) producing the greatest deformities. The optimal temperature and salinity for incubating Puget Sound lingcod eggs was found to be 9°C and 20–30 g L^?1.     

Effect of salinity on survival, growth, oxygen consumption and ammonia-N excretion of juvenile whiteleg shrimp, Litopenaeus vannamei

In this study, we tested the lower salinity tolerance of juvenile shrimps (Litopenaeus vannamei) at a relatively low temperature (20 °C). In the first of two laboratory experiments, we first abruptly transferred shrimps (6.91 ± 0.05 g wet weight, mean ± SE) from the rearing salinity (35 000 mg L^?1) to salinities of 5000, 15 000, 25 000, 35 000 (control) and 40 000 mg L^?1 at 20 °C. The survival of L. vannamei juvenile was not affected by salinities from 15 000 to 40 000 mg L^?1 during the 96‐h exposure periods. Shrimps exposed to 5000 mg L^?1 were significantly affected by salinity, with a survival of 12.5% after 96 h. The 24‐, 48‐ and 96‐h lethal salinity for 50% (LS₅₀) were 7020, 8510 and 9540 mg L^?1 respectively. In the second experiment, shrimps (5.47 ± 0.09 g wet weight, mean ± SE) were acclimatized to the different salinity levels (5000, 15 000, 25 000, 35 000 and 40 000 mg L^?1) and then maintained for 30 days at 20 °C. Results showed that the survival was significantly lower at 5000 mg L^?1 than at other salinity levels, but the final wet weight under 5000 mg L^?1 treatment was significantly higher than those under other treatments (P<0.05). Feed intake (FI) of shrimp under 5000 mg L^?1 was significantly lower than those of shrimp under 150 00–40 000 mg L^?1; food conversion efficiency (FCE), however, showed a contrasting change (P<0.05). Furthermore, salinity significantly influenced the oxygen consumption rates, ammonia‐N excretion rates and the O/N ratio of test shrimps (P<0.05). The results obtained in our work provide evidence that L. vannamei juveniles have limited capacity to tolerate salinities <10 000 mg L^?1 at a relatively low temperature (20 °C). Results also show that L. vannamei juvenile can recover from the abrupt salinity change between 15 000 and 40 000 mg L^?1 within 24 h.     

Kinetics of Total Volatile Basic Nitrogen and Trimethylamine Formation in Stored Rohu (Labeo rohita) Fish

Fish freshness estimation has been mostly studied in terms of total volatile basic nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) determination and partially addresses the kinetics, which limits its practical utility. In this study, TVB-N and TMA-N content of Rohu stored under limited refrigerated (5 and 0°C) and frozen (?5°C) conditions for 42 days showed an increasing trend, respectively. TVB-N and TMA-N formation in stored Rohu was higher at higher temperature and their initial and final values were found 4.57 ± 0.321, 0.14 ± 0.047 mg/100g and 46.56 ± 0.994, 3.24 ± 0.112 mg/100g, respectively. The volatile formations in Rohu at ?5°C were slow, as the frozen storage arrests the enzymatic and microbial activities in comparison to 0°C and above. The kinetics of TVB-N and TMA-N were investigated using zero, first, and nth-order reaction model. First-order kinetics exhibited the best fit model for TVB-N (R² = 0.98; χ² = 0.045), whereas TMA-N formation showed nth-order kinetics (n = ?0.4608, R² = 0.96, χ² = 0.028) as best fit model. The first-order kinetic reaction contributed activation energy of 58.16 kJ/mol for TVB-N and 10.86 kJ/mol for TMA-N. TVB-N and TMA-N formations were influenced by storage temperature and duration as expected. Kinetic parameters were also significantly (P ≤ 0.05) affected by storage temperatures.     

