Evaluation of poultry by‐product meal as partial replacement of fish meal in practical diets for juvenile tench (Tinca tinca L.)

The aim of this study was to evaluate different replacement levels of fish meal (FM) by poultry by‐product meal (PBM) on survival, growth performance and body composition of juvenile tench (Tinca tinca). A 90‐day experiment was conducted with 5 month‐old juveniles (31.95 mm total length, 0.396 g weight). Eight practical diets (50% crude protein) differing in the level of replacement of FM protein by PMB protein were tested: 0% (control), 25%, 31%, 37%, 43%, 49%, 55% and 61% corresponding to 0, 184.8, 229.2, 273.5, 317.8, 362.1, 406.5 or 450.8 g PBM kg^?1 diet respectively. Significant differences were not found (P > 0.05) between 25% replacement of FM protein by PBM protein (184.8 g kg^?1 PBM in diet) and control diet. At higher replacement levels, fish had significantly lower growth, higher feed conversion ratio and lower protein productive value (P < 0.05). Fish with externally visible deformities ranged from 1.1% to 3.3%. The relation among amino acid profiles of the diets, body composition, growth performance of juveniles and amino acid requirements of other fish species is discussed. Up to 184.8 g PBM kg^?1 diet can be included in diets for juvenile tench without impairing growth performance.     

Response of juvenile tench (Tinca tinca L.) fed practical diets with different protein contents and substitution levels of fish meal by soybean meal

A basal practical diet for juvenile tench (Tinca tinca) was formulated and elaborated to test several protein contents and substitution possibilities of fish meal (FM) by soybean meal (SBM) in a 90‐day trial with 5‐month‐old juveniles (30.54 mm TL, 0.30 g W). A factorial design included nine feeding treatments: three protein contents (50%, 40% or 30%) and three levels of replacement (0%, 25% or 45%) of FM protein by SBM protein. In addition, a commercial carp feed was used as reference. Final survival ranged from 98.2% to 99.4%. The 50% dietary protein with 0% or 25% replacement and 40% dietary protein with 25% replacement diets enabled higher growth (P < 0.05) and lower FCR (P < 0.05) than the rest of practical diets. Fish fed 50% dietary protein had similar growth than those fed carp feed (63.8% protein). Deformed fish averaged 1% for the practical diets and 87.6% for the carp feed. The basal practical diet has showed to be feasible and levels of 40–50% dietary protein with 25% replacement of FM protein by SBM protein can be recommended for juvenile tench aged 5–8 months.     

Fertilizing capacity and motility of tench Tinca tinca (L., 1758) sperm following cryopreservation

Experiments were carried out to develop an optimal cryopreservation protocol for tench sperm by testing the fertilizing capacity and motility parameters including progressive motility, curvilinear velocity (VCL) and linearity (LIN) of cryopreserved sperm. Three experiments were designed to this aim: first experiment where we tested the effects of two extenders (sugar‐based Grayling and ion‐based Kurokura 180) and two cryoprotectants (DMSO and methanol) on fertilization and hatching success; second where we tested the effect of cryoprotectant type (methanol or DMSO) in different concentrations (5%, 10% and 15%) on fertilization and hatching success; and third where we tested the effect of two cryoprotectants (methanol and DMSO) on sperm motility parameters (progressive motility, VCL and LIN) after 4 h post‐thaw storage (4°C). Sperm prepared with the sugar‐based Grayling extender displayed better fertilization and hatching rates independently of the applied cryoprotectant most likely due to glucose present which acted as an external cryoprotectant. Concerning cryoprotectant concentrations, the use of 10% methanol yielded the highest fertilization (85 ± 15%) and hatching (80 ± 13%) rates, which were significantly higher than in all other groups. During the post‐thaw storage time, 5% methanol, 10% methanol and 5% DMSO groups had significantly higher motility parameters than other groups and we observed no significant decline in any of the parameters during the storage time. Overall, we found that a sugar‐based extender in combination with methanol as cryoprotectant is suitable for the cryopreservation of tench sperm and allows storage of cryopreserved sperm for up to 4 h post thaw.     

