Isolation, partial characterization and localization of integumental peroxidase, a stress-related enzyme in the skin of a teleostean fish (Cyprinus carpio L.)

Biochemical and immunological characteristics of peroxidase activity of the skin epithelium of common carp (Cyprinus carpio) were investigated and compared with peroxidase activity of blood cells. Skin as well as blood-borne peroxidases eluted from the Superdex column as a 135 kDa protein and both probably are tetrameric molecules. Skin peroxidase activity was characterized by a V_max of 51.5 ± 1.3 U mg^-1 min^-1 and a K_M of 1.64 ± 0.18 mM ortho-phenylenediamine (OPD), whereas blood-borne peroxidase was characterized by a 1,000 fold higher specific activity (V_max = 30.5 103 ± 2.5 103 U mg^-1 min^-1) and a higher affinity (K_M = 0.875 ± 0.003 mM OPD). Polyclonal antibodies were raised against concanavalin-A purified skin peroxidase as well as blood-borne peroxidase. Immunocytochemical labelling showed that peroxidase is present in mucous cells and in mucus covering the skin and gill epithelia, as well as in erythrocytes and leucocytes. We conclude that the mucous cells of the skin produce a biochemically distinct peroxidase that is released in the mucus and may contribute to the antimicrobial properties of the mucous layer covering the skin. After exposure of the fish to cadmium the kinetic characteristics of the enzyme activity, as determined in skin homogenates, changed considerably. The V_max increased significantly to 61.9 ± 1.1 U mg^-1 min^-1, and the affinity for OPD increased to the value demonstrated for blood-borne peroxidase (K_M = 0.888 ± 0.045 mM OPD). Increased peroxidase levels after cadmium exposure were also demonstrated immunochemically in a dotblot assay. However, no significant changes were observed when the circulatory system of the fish was perfused prior to sampling, indicating that erythrocytes are a major contributor to the increased peroxidase activity in carp skin during cadmium exposure. This likely reflects the increased vascularization of the connective tissue layer underlying the skin epithelium, which takes place when the fish are exposed to chronic stressors including cadmium. In the cadmium-exposed fish this effect prevented the biochemical detection of stressor-related changes in epithelial peroxidase reported earlier with cytochemical methods.     

Grass carp (Ctenopharyngodon idella) grazing on duckweed (Spirodela polyrhiza)

The aims of this experiment were (1) toquantify the ability of grass carp to processduckweed and (2) to assess indirect changes inwater chemistry and phytoplankton community,caused by grass carp feeding. Yearling grass carp sized 126 ± 7.7 mm (TL) and19.6 g in weight were kept in 9 laminate tanksof 1 m³ for 14 days. Two stockingdensities (2 and 6 fish per m³) anda control without fish were used. Standard growthrate (SGR) of grass carp fed exclusively onduckweed was 0.70% body weight (BW) d^–1and food conversion ratio (FCR) reached 2.0(average water temperature =21.1 ± 3.8 °C). Daily food intakewas 0.2 g of duckweed dry weight (DW), i.e.,1% of average BW of grass carp. SGR ofduckweed growing in 20 × 20 cm floatingenclosures, differed significantly[F(6,2) = 417.9; p = 0.002] between the twostocking densities of grass carp and thecontrol tanks (without fish). Mean SGR ofduckweed was 0.02 g g^–1 day^–1 and thehighest SGR was recorded in the control tanks.Both decrease in NH₄-N and increase inNO₂-N concentrations differedsignificantly between the treatments[F(2,2) = 45.3; p = 0.02 and F(2,2) = 19.2; p = 0.04 respectively]. Changes in other nitrogenand phosphorus components (NO₃-N, TN, TPand PO₄-P) caused by stocking of grasscarp were not significant. Biomass ofphytoplankton, dominated by filamentous algaeand blue-greens, increased proportionately tostocking density of grass carp. Althoughduckweed has a large potential for nutrientremoval, the most common pathway for thenutrients released through grass carp grazingif duckweed cover is loose is theirincorporation into phytoplankton biomass.     

