The effect of fish size and stocking density on the weaning success of pond-cultured pikeperch Sander lucioperca L. juveniles

The effect of initial fish size (small with TL = 40.3 ± 2.3 mm and W = 0.42 ± 0.15 g, medium with TL = 56.2 ± 2.7 mm and W = 1.66 ± 0.4 g, and big with TL = 71.0 ± 3.2 mm and W = 2.95 ± 0.65 g) and stocking density of identical fish with TL = 40.3 ± 2.3 mm and W = 0.42 ± 0.15 g (1; 2; 4; 8 fish l^?1) on weaning success was evaluated in pond-cultured pikeperch. The trial was divided into weaning (12 days) and post-weaning (16 days) periods. Small juveniles reached significantly higher specific growth rate (SGR = 1.6 ± 0.2 % day^?1) and survival rate (S = 81.7 ± 2.7 %) and lower cannibalism (C = 3.0 ± 0.75 %) compared to medium and large juveniles (SGR = 0.3–0.5 % day^?1, S = 65.3–76.5 %, C = 6.5–7.5 %) during the weaning period. The higher survival rate was found at the two higher densities (S = 72.0–79.1 %) during the weaning period. The lowest survival rate (S = 38.9 ± 2.7) was observed at the lowest fish density. Fish stocking density did not affect growth, condition, or cannibalism rate during the weaning period. Similar trends of growth, survival, and cannibalism of weaned juveniles were observed during the post-weaning period. A mass weaning trial verified experimental results showing small pikeperch juveniles to reach satisfactory growth rate (SGR = 1.4 ± 0.1 and 7.2 ± 0.2 % day^?1), survival (S = 78.7 ± 3.0 % and 97.6 ± 1.0 %), and cannibalism (C = 4.0 ± 1.5 % and 2.5 ± 1.0 %) rates during the weaning and post-weaning periods. No body or fin deformities of weaned juveniles were observed.     

Combined effect of weaning time and co‐feeding duration on growth and survival of peled Coregonus peled (Gmelin) larvae

The study investigated the combined effect of weaning from live feed to a commercial dry pellet at 10, 15, 20, 25 or 30 days posthatching (dph) and co‐feeding for 1, 3 or 6 days on survival and growth of Coregonus peled larvae. Additional groups fed only live Artemia sp. nauplii (ART), and only Biomar LARVIVA ProWean 100 (DRY) were included. A final survival rate of 66.4%–85.5% was observed in groups weaned after 20 dph. Final body weight (BW) and total length (TL) were significantly lower in groups weaned at 10 and 15 dph, regardless of the duration of co‐feeding. Larvae reached 29–37 mg BW and TL of 17.7–19.0 mm in groups weaned at 20, 25 and 30 dph. The recommended minimum duration of feeding with live food, based on these results, is 20 days. Based on the significantly higher yield of larvae weaned after 20 dph irrespective of co‐feeding duration, it can be concluded that abrupt weaning to dry food after 20 days of feeding with live prey can provide adequate production while reducing the effort and costs associated with live feed.     

Hormonal induction of ovulation in pikeperch (Sander lucioperca L.) using human chorionic gonadotropin (hCG) and mammalian GnRH analogue

The aim of the present study was to study spawning stimulation in artificial reproduction of females pikeperch (Sander lucioperca L.) using “Chorulon” containing the human chorionic gonadotropin (hCG) and compare with “Supergestran” containing a mammalian GnRH ([D-Ala⁶]GnRHProNhet) analogue. The females were divided into eleven experimental groups and injected with hCG at 250, 500, 750, and 1 000 IU kg^?1 body weight (BW) and mGnRHa at 1, 2.5, 5, 10, 25, and 50 μg kg^?1 BW. In all treatments, a single intramuscular injection of hormone was performed. Control group was injected with 0.9 % NaCl, 0.9 cm³ kg^?1 BW. The average percentages of ovulating females were 88.5 ± 12.3 and 80.8 ± 10.9 % in hCG- and mGnRHa-treated groups, respectively. The average diameter of eggs was 0.95 ± 0.06 and 0.98 ± 0.06 mm in hCG- and mGnRHa-treated groups, respectively. Neither ovulation rate nor diameter of egg was statistically differed among hormonally treated groups. Statistical difference was observed only in hatching rate, where the average were 73.6 ± 14.4 and 50.6 ± 17.7 % in hCG and mGnRHa-treated groups, respectively. Among hormonally treated groups, the best results were observed in groups treated with hCG at 500 and 750 IU kg^?1 and in groups treated with mGnRHa at 25 μg kg^?1. No ovulation was observed in the control group. This study indicated successful ovulation in pikeperch using a single intramuscular injection of hCG or mGnRHa analogue.     