Evaluation of pea proteins and poultry protein as fish meal alternatives in the diets for juvenile black sea bream,Acanthopagrus schlegelii

The potential of three different protein resources (pea protein isolate, PPI; pea protein concentrate, PPC; enzyme treated poultry protein, ETPP) as fish meal (FM) alternative protein in diets for juvenile black sea bream, Acanthopagrus schlegelii. (initial average weight 7.90 ± 0.13 g) was evaluated. Seven isonitrogenous and isoenergetic diets were formulated to replace FM at 0% (T0, control diet), 8% (designated as T1‐T3) and 16% (designated as T4‐T6) using PPI, PPC and ETPP respectively. Each diet was randomly assigned to triplicate groups of 25 juvenile fish for 8 weeks. At the end of the feeding period, survival rate was not significantly affected by dietary treatments. Growth performance in T6 (16% ETPP) group was significantly inferior to T0 group, however, weight gain and specific growth rate in other treatments showed no significant differences (P > 0.05). Mean feed intake, feed efficiency ratio and protein efficiency ratio were also poorer in fish fed in T6 than those of fish fed with the control diet respectively. Apparent digestibility coefficients (ADCs) of dry matter and crude protein for fish fed ETPP diets were significant lower than those of fish fed with the control diet, whereas ADCs of lipid were unaffected by dietary treatments. ADC's of dietary Leu, Ile, His and Lys was also significantly influenced. There were no marked variations in proximate compositions of dorsal muscle. With regard to plasma characteristics, significant difference was observed in triacylglycerol content. Ammonia concentration in plasma tended to increase in alternative protein diets as substitution level increased. There were significant differences in aspartate aminotransferase activities among groups, but alanine aminotransferase levels were unaffected by treatments. In conclusion, the present study demonstrated that PPI and PPC were potential protein sources for using in juvenile black sea bream diet. However, the substitution level of FM by ETPP should be limited within 16%.     

Effects of different diets on juvenile tench, Tinca tinca (L.) reared under controlled conditions

In a laboratory experiment at 28 °C, four commercial starters (Carp Starter, Uni Starter, Perla Plus, Asta) were fed intensively to 11-month-old juvenile tench Tinca tinca of initially 41 mm TL and 0.70 g BW, over a period of 120 days. Frozen chironomid larvae were fed to fish below satiation as a reference diet for comparison of the fish body chemical composition. Final survival rates of 99–100% and satisfactory growth were attained with all dry diets, ranging from 73.3 (Carp Starter) to 84.8 mm TL (Asta) and from 5.39 (Carp Starter) to 8.09 g BW (Perla Plus). External body deformities of up to 96.4% specimens appeared in those fed Uni Starter, Carp Starter and Perla Plus, whereas 0% were recorded for Asta and chironomids. Fish in groups with deformities showed significantly elevated lipid content in their bodies, lower ash content and higher condition coefficient values. Juveniles in groups without deformities did not substantially change lipid content, but the ash content increased. Thus, among four dry diets studied, only Asta starter can be fed effectively and safely to juvenile tench reared intensively under controlled conditions.     

Decapsulated Artemia cysts of different quality (high or low hatch‐rate) as direct food for tench (Tinca tinca L.) larvae

Three 30‐day experiments were conducted to evaluate decapsulated Artemia cysts with different quality (high or low hatch‐rate) as food for tench (Tinca tinca L.) larvae from the onset of exogenous feeding. In experiment 1, three diets were tested: Artemia nauplii‐only or cysts‐only for 30 days, and nauplii for the first 7 days and cysts thereafter. The cysts used had 86% hatching rate (high hatch‐rate cysts). The same feeding treatments were replicated in experiment 2 but with low hatch‐rate cysts (10% hatching rate). In experiment 3, five diets were tested: high hatch‐rate cysts only or low hatch‐rate cysts only for 30 days, and nauplii for the first 7, 4 or 2 days and low hatch‐rate cysts thereafter. In overall, survival was high, except with the low hatch‐rate cysts only diet. Feeding tench larvae with cysts resulted in higher growth and lower FCR compared to feeding with live nauplii only. High hatch‐rate Artemia cysts are a suitable food from the onset of exogenous feeding and low hatch‐rate cysts can be successfully used after 2–7 days feeding on nauplii.     