Effects of paraquat treatment on fish transaminase molecular subforms

The effects of paraquat (PQ; 1,1′-dimethyl-4,4′-bipyridylium dichloride) treatment were investigated in carp, silver carp and wels. The serum glutamic-oxalacetic transaminase (GOT; L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1.) level was enhanced by 50% at 1 ppm exposure and by 100% at 10 ppm exposure in all species, and there was a change in the distribution of the molecular subforms of GOT in the liver and heart. The activities of the individual subforms decreased with increasing PQ concentration or after a longer exposure. In some cases, one of the subforms was no longer present in the liver. An increased serum GOT activity, a decreased enzyme activity in different organs and the disappearance of molecular subform indicate tissue damage.     

A new technique of feeding, repeated sampling of blood and continuous collection of urine in white sturgeon

A new technique combining oesophageal intubation, dorsal aorta cannulation, and urinary catheterization was developed to monitor concentration of nutrients in the blood circulation and their metabolites in the urine of 1–2 kg white sturgeon, Acipenser transmontanus. Three experiments were conducted to assess the technique based on: (1) quantitative delivery of nutrients; (2) stress levels post-operation; and (3) monitoring of nutrients in the blood and metabolites in the urine. In Experiment 1, recovery of intubated Cr₂O₃ was 105±5% (mean ± SEM, n=3) 3 h after intubation. In Experiment 2, plasma cortisol and glucose concentrations returned to respective basal levels of 8.2±1.8 ng ml^–1 and 74± mg dl^–1 (n=9) 48 h post-operation. In Experiment 3, sturgeon intubated with 1 g kg^–1 body weight of glucose or dextrin at 48 h post-operation showed a significantly different (p<0.05) peak plasma glucose level of 139±4 and 100±5 mg dl^–1 (n=5), respectively, at 4 h. Urinary glucose excretion was 1.8±0.9 mg kg^–1 h^–1 (n=5) 4–8 h after intubation with glucose. Our results show that the new technique allows quantitative delivery of nutrients, repeated sampling of blood, and continuous collection of urine in white sturgeon with minimum stress.     

三种鲤对暴发性鱼病抗病力的差异

本文报道三种鲤对嗜水气单胞菌引起暴发性鱼病的抗病力试验结果。当菌液浓度为６．０×１０￣８ＣＦＵ／ｍｌ，采用１０￣０、１０￣（－１）、１０￣（－２）、１０￣（－３）四个稀释度、０．３ｍｌ／尾注射剂量时，建鲤、野鲤和镜鲤的半数致死量（ＬＤ＿（５０））分别为１０￣（－１．３７５）、１０￣（－０．９７６）、１０￣（－０．５６２）。这三种鲤的半数致死量差异显著（Ｆ＞Ｆ＿（０．０５））。从四个方面研究了抗病机理：白细胞吞噬功能和补体替代途径（Ｃ＿３旁路）杀菌能力，镜鲤较强于野鲤和建鲤，但无显著差异（Ｆ＜Ｆ０．０５）；红细胞Ｃ＿（３ｂ）受体花环率和补体总量（单位／ｍｌ），是建鲤＞野鲤＞镜鲤，差异极显著（Ｆ＞Ｆ０．０１）。本研究结果还表明建鲤的红细胞Ｃ＿（３ｂ）受体花环率和补体总量稍高，但对暴发性鱼病病原（嗜水气单胞菌）较易感染。以上结果证明，不同品系鲤鱼对暴发性鱼病有种内特异性。     

Retracted: Effectiveness of carp pituitary extract and luteinizing hormone releasing hormone analogue administration (by either injection or cholesterol pellet implantation) on spawning performance in female sturgeon,Huso huso