Incubation of European Squid (Loligo vulgaris Lamarck, 1798) eggs at different salinities

Loligo vulgaris is a commercially important squid throughout the Mediterranean region and is a candidate species in biomedical and aquaculture research. Some loligo species (L. opalescens, L. forbesi, Sepiteuthis lessoniana) have now been cultured through some successive generations in closed, recirculating seawater systems. The effects of salinity on hatching European Squid (L. vulgaris Lamarck, 1798) eggs were investigated during November 2004. The egg capsules were incubated directly in salinity of 32, 34, 36, 38, 40, 42 and 37 g L^?1 (control group) at 19.8°C (SD 1.2°C), and a photoperiodicity of 12 h light:12 h dark for 16–23 days before hatching. In all treatments, the eggs were developed and hatched normally after 16–22 days at 32 g L^?1, 17–22 days at 34, 18–21 days at 42 g L^?1, 18–22 days at 36 and 40 g L^?1, 19–22 days at 37 g L^?1 and 19–23 h at 38 g L^?1. In the experiments, the highest hatching rate and hatching success (HS) of the eggs were obtained at 38 g L^?1 (hatching rate: 100% (SD 0%) and HS: 96.7% (SD 3.5%)) and the lowest hatching rate at 42 g L^?1 (hatching rate: 3% (SD 6%) and HS: 0%). Dorsal mantle lengths (DML) of new hatchlings ranged from 2.08 to 2.80 mm. The present study showed that salinity affects the hatching rate and HS of eggs and first hatching time and DML of paralarvae in L. vulgaris. The squid eggs at stage 11 (I) can tolerate 5 g L^?1 reduction and 3 g L^?1 increase in salinity.     

Optimization of blue mussel (Mytilus edulis) seed culture using recirculation aquaculture systems

By introducing recirculation aquaculture systems (RAS) in the nursery phase of the blue mussel (Mytilus edulis) (17–18 mm), we aimed at a similar growth and survival and a similar water quality compared to the commonly used flow‐through systems (FTS). To calculate water flow and size of the biofilter, a series of experiments were done to determine clearance rate (9.26 mL min^?1), pseudo faeces threshold (60 000 cells Pavlova lutheri mL^?1), nitrogen production (0.00065 mg TAN h^?1 ind^?1 and 1.6 × 10^?5 mg NO₂–N h^?1 ind^?1) and oxygen consumption (0.03 ± 0.01 mg O₂ h^?1 ind^?1). RAS showed no significant differences in water quality (0.06 mg TAN L^?1; 7.7 mg O₂ L^?1) and growth performance of mussel seed specific growth rate (SGR = 5% day^?1) after the experimental period of 4 weeks compared with FTS. The low water refreshment, 10% per day, as well as the constant chlorophyll concentrations (9.76 ± 1.06 μg L^?1), suggests the potential of RAS as culture system for mussel seed.     

Pharmacokinetic/pharmacodynamic properties and P‐glycoprotein expression in pacific white shrimp,Litopenaeus vannamei after oral administration at three dosages of oxolinic acid

The experiments explored the pharmacokinetics (PK) properties of oxolinic acid (OXA) after oral administration at three dosages (10, 30 and 80 mg/kg) via medicated feed in the shrimp. The results showed that the C_max values of 4.31, 14.93 and 16.62 mg/L and AUC_0–∞ values of 92.61, 252.30 and 364.27 mg hr^?1 L^?1 were observed at three OXA dosage groups in the haemolymph respectively. In the hepatopancreas, C_max values of 7.90, 27.23 and 60.51 mg/kg and AUC_0–∞ values of 42.01, 133.06 and 219.06 mg hr^?1 L^?1 were observed at 0.5 hr post administration respectively. In the muscle, C_max values of 1.62, 5.80 and 7.36 mg/kg and the AUC_0–∞ values of 25.64, 98.10 and 134.24 mg hr^?1 L^?1 were observed at 2 hr post administration respectively. In the gills, C_max values of 2.87, 8.08 and 12.12 mg/kg and the AUC_0–∞ values of 51.38, 118.65 and 206.48 mg hr^?1 L^?1 were observed at 4 hr post administration respectively. In addition, the in vitro MIC values of OXA at three dosages against 132 strains of Vibrio were examined and showed that the minimum inhibitory concentration (MIC) values for OXA primarily ranged from 0.15–1.25 µg/ml, including eight strains of Vibrio showing MIC values ≥5 µg/ml. The MIC₅₀ and MIC₉₀ values of 132 strains were 0.62 and 1.25 μg/ml respectively. The AUC_0–24/MIC₉₀ ratios of Vibrio were 140.4 in 30 mg/kg group. Furthermore, the P‐glycoprotein (P‐gp) expression was determined in shrimp tissues after administration to three dosage groups (10, 30 and 80 mg/kg). The results showed that P‐gp expression was up‐regulated in the hepatopancreas (5.36‐, 13.68‐ and 31.06‐fold respectively) compared with the control group.     

