Comparative effectiveness of 2-phenoxyethanol and Propiscin as anesthetics for juvenile sea bass <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> L.

The comparative effectiveness of 2-phenoxyethanol and Propiscin as anesthetics were studied on juvenile sea bass. Both anesthetics showed low toxicity and good hypnotic characteristics, however median survival times at the same concentration of both anesthetics differed. Propiscin showed much lower LT₅₀ than 2-phenoxyethanol, pointing towards its elevated toxicity in juvenile sea bass, even the same concentrations of Propiscin induced slower anesthesia than 2-phenoxyethanol. The most suitable Propiscin concentration for anesthesia was 0.56 ml/l, while the most suitable concentration of 2-phenoxyethanol was 0.32 ml/l for juvenile sea bass. Mortalities after 96 h were induced with Propiscin at lower concentrations then of 2-phenoxyethanol, resulting in the conclusion that the 2-phenoxyethanol is a safer anesthetic for use with juvenile sea bass (Dicentrarchus labrax L.).     

Physiological responses of great sturgeon (Huso huso) to different concentrations of 2-phenoxyethanol as an anesthetic

The objective of the study was to evaluate the efficacy of 2-phenoxyethanol (2-PE) as an anesthetic in great sturgeon under two experiments. First, fish were exposed to 0.1, 0.3, 0.5, 0.7 and 0.9?mL/L 2-PE, and time to induction (deep anesthesia) and recovery from anesthesia were measured. At concentration of 0.1?mL/L, 2-PE failed to induce deep anesthesia in fish, whereas at concentrations of 0.7 and 0.9?mL/L, all the fish were anaesthetized within 3?min of exposure. For assessing the impact of effective concentrations of 2-PE on physiological responses of great sturgeon, hematological indices, plasma metabolites, electrolytes, enzymes and cortisol levels were measured. The use of 2-PE induces a significant increase in RBC values at 0.3?mL/L concentration and a parallel increase in hemoglobin and hematocrit values. 2-PE anesthesia had no effect on WBC, MCV, MCH and MCHC levels when compared to control group. Serum glucose, cholesterol and cortisol levels were significantly high in 0.3 and 0.5?mL/L 2-PE. Moreover, AST levels were increased in fish exposed to the 0.3?mL/L 2-PE comparing with the control group (P?<?0.05). There were no significant differences in serum levels of total protein, triglycerides, ALP, ALT, Cl^?, Na⁺, K⁺, Ca²⁺ and Mg²⁺. In this study, alteration in hematological and serum biochemical indices was time-dependent. This study demonstrates that rapid induction of deep anesthesia with a relatively high concentration of 2-PE (0.7 and 0.9?mL/L) was associated with the lowest effects on the hematological and serum biochemical indices in great sturgeon and therefore would be recommended as eligible doses for hematological studies in this species.     

The effects of surgically implanted dummy tags on the survival,growth performance,and physiology of pikeperch (<Emphasis Type="Italic">Sander lucioperca</Emphasis>)

The aim of this work was to determine the impact of surgically implanted telemetry transmitters (TTs) on the growth, survival, hematological and biochemical indexes, and wound healing in juvenile pikeperch (Sander lucioperca) (body weight 60–90 g). Two incision suturing methods were used—silk sutures (experiment I—group ST) or tissue adhesive (experiment II—group GT). After tagging, the fish were held in a recirculating system for 35 days. No statistically significant differences were noted in the growth or condition indexes analyzed among the fish tagged with TT compared with those from the control groups (untagged). Substantial individual variability was noted, however, in the parameters examined in both the control and tagged groups. Among the hematological indexes, statistically significant differences were only noted in experiment I. Lower values of mean corpuscular volume and mean corpuscular hemoglobin were noted in group ST. Among the biochemical parameters, creatinine was statistically significantly threefold lower, magnesium and alkaline phosphatase (ALP) levels were lower, and ammonia levels were higher in group ST than in the control group. In experiment II, significant differences were only noted for ALP. Tissue adhesive was the superior and more effective method for closing the incision after TT implantation in juvenile pikeperch. This type of suturing facilitated faster healing, and it had less of an impact on juvenile pikeperch welfare.     