Diet and water temperature affect growth and body deformities in juvenile tench Tinca tinca (L.) reared under controlled conditions

The experiment was designed to determine the combined effect of fish diet and water temperature on juvenile tench Tinca tinca (L.). Three diets were used: commercial dry diet for fish Aller Futura (diet F); frozen Chironomidae larvae (diet C); and Aller Futura substituted with Chironomidae at a ratio of 3:2 (dry weight; diet FC). Daily food rations and duration of the experiment were adjusted to temperatures of 20°C, 23°C and 26°C based on a correction factor q equal to 1.000, 0.779 and 0.609 respectively. The experiment lasted 92, 72 and 56 days for the respective temperatures. No mortality occurred. The highest relative growth rates were found at 26°C in diets F and FC. The lowest food conversion ratio of 1.12–1.22 (recalculated for dry weight of feed diet) was determined in fish fed diet F at 23°C and 26°C. A high value of condition index appeared to be the early warning of decreasing biological quality of fish and deformities. The lowest incidence of fish with deformities (IDef) was found in groups fed diet C (<1%), while the highest (90%) in fish fed diet F at 26°C. A lower share of dry diet in the fish food and a lower water temperature led to a lower IDef. Thus, amount of dry feed in fish diet was the major factor inducing body deformities, while water temperature only modified the effects of the dietary factor. Diet C at 23–26°C was the most cost‐effective of the tested combinations of diet and temperature.     

Effects of fishmeal replacement by feather meal in practical diets for juvenile crayfish (Pacifastacus leniusculus Dana,Astacidae)

The aim of this study was to evaluate different replacement levels of fishmeal (FM) by feather meal (FeM) on survival and growth of juvenile crayfish (Pacifastacus leniusculus). An 80‐day experiment was conducted with stage 2 juveniles from the onset of exogenous feeding. Four practical diets (500 g kg^?1 protein) differing in the level of replacement of FM protein by FeM protein were prepared: 0% (control diet), 15% (8.2% dietary FeM), 25% (13.7% dietary FeM) or 35% (19.2% dietary FeM). Each diet was tested on grouped or individually isolated crayfish. Crayfish fed the control diet or 15% replacement achieved the highest survival (average of grouped and isolated: 88.2%) and growth (grouped and isolated: 13.58 mm carapace length, 523.2 mg weight) and the lowest feed conversion ratio (average of grouped and isolated: 1.11). Final growth of isolated crayfish was significantly higher than that of grouped crayfish for all diets. This study provides the first data on the substitution possibilities of FM by FeM in diets for freshwater crayfish. An 8.2% of FeM (15% replacement of FM protein) can be included in extruded diets for juvenile P. leniusculus during the first 80 days of intensive rearing without impairing growth or feed conversion.     

Combined effects of water temperature and daily food availability period on the growth and survival of tench (Tinca tinca) larvae

A 16‐day experiment was designed to find the best combination of water temperature (27, 30, 33°C) and daily duration of food availability (12, 18, 24 h) for larval tench (Tinca tinca) growth and survival. Larvae with an initial mean size of 5.7 mm total length (TL) and 0.7 mg wet body weight (BW) were stocked at 15 L^?1. Larvae were fed in excess with live Artemia nauplii with the period of food availability lasting 12, 18 or 24 h daily. The largest final larval size was recorded at 27 and 30°C in groups fed for 24 h a day (17.7 and 17.9 mm TL, 76.1 and 77.7 mg BW, respectively). The combination of the highest temperature and the longest daily food availability was the only set of conditions under which final larval survival was affected (95.4% survival; 98.7–99.9% under all other conditions). The combination of water temperature of about 28.6°C and continuous food availability is recommended as the optimum combination for rearing T. tinca larvae under controlled conditions. Providing continuous food supply to fish larvae under aquaculture conditions was also advantageous in helping to mitigate the effects of slower growth relative to developmental progress, which can occur at high water temperatures. However, should one wish to limit the daily feeding period to 12 h per day, the use of a water temperature between 27.4 and 27.9°C would be the best solution.     