The effectiveness of common carp pituitary extract (CPE), luteinizing hormone releasing hormone analogue (LHRH‐A₂) injections and LHRH‐A₂ implants for spawning induction in female sturgeon, Huso huso was examined. In the first trial, fish were injected with 7% physiological saline (control), 50 mg kg^?1 CPE or LHRH‐A₂ at 3.5, 7, 8 or 10 μg kg^?1. In the second trial, fish were treated with LHRH‐A₂ cholesterol pellet implants containing 0, 3.5, 7, 8 and 10 μg kg^?1 LHRH‐A₂. Ovulated eggs were removed using a minimally invasive surgical technique and were artificially fertilized. Injection of CPE and LHRH‐A₂ at doses of 3.5, 7, 8 and 10 μg kg^?1 resulted in the number of ovulated fish more than LHRH‐A₂ implants (similar doses) or controls, although there was no significant difference at doses of 8 and 10 μg kg^?1 (P ≥ 0.05). The latency period of fish receiving CPE and LHRH‐A₂ injections was approximately 20 h, which was significantly lower than in fish receiving LHRH‐A₂ implants (P ≤ 0.05). Furthermore, there were no significant differences in rates of fertilization or hatching among the progeny produced in any of the treatment groups (P ≥ 0.05). In conclusion, the data from this study could be useful for artificial propagation of not‐fully‐matured females of H. huso at sturgeon hatcheries.     

Amino acid composition of edible parts of three-year-old experimental scaly crossbreds of common carp (Cyprinus carpio, Linnaeus 1758)

The aim of this study was to compare the amino acid (AA) composition of edible parts of three experimental groups of carp, i.e. a pure line of Přerov scaly carp (PS), a hybrid line of Přerov scaly carp and Northern mirror carp (PS × M72), and a hybrid line of Přerov scaly carp and Ropsha scaly carp (PS × ROP), with the quality of the edible parts of control hybrids of Hungarian and Northern mirror carp (M2 × M72) in harvest size (K₃). A comparison between the controls (M2 × M72) and experimental carp (PS, PS × M72, PS × ROP) showed that their muscle tissues contained the same amounts of 10 AA [essential amino acids (EAA): Thr, Val, Leu, Phe, Lys, His; non‐essential amino acids (NEAA): Asp, Gly, Ala, Tyr] of the 16 AA determined. Glu, Asp, Lys and Leu were the AA with the highest muscle concentrations. The total EAA_sum and NEAA_sum contents in the fastest‐growing PS × ROP hybrid, in spite of specific differences found (P<0.05: Arg, Met; P<0.01: Pro), were practically identical to those found in the control group of M2 × M72 mirror carp. PS × ROP hybrid female and male muscle tissues differed (P<0.05) only in Met and Ala levels. Hard roes of experimental female carp (PS, PS × M72, PS × ROP) contained the largest quantities of Glu and Val, and that of control female carp (M2 × M72) the largest quantities of Glu and Gly. Hard roes of PS × ROP hybrids contained the largest quantities (P<0.01) of EAA_sum (52.44±0.19%). Compared with hard roes, soft roes from all groups of carp contained more EAA_sum (PS × ROP: 55.03±0.26%). The two most abundant AA in soft roes were Lys and Arg. The most abundant AA in the hepatopancreas in all carp groups were Glu, Asp, Leu and Arg. Hepatopancreas EAA_sum levels in experimental carp (PS, PS × M72, PS × ROP) were significantly (P<0.05) lower than those in controls (M2 × M72).     

Influence of low concentrations of Trichlorfon on haematological parameters and brain acetylcholinesterase activity in common carp, Cyprinus carpio L.

Trichlorfon, an organophosphorus insecticide, is used in aquaculture to eliminate fish ectoparasites. The present study was aimed at evaluating the effects of low concentrations of Trichlorfon (0.25 and 0.50 mg L^?1 for 1 and 24 h) on selected haematological parameters and brain acetylcholinesterase (AChE) of subadults of common carp, Cyprinus carpio. Results showed that Trichlorfon had no significant effect on the survival and haematocrit values of the exposed fish. However, all fish exposed to Trichlorfon exhibited leucopenia coupled with lymphocytopenia. Upon transfer to clean water, leucopenia did not return to normal in seven days. Brain AChE activity of the fish exposed to Trichlorfon for 24 h was reduced by 55–57% compared with the controls and inhibition was not restored fully within seven days. Hence, precautions should be taken when even low concentrations of Trichlorfon are used in carp culture, especially for long‐term treatments.     