Comparison of the effects of four anaesthetics on biochemical blood profiles of perch

This study investigated the feasibility of using clove oil, 2-phenoxyethanol, or Propiscin as an alternative to tricaine methane sulphonate (MS 222) as a fish anaesthetic, particularly in regard to reducing fish stress. The biochemical blood profiles of perch Perca fluviatilis L. anaesthetized with either MS 222 (100 mg L⁻¹), clove oil (33 mg L⁻¹), 2-phenoxyethanol (0.40 mL L⁻¹) or Propiscin (1.0 mL L⁻¹), and a non-anaesthetized control group were compared. Biochemical profiles were determined from blood samples collected before treatment in controls. For each anaesthetic tested, fish were divided into two groups, one sampled immediately after 10-min anaesthesia and a second, sampled 24 h after 10-min anaesthesia. The values determined in the present study suggested that internal organs and tissues of perch were slightly altered by MS 222, clove oil and 2-phenoxyethanol anaesthesia, but not by Propiscin anaesthesia.     

Using enriched stable isotopes of barium and magnesium to batch mark otoliths of larval golden perch (Macquaria ambigua,Richardson)

Woodcock SH, Gillanders BM, Munro AR, McGovern F, Crook DA, Sanger AC. Using enriched stable isotopes of barium and magnesium to batch mark otoliths of larval golden perch (Macquaria ambigua, Richardson). Ecology of Freshwater Fish 2011: 20: 157–165. © 2010 John Wiley & Sons A/S Abstract – Enriched stable isotope immersion techniques were used to mark the otoliths of larval golden perch (Macquaria ambigua) immediately post‐hatch. Two experiments were undertaken: the first involved rearing larvae in water enriched with three concentrations of ¹³⁷Ba for 1–5 days. Marks were produced in as little as 1 day; however, otolith isotope ratios reached equilibrium with the water in 5 days at 90 μg·l^?1. The second experiment involved rearing larvae in isotope enriched water with combinations of stable isotopes of Ba and Mg for 4 days after hatching. Seven significantly different isotopic signatures were produced using three Ba isotopes, which were reflective of the water. Only slight differences were found in otoliths of larvae that were reared in combinations of Mg isotopes, which did not reflect the water chemistry. The length of golden perch at 3 weeks of age showed that isotope immersion did not negatively affect early growth.     

Size‐related oxygen consumption and ammonia excretion of Eurasian perch (Perca fluviatilis L.) reared in a recirculating system

Oxygen consumption (OC) and ammonia excretion rates (AE) of perch were measured under commercial‐like conditions (temperature 23.3 °C) in both fed (F) and feed‐deprived groups (D). Measurements were taken in triplicate in six sized batches of perch ranging from 44.8 to 336.2 g. The mean daily OC was 288.3–180.6 mg O₂ kg^?1 h^?1 for group F fish ranging in size from 44.8 to 279.4 g body weight. The mean daily AE expressed as total ammonia nitrogen (TAN) was 13.8–5.2 mg TAN kg^?1 h^?1 in the same groups. Daily peaks of OC in group F perch were observed 6 h after the onset of feeding for each size group with relatively stable values up to the end of feeding. Peaks of daily AE in group F perch were observed 10 h after the onset of feeding in each size group, with a rapid decrease up to 16 h after onset. In group D, OC was 181.1–110.5 mg O₂ kg^?1 h^?1 in the weight range 57.9–336.2 g. The daily mean AE was 1.7–0.5 TAN kg^?1 h^?1 in this group. No dramatic peaks of OC and AE were observed in group D perch.     

A wide difference in susceptibility to nitrite between Eurasian perch (Perca fluviatilis L.) and largemouth bass (Micropterus salmoides Lac.)

Influence of nitrite on two fish species, Eurasian perch (Perca fluviatilis L.) and largemouth bass (Micropterus salmoides Lacépède), was assessed in two acute toxicity tests. In the first one, lethal concentrations (48hLC50) of nitrite were estimated at 11 mg l^?1 NO₂ ^? for perch and 882 mg l^?1 NO₂ ^? for bass. In the second test, fishes were exposed for 48 h to concentrations representing ¼ and ½ value of 48hLC50 for each species. This test showed that the higher nitrite concentration in the water the higher methaemoglobin content in the blood, and nitrite levels in the blood plasma were observed in both species. On the other hand, leucocyte count showed opposite trend. Activity of NADH-methaemoglobin reductase was markedly lower in largemouth bass compared to Eurasian perch and was stimulated by nitrite exposure in neither of the species.     

