Does overfeeding affect tench Tinca tinca (L.) juveniles?

Duplicate groups of tench (Tinca tinca) juveniles (mean weight 0.69 g) were fed at 28 °C for 70 days either a commercial formulated diet, Futura, or frozen Chironomidae larvae at four levels: below satiation, at about satiation, above satiation and well above satiation. These are represented by the feeding groups F1–F4 and C1–C4, respectively. No mortality was observed throughout the experiment. In groups F2–F4 a considerable incidence of uneaten food (>40% observations), deformities of the caudal penduncle, retarded growth, elevated condition coefficient (>1.2), reduced amounts of minerals in the tissue (<10% dry matter), high C/N ratio (>5) and high caloric value of the tissue (>28 J mg⁻¹ dry matter) (the latter two suggesting excessive fat deposits), were found. The combination of these indices was indicative of overfeeding in fish fed the Futura diet at the daily doses ≥2.7% fish biomass. First symptoms of overfeeding: a considerable incidence of uneaten food, retarded growth, and elevated C/N ratio were observed in the group fed Chironomidae larvae at the highest level, (C4, wet Chironomidae 20.7% of the fish biomass daily, that is, 3.9% of dry chironomids per fish biomass and day). Thus, restricted daily doses of formulated diet not exceeding 2.5% fish biomass are recommended for tench juveniles aged 130–200 days post hatch. Safe daily doses of frozen Chironomidae (in terms of larvae dry weight) remain below 3.5% of fish biomass.     

Effects of sub-lethal CO2(aq) concentrations on the performance of intensively reared gilthead seabream (Sparus aurata) in brackish water: Flow-through experiments and full-scale RAS results

The effects of sub-lethal CO_2(aq) concentrations were tested for the first time on gilthead seabream (Sparus aurata) juveniles (4–25 g; 64 growth days) and adult (∼300–400 g; 71 d) fish, both in fully controlled pilot tests and the latter also as part of full-scale RAS (recirculating aquaculture system) operation. In the pilot experiments (concentration range 5.2–56.3 mg CO₂/L) the specific growth rate, mortality rate, and physical fish disorders were monitored. In the full scale experiment, two groups of fish, originally from the same batch, were exposed for 197 d to controlled (by NaOH dosage) and uncontrolled pH conditions, resulting in exposure of the fish to significantly different CO_2(aq) concentrations. The pilot results showed, as expected, that the seabream fish grew faster at the lower CO₂ concentrations and that the growth rate of both juveniles and adult fish was only minimally inhibited up to roughly 20 mg CO₂/L (compared to a previously published curve). Mortality rate was considerable only at the highest CO₂ concentration (∼56 mg CO₂/L). Physical irregularities were not observed, apart from abnormally high absence of swim bladder at the highest CO_2(aq) treatment. The (statistically significant) results from the full-scale RAS operation showed that growing gilthead seabream for 197 d at roughly constant and relatively low (∼16 mg/L) CO_2(aq) concentration resulted in fish with ∼10% larger mean weight relative to the fish grown in ponds in which CO_2(aq) was not controlled and its concentration fluctuated daily between 19 and 37 mg/L.     

组合材料的变形控制

组合材料的变形控制杨敏琴，申冬建（河北农业大学城建学院，保定０７１００１）关键词组合材料：弯曲变形ＤｅｆｏｒｍａｔｉｏｎＣｏｎｔｒｏｌｏｆＣｏｍｐｏｓｉｔｅＭａｔｅｒｉａｌｓ￥ＹａｎｇＭｉｎｑｉｎ；ＳｈｅｎＤｏｎｇｊｉａｎ（ＡｇｒｉｃｕｌｔｕｒａｌＵ...