Substrate specificity of brain acetylcholinesterase and its sensitivity to carbamate insecticides in <Emphasis Type="Italic">Carassius auratus</Emphasis>

The substrate specificity of brain acetylcholinesterase (AChE) in adult Carassius auratus fish and its sensitivity to carbamate insecticides were investigated in vitro. The results showed that the order of four substrates hydrolyzed by brain AChE in C. auratus was acetylthiocholine iodide > β-methylthiocholine iodide > propionylthiocholine iodide > butyrylthiocholine iodide, and the maximum velocity (V _max) of AChE hydrolyzing acetylthiocholine iodide (ATCh) was the highest among the four substrates, and the V _max values were 0.067 and 0.082 mmol min⁻¹ mg⁻¹ for male and female fish respectively. But their Michaelis–Menten constants (K _m) were the lowest, only 0.071 and 0.072 mmol/l respectively. Compared with other carbamate insecticides, the sensitivity of brain AChE to carbofuran was the highest and the IC₅₀ values were 1.04 × 10⁻⁶ mol/l for females and 1.17 × 10⁻⁶ mol/l for males. The inhibitory tendencies of eserine, methomyl, and aldicarb to brain AChE were very similar, and the percentage inhibition increased with time at the concentration of 1 × 10⁻⁶ mol/l. The order of inhibition potential of the three inhibitors from the highest to the lowest was eserine, aldicarb, and methomyl.     

Optimization of stocking density of freshwater prawn Macrobrachium rosenbergii (de Man) in carp polyculture in Bangladesh

A study was conducted to optimize stocking density of freshwater prawn, Macrobrachium rosenbergii, in carp polyculture for 3 months in 10 experimental ponds of 80 m². Five stocking densities of prawn, 2500, 5000, 7500, 10 000 and 12 500 ha^?1, were assigned to treatments T₁, T₂, T₃, T₄ and T₅ respectively. The densities of catla, Catla catla, rohu, Labeo rohita and silver carp, Hypophthalmicthys molitrix, were 2500, 5000, and 2500 ha^?1, respectively, in each treatment. Each treatment had two replicate ponds. The mean initial weights of prawn, catla, rohu and silver carp were 1.1±0.02, 8.28±0.1, 25.2±1.1 and 36.32±1.2 g respectively. A pelleted diet containing 30% protein was prepared using fish meal, meat and bone meal, mustard oilcake, rice bran, wheat bran and molasses, and was fed twice daily at a rate of 5% of fish biomass. Water quality parameters were measured fortnightly and the ranges of temperature, pH and dissolved oxygen were 27.5–1.3°C, 6.9–8.6 and 4.5–8.6 mg L^?1 respectively. Feed conversion ratios ranged from 2.05 to 2.20 among the treatments. Per cent survival (%) of prawns ranged from 72% to 78%, while it varied from 80% to 93%, 90% to 95% and 90% to 92% for catla, rohu and silver carp respectively. The results showed that there were no significant differences among the weight gains of prawn and carp in different treatments. However, the overall total production of prawn and fish together was significantly (P<0.05) higher in T₃ and T₄ compared with other treatments. The total production for 3 months ranged between 2618 and 2916 kg ha^?1. The production of prawn was significantly higher (361.3 kg ha^?1) in T₅ with a highest stocking density of 12 500 prawn ha^?1. Although there was no significant difference (P>0.05) between the total production of prawn and fish together in T₃ and T₄, the highest net profit (Tk. 69 006 ha^?1) was obtained in T₄. Therefore, from the result of the study it may be concluded that a stocking ratio of 4:1:2:1 of prawn:catla:rohu:silver carp at a total density of 20 000 ha^?1 may be recommended for prawn–carp polyculture in ponds.     

Carp edema virus in Polish aquaculture – evidence of significant sequence divergence and a new lineage in common carp Cyprinus carpio (L.)