Anesthetic activity of the essential oil of Aloysia triphylla and effectiveness in reducing stress during transport of albino and gray strains of silver catfish,Rhamdia quelen

This study investigated the efficacy of the essential oil (EO) of Aloysia triphylla as an anesthetic for albino and gray strains of silver catfish, Rhamdia quelen. Juveniles were exposed to concentrations between 20 and 800 μL L^?1 EO of A. triphylla to evaluate time of induction and recovery from anesthesia. In another experiment, both strains were divided into four groups such as 0 (control), 30, 40, or 50 μL L^?1 EO and transported for 5 h. The longest time for anesthetic induction and recovery was observed in the albinos. Both strains reached anesthesia in the 100–800 μL L^?1 (11.1–1.24 min) range, without mortality, being 200 μL L^?1 the best response considering time to anesthesia (5.35 min). Albinos transported with all EO concentrations showed higher values of carbon dioxide in the water of transport, but lower levels were observed in grays transported with 40 and 50 μL L^?1 EO when compared to control fish. The same concentrations did not prevent significant whole-body cortisol rise at the end of transport in the albino strain. Juveniles of both strains transported with EO presented lower ion loss to the water compared to control fish. The EO of A. triphylla is an effective anesthetic for albino and gray silver catfish. This EO increases whole-body cortisol levels in the albino strain, but as it reduces net ion loss as in the gray strain, it can be also recommended for transport.     

Carbohydrate utilization by juvenile silver perch, Bidyanus bidyanus (Mitchell). I. Uptake and clearance of monosaccharides following intraperitoneal injection

Abstract Intraperitoneal carbohydrate tolerance tests were done to assess the ability of silver perch, Bidyanus bidyanus, to utilize the predominant monosaccharides in plant ingredients currently being used in the formulation of aquaculture feeds for this species. Preliminary experiments carried out to assess baseline plasma glucose concentrations indicated that blood glucose levels were elevated within 2 min of handling and silver perch required a period of 48 h without feeding before plasma glucose levels remained constant. In the first carbohydrate test, either glucose, galactose or xylose were administered by injection into the intraperitoneal cavity at a dose rate of 1 g carbohydrate kg^?1 body weight (BW). In the second carbohydrate test, glucose was administered at a dose rate of either 2 or 4 g glucose kg BW^?1. Following injection, uptake and clearance rate of the carbohydrates from the blood stream was monitored over a 24‐h period. Silver perch were significantly more efficient at the uptake and clearance of glucose from the blood stream than xylose or galactose. Maximum plasma glucose concentrations (22.2 mmol L ^?1) were recorded at 1 h following injection and basal levels (3.44 mm ) were attained between 6 and 12 h following injection. For both galactose and xylose, maximum concentrations were recorded at 1 and 3 h, respectively, and concentrations of both monosaccharides remained significantly elevated 24 h after the administration. Plasma glucose concentrations of silver perch administered with either 2 or 4 g glucose kg BW^?1 were significantly elevated and peaked at similar levels (30.2 mmol L ^?1 and 30.7 mmol L ^?1 respectively) 3 h after injection. Basal plasma glucose concentrations were attained in silver perch injected with 2 g glucose kg BW^?1 at 24 h following administration. Plasma glucose concentrations remained significantly elevated in fish injected with 4 g glucose kg BW^?1 after 24 h. These findings indicate that silver perch are more efficient at utilizing glucose than either xylose or galactose, and that there are also differing maximum threshold for the inclusion of ingredients rich in glucose, galactose and xylose into the diets of silver perch.     

Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post‐hatching (DPH) larvae were exposed to a single immersion treatment in 17α‐methyltestosterone (MT), 17α‐methyldihydrotestosterone (MDHT) or 17α‐ethynyltestosterone (ET) at 200, 600 and 1800 μg L^?1 over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 μg L^?1) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi‐square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 μg L^?1 (86.0%, 90.0% and 86.7% respectively). At 200 μg L^?1 none of the androgens altered sex ratio. At 600 μg L^?1, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 μg L^?1) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two‐immersion treatments significantly increased the proportion of males in the MT‐treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET‐treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 μg L^?1) was not significantly different.     

Effect of stocking density on survival and growth performance of pikeperch, <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.), larvae under controlled conditions