Evaluation of a fish meal analogue as a replacement for fish meal in practical diets for Pacific white shrimp Litopenaeus vannamei

Three six‐week growth trials and a digestibility trial were conducted to evaluate a fish meal analogue (FMA) as a replacement for fish meal (FM) in shrimp feeds. Trials 1 and 2 evaluated and confirmed the potential of FMA supplementation (0, 48.5, 97, 145.5 and 194 g/kg) as a replacement for FM up to 200 g/kg without balancing for phosphorus (P) in practical diets for juvenile Pacific white shrimp L. vannamei. At the end of trial 1, shrimp offered diets containing 48.5 g/kg FMA exhibited significantly higher weight gain (WG) than those fed with the diet containing 145.5 g/kg FMA. At the end of trial 2, dietary FMA inclusion at 48.5 and 97 g/kg significantly improved WG and protein retention (PR), while reducing FCR and protein content of shrimp body compared to the diet containing 194 g/kg FMA. To determine whether P deficiency is the cause of reduced growth, the third trial was conducted utilizing equivalent diet but balanced for P. At the end of trial 3, shrimp fed diet containing 48.5 g/kg FMA+P showed significantly higher WG and PR than those fed diet containing 145.5 g/kg FMA+P. No decreasing trend of growth was detected in the diets containing FMA compared to the FM‐based diet. Apparent digestibility coefficients of dry matter, energy, protein and amino acids of FMA were determined using chromic oxide as an inert maker and the 70:30 replacement technique. The energy, protein and individual amino acid digestibility of FMA were significantly lower than those of soybean meal and FM which were run at the same time. Results of this work indicate that FMA can replace up to 200 g/kg FM in shrimp diets with supplemental inorganic P. Given the good growth across the range of inclusion without any indication of a growth depression, the low nutrient digestibility of FMA may be due to an atypical response or the product simply does not work with the testing technique.     

Soy protein concentrate as a substitute for fish meal in diets for juvenile Acanthopagrus schlegelii: effects on growth,phosphorus discharge and digestive enzyme activity

The current high demand and cost of fish meal (FM) necessities the evaluation of alternative plant protein ingredients in diets of farmed marine fish. A 56‐day feeding trial was performed to study the effects of replacement of FM with soy protein concentrate (SPC) in diets of Acanthopagrus schlegelii. Diets were prepared at levels of 0%, 30%, 47.5%, 65%, 82.5% and 100% SPC, respectively, replacing FM. The results indicated no significant differences (p > .05) in % weight gain (WG) and specific growth rate of fish fed S30% to S82.5% diets compared with the control diet while, further inclusion at 100% significantly depressed growth performance. SPC inclusion and phytase supplementation significantly affected the phosphorous discharge (P‐load) showing lowest value (3.83 ± 0.53 g/kg WG) in S100% compared to control (14.79 ± 0.37 g/kg WG) and in fish fed S30% diet (13.24 ± 0.89 g/kg WG) (p < .05). The results of this study showed that FM could be substituted up to 82.5% by SPC in the diet of Acanthopagrus schlegelii fingerlings (5.53 ± 0.12 g) without any adverse effects. Phytase supplementation SPC based diets could be effective in reducing the phosphorus load in the aquatic culture environment.     

Insemination, fertilization and gamete management in tench, Tinca tinca (L.)

Various procedures for artificial insemination in tench, Tinca tinca (L.) were re-examined with evaluation of fecundity of males and females among different tench strains. The objectives of this study were to enhance fertilization and hatching rates through optimization of the activation solution, the insemination process, the activation of gametes, and the elimination of eggs stickiness. Sperm for all experiments was collected directly into immobilization solution of modified Kurokura solution containing 180 mM of NaCl and stored at 2 °C for 2.5–5 h prior to the experiment. When dechlorinated tap water was used for activation a gamete ratio of 1150 spermatozoa per egg showed the best significant fertilisation and hatching rates. Optimal ratio between eggs (weight in g) and activation solution (in cm³) was 1:1. Different concentrations of activation solutions such as NaCl from 0 to 68 mM (0–136 mOsmol kg⁻¹) without buffer statistically decreased fertilization and hatching rates. The activation solution containing 17 mM of NaCl, 10 mM Tris–HCl, pH 8 and 9 significantly increased fertilization and hatching rates compared to dechlorinated tap water of pH 7 or activation solution containing 17 mM of NaCl, 10 mM Tris–HCl, pH 6 and 7. Adhesiveness of the eggs was successfully removed by incubation in Alcalase and activity: 3.16 Anson units per cm³.     