Fish samples initially collected by local veterinarians on the common and koi carp farms in Poland between 2013 and 2015 as part of a KHV surveillance programme, when the water temperature was between 16 and 26 °C, and were also tested for CEV by qPCR. A partial 478 nucleotide fragment of the 4a gene was subsequently generated from 17 qPCR‐positive common carp Cyprinus carpio samples from 36 farm sites tested during the period. Sequence alignments and analysis revealed the presence of CEV in Poland both in common carp as well as in koi carp farms, and phylogenetic analysis assigned the Polish CEV sequences into three distinct genogroups. A lineage which includes the original sequences obtained from koi carp in Japan (genogroup II) included sequences from both koi carp and common carp, and the second lineage (genogroup I) contained sequences from common carp only. A third lineage (genogroup III) which was more closely related to the genogroup II also consisted of sequences from common carp only. The latter represents a lineage of CEV not previously described in the literature.     

Comparative study of acetylcholine synthesis in organs of freshwater teleosts

The activity of acetylcholine (ACh) synthesizing enzyme, choline acetyltransferase (ChAT), and the content of ACh were determined in the brain, heart, red trunk muscle and midgut of 12 freshwater teleost species belonging to eight families: carp (Cyprinus carpio), tench (Tinca tinca), silver carp (Hypophthalmichtys molitrix), bighead (Hypophthalmichtys nobilis), wels (Silurus glanis), cat fish (Ictalurus nebulosus), eel (Anguilla anguilla), rainbow trout (Oncorhynchus mykiss), pike (Esox lucius), pike-perch (Stizosteidon lucioperca), ruffe (Acerina cernua) and pumpkinseed (Lepomis gibbosus). The rate of ACh degradation in the same tissues was characterized by measuring the activity of acetylcholinesterase (AChE). Comparisons by statistical evaluation of cholinergic parameters in the corresponding organs were made between the species or families. The highest ACh concentration was found in the brain (between 9.6 and 16.0 nmol/g), and the gut (4.6 to 17.4 nmol/g), followed by the heart (1.4 to 3.9 nmol/g) and trunk muscle (1.2 to 3.8 nmol/g). Good correlations were found between the ACh content and the ChAT activity in all the organs studied. The correlation coefficients were 0.92 and 0.72 for the brain and heart, respectively. The activity of ChAT and the amount of ACh found in the brain and trunk muscle varied considerably from one family to another, but was of comparable degree within one family. It was concluded that differences in the cholinergic parameters may reflect different feeding and swimming behavioral patterns.     

Carbohydrate utilization by herbivorous and omnivorous freshwater fish species: a comparative study on gibel carp (Carassius auratus gibelio. var CAS III) and grass carp (Ctenopharyngodon idellus)

Two 8‐week feeding trials were conducted to evaluate dietary carbohydrate utilization by omnivorous gibel carp (Carassius auratus gibelio) (2.4 ± 0.1 g) and herbivorous grass carp (Ctenopharyngodon idellus) (6.5 ± 0.1 g). Five isonitrogenous (370 g kg^?1) and isolipid (70 g kg^?1) diets were formulated with increasing corn starch levels (60, 140, 220, 300 and 380 g kg^?1). Results showed that specific growth rate (SGR), feed efficiency (FE) and protein retention efficiency (PRE) of gibel carp significantly increased from dietary starch of 60 to 300 g kg^?1 and then decreased from 300 to 380 g kg^?1, but those of grass carp showed no significant differences between treatments. Independent of dietary starch levels, grass carp gained significantly higher FE and PRE than gibel carp. Feeding rate (FR) of gibel carp was significantly higher than that of grass carp. In two fish species, high dietary starch (300 and 380 g kg^?1) tended to obtain higher hepatosomatic index (HSI), serum triglyceride, hepatic lipid and body lipid contents. Serum glucose concentration of grass carp was not affected, while that of gibel carp fed the starch of 300 g kg^?1 diet was significantly lower than those of the fish fed other four diets (60, 140, 220 and 380 g kg^?1). Grass carp showed high tolerance to dietary starch while dietary corn starch should be no more than 300 g kg^?1 for gibel carp. High starch contents may cause lipid accumulation in the liver and body.     