Effects of metabolic inhibitors on activity of Cry1Ab toxin to inhibit growth of Ephestia kuehniella larvae

BACKGROUND: Although the toxins of Bacillus thuringiensis Berliner (Bt) are frequently used to control lepidopteran pests, the tolerance or resistance of some lepidopteran moth strains may limit Bt applications. In this study, insecticidal cocktails consisting of sublethal doses of Cry1Ab toxin and additive compounds were tested for their suppressive effect on larval relative growth rate (RGR) in Ephestia kuehniella Zeller under laboratory conditions.RESULTS: In the first step, the suppressive effect of diflubenzuron, soybean trypsin inhibitor (STI) and chitinase on RGR was confirmed. In the second step, these compounds were incorporated into a mixture of crushed kernels of Bt maize hybrid MON 810-YieldGard((R)) and its isoline with concentrations of Cry1Ab toxin ranging from 0.011 to 0.091 microg g(-1) diet. An additive effect on the suppression of larval RGR in E. kuehniella was found in a combination of diflubenzuron, STI and STI + chitinase as secondary compounds in insecticidal cocktails. Chitinase showed no additive effect on RGR.CONCLUSION: The highest suppression level was found in cocktails with STI + chitinase as a secondary compound. It is hypothesized that the protease inhibitor (STI) protects both chitinase and Cry1Ab proteins from endogenous proteases in the larval midgut and prolongs their insecticidal activities. The possible application of insecticidal cocktails in the control of E. kuehniella is discussed. Copyright (c) 2008 Society of Chemical Industry.     

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.     

Fin damage and growth parameters relative to stocking density and feeding method in intensively cultured European perch (Perca fluviatilis L.)

We evaluated the relationship of stocking density to survival, growth performance and fin condition of European perch Perca fluviatilis with hand feeding and self-feeders. Hand-fed perch (body weight 19.1 ± 5.1 g and total length 107 ± 9 mm) were reared at 0.5, 1.0, 1.5 and 2.0 fish/L. Self-feeding perch (body weight 25.4 ± 3.9 g and total length 128 ± 7 mm) were reared at stocking densities of 0.6, 1.0 and 1.4 fish/L. Pond-reared perch served as a comparison group for fin damage assessment. We found no differences in survival rate among stocking densities with either feeding method. Hand-fed fish displayed the highest weight gain and SGR at stocking density of 0.5 fish/L. The self-feeding fish showed a non-linear association of weight gain with stocking density with the highest growth at 1.0 fish/L. Fin length was noticeably greater in pond-reared fish compared with RAS-reared fish regardless of feeding method. In both experiments, fin length relative to standard length showed a negative relationship with stocking density, with pectoral fins showing the greatest effect. Fin condition deteriorated with increasing stocking density, and growth was highest at 0.5 and 1.0 fish/L in hand-fed and self-feeding fish, respectively.     

Arthropod pests and their natural enemies in stored crops in northern Namibia

A survey of stored product pests, their natural enemies, grain storage and pest management approaches in northern Namibia was conducted. The survey revealed five types of crop commodities (pearl millet, sorghum, cowpea, maize, feed mixture) stored in four types of grain stores (baskets, bag stags-flat stores, concrete bin, metal containers). No synthetic pesticides or plastic sheeting was recorded. Wooden-ash natural pesticide is the only protectant used. Ten insect pest species were found affiliated to the orders of Coleoptera (Attagenus fasciatus, Callosobruchus subinnotatus, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica and Tribolium castaneum), Lepidoptera (Corcyra cephalonica, Sitotroga cerealella), Psocoptera (Liposcelis paeta) and Blattodea (Blattella germanica). Out of these, seven species were recognized as new stored-products pests for Namibia. Although listed for southern Africa region, no storage pest-mites (Acari) and Sitophilus spp., Prostephanus sp. or Trogoderma sp. beetles were traced. We found four new species of natural enemies of storage pests recruiting from insects (Habrobracon hebetor, Cephalonomia wattersoni, Brachymeria sp.) and mites (Blattisocius tarsalis). The occurrence of natural enemies indicates a potential for pest bio-control in Namibian grain stores.     

Inversion relationship between action threshold and economic/aesthetic injury?level?for the control of urban and quarantine pests

Traditional agricultural pest control IPM theory claims that the action threshold (AT) is lower than the economic (EIL) or aesthetic injury level (AIL). Urban and quarantine pests are tolerated at the zero or near-zero population level. In the cases where responsive pest control strategies are used instead of preventive ones, inherently AT should be non-zero and higher than EIL/AIL. The constraints of the implementation of preventive treatment (= zero AT) for some urban pest problems requiring the zero EIL/AIL are discussed.     

Inversion relationship between action threshold and economic/aesthetic injury level for the control of urban and quarantine pests

Traditional agricultural pest control IPM theory claims that the action threshold (AT) is lower than the economic (EIL) or aesthetic injury level (AIL). Urban and quarantine pests are tolerated at the zero or near-zero population level. In the cases where responsive pest control strategies are used instead of preventive ones, inherently AT should be non-zero and higher than EIL/AIL. The constraints of the implementation of preventive treatment (= zero AT) for some urban pest problems requiring the zero EIL/AIL are discussed.