Ionic manipulation of inland saline groundwater for enhancing survival and growth of Penaeus monodon (Fabricius)

A series of four trials were conducted on inland saline groundwater of 58 g L^?1 diluted to lower salinities up to 10 g L^?1 and later manipulating its ionic concentrations to enhance the survival and growth of Penaeus monodon postlarvae (PL). In the first experiment, the survival of PL was tested at several salinities (10, 20, 30, 40, 50 and 58 g L^?1), and the survival of PL was studied in comparison with natural sea water of similar salinities. Complete mortality of PL was observed at all salinity levels within 144 h. Longest survival for 96 h followed by 72 h was found at 10 and 20 g L^?1 salinity respectively. In the second experiment, survival of PL was tested at 10–20 g L^?1 salinity at different concentrations of calcium varying between 100 and 300 mg L^?1. The survival of PL could be increased to 7 days at 12.5 g L^?1 salinity by reducing the calcium level to 200 from 921.8 mg L^?1 with magnesium and potassium levels of 208.5 and 30.03 mg L^?1 respectively. In the third experiment, the survival of PL could be further enhanced to 18 days at the same salinity by increasing the magnesium level from 208.5 to 400 mg L^?1 with potassium held at 30.03 mg L^?1. Survival and growth of PL in inland saline water of 12.5 g L^?1 salinity similar to performance in sea water of the same salinity was achieved by increasing the potassium concentration from 30.03 to 200 mg L^?1 with calcium and magnesium levels of 199.5 and 199.4 mg L^?1 respectively.     

Contribution of microorganisms to the biofilm nutritional quality: protein and lipid contents

The nutritional quality of biofilm, a microbial community associated to an organic matrix, was evaluated in artificial substrate (polyethylene screen) in net cages during 30 days in the Patos Lagoon estuary, Southern Brazil. During this period, samples of biofilm were collected each 5 days for analysis of chlorophyll a, microorganisms abundance, dry weight, protein and lipid contents. During the study, chlorophyll a varied from 0.38 to 2.75 μg cm^?2; dry weight between 7.16 and 17.63 mg cm^?2; protein content from 0.43 to 1.76 mg cm^?2 and lipid concentration between 1.21 and 4.23 mg cm^?2. The variation of lipid in the biofilm was closely related to the abundance of free heterotrophic bacteria (34.25–56.54 × 10⁶ cells cm^?2), filamentous cyanobacteria (7.5–15.9 × 10⁶ filaments cm^?2), flagellates (6.92–12.89 × 10⁶ cells cm^?2) and mainly nematodes (29–1,414 organisms cm^?2), while protein content varied similarly to the abundance of unicellular centric diatoms (52.10–179.81 × 10³ cells cm^?2), and nematodes. This information will allow a better management of food supply to raised aquatic organism with the utilization of natural productivity in the culture systems, with considerable decrease in production costs.     

Use of formalin and copper to control ichthyophthiriosis in the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell)