Activity of digestive enzymes along the gut of juvenile red abalone, Haliotis rufescens, fed natural and balanced diets

Two carbohydrases (cellulase, lysozyme), three proteases (trypsin, aminopeptidase and non-specific protease), a non-specific lipase, and semiquantitative tests of 19 digestive enzymes were assayed in different gut sections of juvenile red abalone, Haliotis rufescens, in order to identify the regions where digestion takes place and investigate the extent to which diet composition can modify the digestive capacity of abalone. The abalone were fed either fresh kelp (K) or balanced diets containing 25 or 38% crude protein for 6 months. Enzyme assays were carried out on different sections of the abalone's gut at the end of this period. On a weight-specific basis, the digestive gland was the site containing most of the enzymes. On a protein-specific basis, two main digestion regions were identified: the digestive gland-stomach region that is characterized by high activities of cellulase and lysozyme, chymotrypsin and protease, and the mouth-intestine region with a typically high activity of lipase and amino peptidase. Significant dietary effects were observed on the activity of enzymes, especially in the digestive gland. Abalone fed with 25 and 38% crude protein diets exhibited higher cellulase (39.8 ± 4.6 and 14.2 ± 0.8 mU mg^− 1 protein, respectively) and lysozyme activities (88.0 ± 20.4 and 56.6 ± 15.7 U, respectively) than those fed with fresh kelp (5.5 ± 0.7 mU mg^− 1 protein and 17.1 ± 1.8 U). In contrast, higher protease activity was found in kelp-fed organisms (234.1 ± 20.4 μg product/mg protein) than those fed the 25 and 38% crude protein diets (109.5 ± 20.7 and 119.5 ± 20.5 μg product/mg protein, respectively). Semiquantitative API ZYM assays resulted in no clear food-specific effects on the activity of carbohydrases, proteases, ester hydrolases or phosphohydrolases, yet organ-specific differences were conspicuous in various cases, and generally agreed with quantitative results. It is suggested that the increased carbohydrase activity exhibited by organisms fed the balanced diets resulted from a combination of an increased number of resident bacteria in the abalone's gut and facilitated contact between dietary substrates and digestive cells. The present results indicate that H. rufescens can adjust their enzyme levels in order to maximize the acquisition of dietary protein and carbohydrates. This characteristic can be advantageously used to search for suitable diets in abalone aquaculture.     

Effects of common carp (Cyprinus carpio Linnaeus, 1758) and the African catfish (Clarias gariepinus Burchell, 1822) on growth and reproductive performance of native tilapia Oreochromis shiranus (Boulenger, 1896)

A study was conducted to assess the effects of common carp and the African catfish on growth and reproduction of the native tilapia Oreochromis shiranus in Malawi. The study was done from 1 May to 1 October 2018 at the National Aquaculture Centre (NAC), Zomba. Four triplicated treatments were used: O. shiranus + carp (T1), O. shiranus + catfish (T2), O. shiranus + carp + catfish polyculture (T3) and O. shiranus monoculture (T4). Fish were stocked at uniform density of 0.8 fish/m². Data collection was done once every month. Results showed that O. shiranus mean weight gain (%), specific growth rate (% body weight/day), average daily gain (g fish^?1 day^?1) and condition factor (g/cm³) were highest in T3 and lowest in T1 and T4 treatments. T3 had better water quality regime and higher tilapia biomass than T1 and T4 treatments. Tilapia fry production (no. fry pond^?1 day^?1) was highest in T4 but did not significantly differ (p > .05) between T2 and T3 treatments. It is concluded that the farming of common carp in aquatic ecosystems containing the African catfish may not adversely affect growth and reproduction of O. shiranus and that the polyculture of the African catfish, common carp and tilapia can be adopted to mitigate the potential adverse effects of carp on the environment and improve tilapia growth.     