The effect of stocking density on the survival and growth of pikeperch, Sander lucioperca (L.), larvae was examined in two consecutive experiments. In experiment I, 4-day-old larvae [body wet weight (BW): 0.5 mg; total body length (TL): 5.6 mm] were reared in 200-l cylindro-conical tanks in a closed, recirculating system (20 ± 0.5°C) at three stocking densities (25, 50 and 100 larvae l⁻¹) and fed a mixed feed (Artemia nauplii and Lansy A2 artificial feed) for 14 consecutive days. At densities of 25 and 100 larvae l⁻¹, growth rate and survival ranged from 2.7 to 1.9 mg day⁻¹ and from 79.2 to 72.3%, and fish biomass gain ranged from 0.6 to 2.0 g l⁻¹, respectively. There were two periods of increased larval mortality: the first was at beginning of exogenous feeding and the second during swim bladder inflation. In experiment II, 18-day-old larvae (BW: 35 mg; TL: 15.6 mm) obtained from experiment I were reared under culture conditions similar to those of experiment I, but at lower stocking densities (6, 10 and 15 larvae l⁻¹). The fish were fed exclusively with artificial feed (trout starter) for 21 consecutive days. At densities of 6 and 15 larvae l⁻¹, the growth rate and fish biomass gain ranged from 28.8 to 23.1 mg day⁻¹ and from 2.0 to 3.3 g l⁻¹, respectively. The highest survival (56.5%) was achieved at a density of 6 larvae l⁻¹. Mortality at all densities was mainly caused by cannibalism II type behaviour (27–35% of total). In both experiments, growth and survival were negatively correlated and fish biomass gain positively correlated with stocking densities. The present study suggests that the initial stocking density of pikeperch larvae reared in a recirculating system can be 100 individuals l⁻¹ for the 4- to 18-day period post-hatch and 15 individuals l⁻¹ for the post-19-day period.     

Effects of ascorbic acid enrichment by immersion of rainbow trout (Oncorhynchus mykiss, Walbaum 1792) eggs and embryos

This study was conducted to examine the effects of different forms and concentrations of ascorbic acid (vitamin C), and different enrichment times (24 and 48 h post ovulation) on egg, embryo and alevin ascorbate concentrations and survival of rainbow trout (enrichment was at the ova stage). In experiments 1 and 2, fertilized eggs were immersed in water containing ascorbate at 0 (control), 100, 1000 mg L^?1 l ‐ascorbic acid (AA) and 2000 mg L^?1 l ‐ascorbyl monophosphate (AP). In experiment 3, 0 (control), 500 and 1000 mg L^?1 AA neutralized (N) with NaOH, 1000 mg L^?1 AA non‐neutralized (NN), 1000 and 2000 mg L^?1 AP immersions were used. The mean total ascorbic acid (TAA) and dehydroascorbic acid (DHA) concentrations were measured before fertilization, at 3 and 24 h after fertilization, at the eyed stage, and in hatched alevins. We observed significant differences in TAA concentration at different immersion levels at 3 and 24 h after fertilization. Survival decreased significantly depending on the level of vitamin C, pH of the solutions and immersion time. We suggest that when broodstock rainbow trout do not have enough vitamin C in their ovaries, immersion of eggs in 1000 mg L^?1 of neutralized AA may be useful.     

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.     

Carbohydrate utilization by juvenile silver perch,Bidyanus bidyanus (Mitchell). IV. Can dietary enzymes increase digestible energy from wheat starch,wheat and dehulled lupin?

The effects of exogenous digestive enzyme supplements on the digestibility of wheat starch or diets containing either wheat or dehulled lupin (Lupinus angustifolius var. gungurra) by silver perch (Bidyanus bidyanus) were investigated. In the first experiment, Natustarch^® (α‐amylase supplement specific to starch) was added at three nominal concentrations (0, 50, 100 or 150 mg kg^?1 diet) to diets containing either raw or 100% gelatinized wheat starch (30% dietary inclusion content) and fed to silver perch. The apparent digestibility coefficients (ADCs) for dry matter, starch and energy were calculated. The action of Natustarch^® on the diet and in the digestive tract was also investigated. The addition of Natustarch^® to diets containing raw and gelatinized wheat starch led to an average increase in reducing sugar content of diets of 67% and 340% respectively, indicating that the α‐amylase was more efficient at hydrolysing wheat starch in the gelatinized form. Gelatinized wheat starch was digested more efficiently than raw wheat starch. However, although the addition of Natustarch^® at ≥ 50 mg kg^?1 led to a significant increase in digestibility of raw wheat starch; the digestibility of gelatinized wheat starch, which was already high, was not further improved. Leaching due to immersion in water caused a minor loss of α‐amylase activity from diet pellets treated with Natustarch^® (～ 13% after 5 min). The α‐amylase activity in the anterior section of the intestinal tract of silver perch fed diets containing Natustarch^® was not affected, indicating that the α‐amylase had been denatured by the acidic conditions in the stomach of silver perch. In the second experiment, diets containing wheat or lupin (at the 30% inclusion content) were treated with Natugrain‐blend^®[an enzyme supplement containing β‐glucanase and β‐xylanase, specific to non‐starch polysaccharides (NSPs)] at three nominal concentrations (0, 75, 150 or 300 μL kg^?1) and fed to silver perch. ADCs for energy and protein were calculated. The addition of Natugrain‐blend^® had no effect on dry matter, energy or protein digestibility of the diets or ingredients.     

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.     