Effects of replacing fish meal with soya protein concentrate on growth,feed efficiency and digestibility in diets for snakehead,Channa striata

Soya bean meal‐based formulated feeds have recently become available for snakehead culture in Vietnam. This study was conducted to determine the appropriate replacement of fish meal (FM) protein by another soya product, soya protein concentrate (SPC), in snakehead (Channa striata) diets. Five iso‐nitrogenous (45% crude protein) and iso‐caloric (19 KJ g^?1) practical diets were formulated to replace 0% (control), 40%, 60%, 80% and 100% of protein FM by protein SPC (100% FM, 40% SPC, 60% SPC, 80% SPC and 100% SPC respectively). A digestibility experiment was also conducted with the same formulated diets with addition of 1% chromic oxide. Fish fed 100% FM and 40% SPC diets had significantly better growth and survival compared with other treatments. Feed intake, feed conversion ratio, protein efficiency ratio and net protein utilization, trypsin and chymotrypsin activities of experimental fish fed 100% FM and 40% SPC diets were significantly higher than those fed other diets. The apparent digestibility coefficient (ADC) of the diet and diet components, ADC_diet, ADC_protein and ADC_lipid, of fish fed diet 40% SPC and 100% FM treatment were significantly higher than those of other treatments. The cost/kg fish produced in diets 100% FM and 40% SPC was much lower compared with other treatments. Dietary inclusion levels of SPC in diet above 40% significantly affected fish survival, growth, digestibility and trypsin and chymotrypsin activities, although fish chemical composition was not greatly affected.     

Morphological changes of digestive structures in starved tench Tinca tinca (L.) juveniles

The aim of the study was to evaluate the effect of short-term starvation on the morphology of the digestive system of juvenile tench Tinca tinca (L.). The morphological changes in digestive structures of juveniles, fed 70 days starter or Chironomidae larvae, were examined after 1, 12, 24 and 48 h of starvation at 28 °C. The morphological changes in the organisation of the digestive structures were as follows: (1) Intestine – proteolysis of the intestinal mucosa, especially of enterocytes in apical part of mucosal folds; (2) Liver – progressive reduction of lipid vacuoles and glycogen granules, and, in effect, volume reduction of hepatocytes cytoplasm; (3) Pancreas – progressive degeneration of exocrine pancreatic cells, parallel with decrease of zymogen activity. The fish fed natural food prior to starvation seem to be more resistant to starvation than those fed starter.     

Evaluation of Calanus finmarchicus copepod meal in practical diets for juvenile Atlantic halibut (Hippoglossus hippoglossus)

The copepod, Calanus finmarchicus, has potential as a new ingredient in practical feeds for marine fish. Two experiments were conducted to evaluate the nutritional value of C. finmarchicus meals when fed to juvenile Atlantic halibut. The first study determined protein, lipid and energy digestibility coefficients of four C. finmarchicus meals prepared under different processing conditions. The second study evaluated growth and nutrient utilization efficiency of juveniles fed diets containing varying proportions of fish meal, plant meals and C. finmarchicus meal. Moisture, ash, protein, lipid and gross energy contents of the C. finmarchicus meals were 28–93, 74–138, 505–648, 123–269 g kg⁻¹, and 21–26 MJ kg⁻¹, respectively. Protein, lipid and energy digestibilities of C. finmarchicus meals were 91–99%, 90–95% and 90–99%. The digestibilities significantly decreased for the Calanus meals processed at higher temperatures. During the growth study, halibut fed a diet containing 240 g kg⁻¹ C. finmarchicus meal had significantly higher weight gain and growth rate than all other groups. Nitrogen and energy retention efficiencies ranged between 35–45% and 33–43%, and were significantly higher for fish fed 160–240 g kg⁻¹ C. finmarchicus meal than for fish fed plant protein and control diets. The results indicate that growth and nutrient utilization efficiency are improved in Atlantic halibut fed diets supplemented with C. finmarchicus meal.     