Infestations of the protozoan parasite, Ichthyophthirius multifiliis, cause the serious disease ichthyophthiriosis in freshwater fish throughout the world. Formalin is a recommended treatment for ichthyophthiriosis in the Australian fish silver perch (Bidyanus bidyanus Mitchell), but the disease is difficult to control in ponds, particularly at low water temperatures. Experiments were carried out to develop an improved treatment regime for formalin and to evaluate copper as a therapeutant. Silver perch fingerlings infested with I. multifiliis were stocked into 55 L aquaria at temperatures of 14.8–17.6 °C and alkalinities of 70–110 mg L^?1. Formalin (34–38% formaldehyde) or copper (24.5% copper sulphate) were added to the aquaria and then monitored and readjusted to nominal concentrations daily. A concentration of 30 mg L^?1 formalin controlled ichthyophthiriosis, but fish treated with 20 mg L^?1 remained infested with theronts and trophonts on day 17; survival at both concentrations was 100%. A concentration of 10 mg L^?1 formalin did not control ichthyophthiriosis and all fish were dead from the infestation by day 17. Fish treated with 0.1 or 0.2 mg L^?1 copper were free of theronts and trophonts by days 17 and 14, respectively, and survival was 100%. Survival at 0.05 mg L^?1 copper was 100%, but fish remained infested. At 0.25 mg L^?1 copper, survival was 82.5% and there were no theronts or trophonts on gill and skin tissues of fingerlings by day 14. There was total mortality of fish treated with 0.5 or 1.0 mg L^?1 copper suggesting these concentrations are toxic to silver perch. All fish in infested‐control treatments died. In earthen ponds containing silver perch, 0.2 mg L^?1 copper was depleted to below 0.1 mg L^?1 within 24 h, and concentrations of 25–38 mg L^?1 formalin were depleted to below 15 mg L^?1 within 48 h. Treatment regimes involving daily applications of formalin or copper controlled ichthyophthiriosis in silver perch in earthen ponds at costs of $US466.37 and $US65.58 hectare^?1 day^?1 respectively. This study has developed a new formalin‐treatment regime for the control of ichthyophthiriosis, and demonstrated that copper sulphate is a potential therapeutant for this serious disease of silver perch.     

Effectiveness of eugenol sedation to reduce the metabolic rates of cool and warm water fish at high loading densities

Effects of eugenol (AQUI‐S^®20E, 10% active eugenol) sedation on cool water, yellow perch Perca flavescens (Mitchill), and warm water, Nile tilapia Oreochromis niloticus L. fish metabolic rates were assessed. Both species were exposed to 0, 10, 20 and 30 mg L^?1 eugenol using static respirometry. In 17°C water and loading densities of 60, 120 and 240 g L^?1, yellow perch controls (0 mg L^?1 eugenol) had metabolic rates of 329.6–400.0 mg O₂ kg^?1 h^?1, while yellow perch exposed to 20 and 30 mg L^?1 eugenol had significantly reduced metabolic rates of 258.4–325.6 and 189.1–271.0 mg O₂ kg^?1 h^?1 respectively. Nile tilapia exposed to 30 mg L^?1 eugenol had a significantly reduced metabolic rate (424.5 ± 42.3 mg O₂ kg^?1 h^?1) relative to the 0 mg L^?1 eugenol control (546.6 ± 53.5 mg O₂ kg^?1 h^?1) at a loading density of 120 g L^?1 in 22°C water. No significant differences in metabolic rates for Nile tilapia were found at 240 or 360 g L^?1 loading densities when exposed to eugenol. Results suggest that eugenol sedation may benefit yellow perch welfare at high densities (e.g. live transport) due to a reduction in metabolic rates, while further research is needed to assess the benefits of eugenol sedation on Nile tilapia at high loading densities.     

Growth of juvenile common snook (Centropomus undecimalis Bloch, 1792) reared at different temperatures and salinities: Morphometric parameters,RNA/DNA,and protein/DNA ratios

We investigated the growth of juvenile common snook (Centropomus undecimalis) reared at 25°C and 28°C and salinities of 0.3, 15, and 32 g L^?1. Total length, weight, RNA/DNA, and protein/DNA ratios were determined after 90 days of experiment. Higher growth was observed at 28ºC compared with 25°C, at the same salinity. At 28°C and 15 g L^?1 salinity, the weight (25.14 g) of juveniles was twice that of the juveniles reared at the lower temperature. At different salinities, only higher temperature affected growth, with higher weight values obtained at 15 g L^?1 in comparison with 0.3 and 32 g L^?1. Length was similar at 0.3 and 15 g L^?1. The RNA/DNA ratio was greater in juveniles reared at a salinity of 15 g L^?1 when compared with 0.3 and 32 g L^?1. This study shows that the combination of higher temperature and intermediate salinity promotes better growth of common snook juveniles.