Efficacy of formalin,iodine and sodium chloride in improvement of egg hatching rate and fry survival prior to the onset of exogenous feeding in yellow perch

Egg disinfection is considered the most important routine work in hatcheries to avoid fungal and/or bacterial infection of fish eggs. The aim of this study was to determine the effectiveness of three disinfectants: formalin, iodine and sodium chloride on the hatching success of yellow perch eggs. The disinfectants were tested in triplicate at different concentrations for 15 and 30 min bath treatments. Two experiments were conducted; formalin at five concentrations (25, 50, 100, 150 and 200 mg L^?1) and 25 mg L^?1 iodine were tested in the first experiment. The second experiment involved formalin at three concentrations (250, 500 and 1000 mg L^?1), iodine at three concentrations (50, 100 and 250 mg L^?1) and sodium chloride at three concentrations (500, 1000 and 3000 mg L^?1) were used. Iodine and sodium chloride‐treated eggs hatched earlier than formalin‐treated eggs. The highest mean percentage of eyed stage, hatching rate and survival to first feeding fry was observed at 200 mg L^?1 formalin for 30 min, 50 mg L^?1 iodine for 15 min and 500 mg L^?1 sodium chloride for 30 min. High concentrations of formalin (1000 mg L^?1), iodine (250 mg L^?1) and sodium chloride (1000 and 3000 mg L^?1) showed toxicity to yellow perch eggs, resulting in low hatching rate and survival to first feeding fry. We recommended formalin at a concentration of 150–200 mg L^?1 for 30 min as an effective, easily available and low‐cost disinfectant for routine use to improve yellow perch hatchability.     

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.     

Enzyme treatment for elimination of egg stickiness in tench (Tinca Tinca L.), European catfish (Silurus Glanis L.) and common carp (Cyprinus Carpio L.)

Enzyme treatment to eliminate egg stickiness in tench, European catfish and common carp was compared with standard methodology in an attempt to decrease time consuming under hatchery conditions. Eggs of tench and E. catfish were exposed to an alcalase enzyme MERCK EC 3.4.21.14 (0.6 AU g^?1) solution 3 min after egg fertilization for 2 min. The best enzyme concentration in tench and E. catfish was 10 and 20 ml l^?1 of enzyme, respectively. The eggs of c. carp were successfully destickiness with ALCALASE DX (2.5 AU g^?1) using two concentration of enzyme (2 ml l^?1 and 20 ml l^?1) from 8 to 20 min after fertilization.     

The use of formaldehyde for the disinfection of maternally incubated eggs of noble crayfish (<Emphasis Type="Italic">Astacus astacus</Emphasis>)

The high mortality of maternally incubated eggs represents a serious problem that prevents the development of noble crayfish (Astacus astacus) farming in Italy. In this experiment, formaldehyde bath technique has been tested with maternally incubating females. The survival rate of maternally incubated eggs, exposed to progressively reduced concentrations of formaldehyde (4000, 3000, 2000, 1000, 1500 and 500 mg l^?1), has been compared with that of untreated controls for two consecutive years (2010 and 2011). The formaldehyde treatments were administered as disinfection baths, for a period of 15 min, twice a week. A concentration of formaldehyde of 500 mg 1^?1, or greater, was found to be effective in controlling egg mortality, without apparent harming the female broods.     

Effect of light intensity,prey density,and ontogeny on foraging success and prey selection of larval yellow perch (Perca flavescens)

Light intensity has been shown to influence the foraging success of larval fish. However, the effect of light intensity on larval foraging is likely variable and influenced by both the density and characteristics of planktonic prey. In this study we examined the influence of light intensity of 0.1, 2.0, and 60 μmol·s^?1·m^?2 Photosynthetically Active Radiation (PAR) on foraging of yellow perch (Perca flavescens) larvae at two prey densities. We fed them with a mixture of zooplankton taxa common to lakes inhabited by yellow perch. In addition to light intensity and prey density, the effect of larval yellow perch size was examined by using fish ranging from 9 to 15 mm. The results of our study indicated that yellow perch larvae are well adapted to feed at a wide range of light intensities, as there was no difference in foraging success at investigated light intensities. Increasing prey density from 25 to 150 (zooplankton·l^?1) significantly improved the foraging success of larval yellow perch. However, the influence of prey density on foraging success was dependent on fish length. Improved foraging success at increased prey densities occurred only for individuals with a total length >10 mm. Overall, prey selection by fish larvae was influenced by light intensity, prey density, and fish length. However, the factors that influenced selection for specific prey types differed. Our study, combined with evidence from other field and laboratory work, highlight the need for a better understanding of the influence of prey density on foraging throughout ontogeny.