Induced meiotic gynogenesis in tench, Tinca tinca (L.) using irradiated heterogenic sperm

Effects of the starting time and duration of cold shock, as well as the source of heterogenic sperm on the percentage of viable gynogenic larvae (PVGL) in tench were studied. The DNA in sperm of red common carp (Cyprinus carpio var singuonensis) was inactivated by ultraviolet radiation prior to use to induce meiotic gynogenetic development in tench. In experiment 1, tench eggs were cold-shocked for 30 min starting at 1, 3, 5, 7, 10 and 15 min post activation. In experiment 2, cold shock began 5 min after activation and lasted for 10, 20, 30, 40, 50 min, respectively. Each experiment was run in triplicate using 3 tench females, and one group not treated with cold shock was included in each experiment to serve as a control group. In experiment 3, sperm of bigmouth buffalo (Ictiobus cyprinellus), red common carp or grass carp (Ctenopharyngodon idella) was used to induce gynogenesis in tench with a 20-min cold shock starting 5 min post activation. The results showed that PVGL from the control group was very low (0.11–0.47%). In experiment 1, the highest average PVGL (9.60%) was observed when cold shock treatment was applied 5 min post activation. When cold shock treatment was started 5 min post activation, duration of cold shock affected PVGL. Cold shock lasting 20 min resulted in the highest average PVGL (12. 57%) among the selected duration of cold shock studied in experiment 2. The average PVGL was 2.3, 8.6, and 9.3%, respectively, for eggs induced by sperm of bigmouth buffalo, red common carp and grass carp. Average PVGL was significantly lower for eggs induced by sperm of bigmouth buffalo, compared with that for eggs induced by sperm of the other two species. However, average PVGL were similar for eggs induced by sperm of red common carp and grass carp. In summary, the optimal conditions for gynogenesis in tench include the use of irradiated sperm of grass carp to activate the eggs and cold shock of 20 min starting 5 min post activation. Since female tench grow much faster to a larger size than male tench, gynogenesis of tench holds great potential for production enhancement.     

Egg oxidation status,antioxidant enzyme activities,lipid classes,fatty acid composition profile and embryo survival rates during in vitro oocyte ageing in tench Tinca tinca (Linnaeus, 1758)

The effect of in vitro storage of oocytes on embryos survival rate, egg oxidation status, antioxidant enzyme activities, lipid classes and fatty acid composition profile was investigated in common tench Tinca tinca. In order to identify the role of oxidative stress in the progress of oocyte ageing the levels of thiobarbituric acid reactive substances (TBARS) and carbonyls as indicators of lipid and protein oxidation were measured and the activity of antioxidant enzymes were examined. Stripped ova from six females were stored in cell culture plates at 20°C for up to 10 hr post‐stripping (HPS). The stored ova were fertilized and the embryo survival rates were assessed. The results indicated that tench eggs could be successfully stored in vitro for 4 hr after stripping at 20°C. Superoxide dismutase enzyme activity increased at 6 HPS, whereas glutathione peroxidase and glutathione reductase activities decreased in oocytes during in vitro storage (p < .05) at 4 and 8 HPSs, respectively. The level of malondialdehyde did not show any significant changes during the progress of oocyte ageing. Carbonyls increased up to 2 HPS and thereafter decreased significantly. However, ova ageing did not affect the main lipid class composition and the fatty acid composition of the eggs. Lower quality eggs exhibited lower levels of cholesterol but higher levels of triacylglycerol.     

Studies on sperm of diploid and triploid tench, Tinca tinca (L.)