Low-density silver carp Hypophthalmichthys molitrix (Valenciennes) polyculture does not prevent cyanobacterial off-flavours in channel catfish Ictalurus punctatus (Rafinesque)

Silver carp Hypophthalmichthys molitrix (Valenciennes) were co‐cultured with channel catfish Ictalurus punctatus (Rafinesque) in 0.4 ha earthen ponds to determine the impacts of carp grazing on pond phytoplankton communities and cyanobacterial off‐flavours in catfish. Carp were stocked at densities of 0, 75, or 250 fish ha^?1 in seven replicate ponds per treatment. The mean chlorophyll a concentrations (a measure of phytoplankton standing crop) steadily increased in all treatments from about 100 μg L^?1 in April to more than 400 μg L^?1 by mid‐October. Silver carp had no affect (P>0.1) on chlorophyll a concentrations across all sampling dates (April though October) or for sampling dates late in the growing season (August–October) when the prevalence of cyanobacterial off‐flavours among catfish populations is usually greatest. Silver carp did not eliminate odour‐producing cyanobacteria from pond phytoplankton communities: on sampling dates in September and October, three to six ponds in all treatments contained populations of the odour‐producing cyanobacteria Oscillatoria perornata, Anabaena spp., or both. Failure of silver carp to eliminate odour‐producing cyanobacteria resulted in a relatively high incidence in all treatments of ponds with off‐flavoured catfish. On sampling dates in September and October, catfish in three to five ponds in each treatment were tainted with either musty (2‐methylisoborneol) or earthy (geosmin) off‐flavours. The presence of silver carp had no obvious effect on off‐flavour intensity: on each sampling date, at least three ponds in each treatment contained catfish described as distinctly to extremely off‐flavored. Apparently, hypertrophic conditions in catfish ponds overwhelm the effect of silver carp grazing at the low carp densities used in this study.     

Introduction of jundia Rhamdia quelen (Quoy & Gaimard) and Nile tilapia Oreochromis niloticus (Linnaeus) increases the productivity of carp polyculture in southern Brazil

Fish polyculture is based on the assumption that each species has its own feeding niche and may increase the maximum standing crop of a pond by exploring a wider range of available food and ecological niches. In order to identify the better species ratio and to introduce jundia (JN) (Rhamdia quelen Quoy & Gaimard) and Nile tilapia (NT) (Oreochromis niloticus Linnaeus) in to the carp polyculture practiced in South Brazil, a 162‐day experiment was conducted, in 12 250‐m² earthen ponds (1.2 m deep). Treatment I (T‐I) contained 35% common carp, Cyprinus carpio (L.) (CC); 35% grass carp, Ctenopharyngodon idella Valenciennes (GC); 15% silver carp, Hypophthalmichthys molitrix Valenciennes (SC); and 15% bighead carp, Aristichthys nobilis Richardson (BC). Treatment II (T‐II) consisted of three ponds stocked at the following ratio: 17.5% CC, 35% GC, 15% SC, 15% BC and 17.5% JN. Treatment III (T‐III) consisted of three ponds with 35% CC, 35% GC, 7.5% SC, 7.5% BC and 15% NT. Treatment IV (T‐IV) consisted of three ponds with 17.5% CC, 35% GC, 7.5% SC, 7.5% BC%, 17.5% JN and 15% NT. No significant correlation was found between the treatments with different species ratio and water quality parameters. The final weight of different species, in different treatments, was statistically different. The major result was the clear positive effect on growth parameters observed by the introduction of JN and/or NT in to the carp polyculture. The yield per hectare was 2083.33±183 kg ha^?1 for polyculture with carp species; 2476.67±139.88 kg ha^?1 following the introduction of JN only; 2801.67±111.42 kg ha^?1 for isolated introduction of NT; and 2506.67±422.31 kg ha^?1 for simultaneous introduction of JN and NT. The introduction of JN and/or NT had a positive effect on growth parameters when compared with carp‐only polyculture. The reduction in CC ratio also had a positive effect on growth parameters.     

Results of comparative growing test of all-female and bisexual population in two-year-old common carp (Cyprinus carpio L.)