The tench Tinca tinca is an interesting fish from the viewpoint of polyploidy and related atypical reproduction aspects. Triploid tench were produced artificially. Studies of spermiation as well as of sperm motility and structure were performed on several triploid and diploid males simultaneously with individual experimental crosses with diploid females to define their reproductive capacities. The testes of triploids visually looked less developed in the most of cases with lower sperm production (0.05 cm³ sperm per male), GSI and weight of testes compared to diploids (0.58 cm³ sperm per male). Analysis of variance showed significant influence of ploidy level on the percentage of motile spermatozoa. Triploidy did not change percentage of live spermatozoa and velocity of spermatozoa at the first time of sperm movement. The study of sperm structure by scanning electron microscopy revealed that most sperm cells were of normal structure with some anomalies. Sperm heads of triploid and diploid males were mostly round-shaped, 1.86±0.2 and 1.6±0.18 μm in diameter. The midpiece of triploid spermatozoa was slightly narrower than that of diploid ones with typical cylindrical shape. Flow cytometry revealed sperm cells of triploids to be largely aneuploid (1.47 n) with high mosaic DNA, oscillating from haploid DNA content (1.0 n) to diploid DNA content (1.9 n). Experimental crosses between triploid males and diploid females revealed that these males were capable to stimulate effective development with relatively high level of fertilization and hatching rates from 0 to 70%. In conclusion, triploidization does not seem to guarantee sterility of tench.     

Aurantiochytrium sp. meal can replace fish oil in practical diets for the juvenile Pacific white shrimp

This study evaluated the use of microalgae (Aurantiochytrium sp.) meal as a substitute for fish oil in the diet of juvenile Pacific white shrimp (Litopenaeus vannamei) reared in a clear‐water system. Dietary treatments at five replacement levels (0%, 25%, 50%, 75%, 100%) were performed in triplicate. After 46 days, only a slight difference in shrimp final weight was observed among treatments (0.61 g). An increase in final weight was observed with replacement of up to 50% fish oil for microalgae meal, while the optimal percentage of replacement estimated was 44.7%. Feed conversion rate (FCR) of animals fed a diet of Aurantiochytrium sp.meal to replace up to 50% fish oil decreased, and the optimal percentage of replacement estimated was 49.3%. The fatty acids profile in shrimp muscle tissue demonstrated an increase in docosahexaenoic acid (DHA) from 10.03% to 14.28% with increased replacement of fish oil by microalgae meal in the diet. Therefore, the partial replacement of fish oil by microalgae meal resulted in improved shrimp growth and FCR, and total replacement of dietary fish oil had no negative effects on these parameters. In addition, inclusion of microalgae meal raises the level of DHA in shrimp muscle.     

Production, release and olfactory detection of sex steroids by the tench (Tinca tinca L.)

The present study is concerned with pheromone communication in tench (Tinca tinca L.), establishing firstly whether males have a high olfactory sensitivity to some typical teleost sex steroids and prostaglandins; and secondly whether males and females might be able to synthesise and release some of these steroids into the water. The C₂₁ steroid, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was found to give large electro-olfactogram responses with an estimated threshold of detection of 10⁻¹² M. The male tench were equally sensitive to glucuronidated 17,20β-P (10^−11.6 M) but 100 times less sensitive to sulphated 17,20β-P (11^−9.7 M). Preliminary data from cross-adaptation studies suggest that both the free and conjugated forms are detected by the same olfactory receptor(s). Male tench also had high olfactory sensitivity to prostaglandin F_2α (PGF_2α) and 15-keto PGF_2α (11^−11.5 and 10^−11.4 M). They were relatively insensitive, however, to testosterone (T), androstenedione (AD), 11-ketotestosterone (11-KT), 17β-oestradiol (E₂), 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) and 17,20α-dihydroxy-4-pregnen-3-one (17,20α-P). Radioimmunoassays were used to measure the steroids in plasma and water and all samples were processed for the measurement of free, sulphated and glucuronidated fractions. In females, free 17,20β-P, 17,20α-P, free and glucuronidated T, and AD in plasma showed the largest increases in response to injection with mammalian gonadotropin-releasing hormone analogue (GnRHa) or Ovaprim (a mixture of GnRHa and a dopamine inhibitor). Free 17,20β-P was released into the water at the greatest rate. Plasma concentrations of the two conjugated forms of 17,20β-P were also elevated 18 h after the administration of GnRHa, but not by as much as the free steroid. In males, AD and 11-KT showed the greatest increase in response to GnRHa and were moreover released into the water at a higher rate in the treated group than in the control. The data support a possible pheromonal role for free and glucuronidated 17,20β-P. This revised version was published online in July 2006 with corrections to the Cover Date.