The aim of this study was to verify whetherall-female carp populations grow faster thanbisexual ones. All-female mirror and scalypopulations were obtained by crossingmasculinizated females (neomales) of Northernmirror carp (M72) with regular females of M72and scaly Ropsa carp (ROP) purebreds,respectively. All-female and bisexual progenyof both mirror and scaly carps were rearedseparately for one year. However, controlgroups of a distinct phenotype of scalinesswere put in ponds with tested fish to make anadjustment for fish weight, which could becaused by environmental influence. Nodifferences were found after eight weeks ofrearing between all-female and bisexualpopulations, but, all-female mirror carppopulation (M72) gained 29.7% more weight(P < 0.0001) by the end of the first year thanthe bisexual (68.5 g ± 15.8 against 52.8 g± 13.9; mean ± S.D., respectively).Before beginning the second growing season,each group was marked and stocked together intriplicate ponds. Corrected weight after secondgrowing season (P < 0.0062) was 9.9% higher inall-female mirror carps (395.9 g ± 98.6)compared to the bisexual (360.2 g ± 89.0).No significant differences were found incorrected weights between scaly all-female andbisexual crossbreds (522.4 g ± 102.4 and518.3 g ± 95.8, respectively). Nodifferences in survival of all-female andbisexual populations were observed.     

The influence of feeding rate on growth, feed efficiency and body composition of juvenile grass carp (Ctenopharyngodon idella)

An 8 weeks growth study was conducted to estimate the optimal feeding rate for juvenile grass carp (3.08±0.03 g, mean ± SD). Fish were fed with a casein purified diet (360 g protein, 56 g lipid and 3000 kcal total energy/kg dry diet) at six feeding rates: 1.0, 1.5, 2.0, 2.5, 3.0, 3.5% body weight per day (BW d⁻¹). Each feeding rate was randomly assigned to three tanks of fish with 30 fish per tank (50W × 50H × 100L, cm). Fish were maintained in recirculating systems at a water temperature of 24.97±2.23 °C and were fed four times per day. After 2 weeks, fish fed on 3.5% BW d⁻¹ could not finish the diet and this treatment was cut-off. Analysis of variance showed that growth performance was significantly (p<0.05) affected by different feeding rates. The nutrient compositions of whole body, muscle and liver were also significantly different among treatments. The body weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), apparent digestibility coefficiency (ADC), retention of protein (PR), mesenteric fat index, body moisture and protein content were significantly (p<0.05) affected by feeding rate. The WG, SGR and digestion rate were highest at 2% BW d⁻¹, although the FE and PER decreased with increasing feeding rate. Broken line analysis on specific growth rate indicated that the optimum feeding rate of juvenile grass carp is 1.97% body weight day⁻¹.     

Binding and bioactivity of insulin in primary cultures of carp (Cyprinus carpio) hepatocytes

Isolated carp hepatocytes cultured in serum-free, chemically defined medium were used to investigate within the same cell preparation characteristics of the binding of insulin as well as effects of insulin on cellular metabolism. The binding of human [¹²⁵I]-insulin to carp hepatocytes was studied in kinetic, saturation and displacement experiments. A dependency of insulin binding on the collagenase used for cell isolation was demonstrated. Insulin binding decreased during the first 12h of culture but remained constant during the following 12h. The kinetic experiments revealed that [¹²⁵I]-insulin binding reached a steady state within 20–30 min of incubation. The mathematical analysis of the saturation experiments demonstrated the existence of two populations of binding sites, one with high affinity (K_d1 = 5.5 pM) and low capacity (B_max1 = 0.14 fmol/mg protein or 77 binding sites/cell) and one with low affinity (K_d2 = 2.4 nM) and high capacity (B_max2 = 17.6 fmol/mg protein or 9623 binding sites/cell). In competition experiments, 312 pM [¹²⁵I]-insulin was displaced by cold insulin, IGF-I and IGF-II with IC₅₀ values of 2.2, 7.9 and 20.3 nM, respectively. Glucagon was without effect. Binding of insulin to carp hepatocytes resulted in a significant reduction of glucose release and a significant increase of protein synthesis as of de novo fatty acid synthesis. dedicated to Prof. Dr. W. Hanke on the occasion of his 65^th birthday.