Improved survival and growth performances with photoperiod and feeding schedule manipulation in bagrid catfish Mystus nemurus (Cuvier & Valenciennes 1840) larvae

Manipulation of photoperiod: 24 h light (24L), 12 h light:12 h dark (12L:12D) and 24 h dark (24D); and feeding schedules: day and night feeding (DNF), day feeding (DF) and night feeding (NF) was conducted to determine effects on survival, cannibalism and growth of larval bagrid catfish Mystus nemurus 2–14 days after hatching (dAH). Photoperiod insignificantly affected all parameters. Feeding schedule significantly affected survival and total length at 6 (P < 0.049; P < 0.009), 10 (P < 0.033; P < 0.000) and 14 dAH (P < 0.013; P < 0.000), respectively, but affected cannibalism at 10 (P < 0.043) and 14 dAH (P < 0.013). Survival for DNF was significantly higher than DF. Cannibalism for DNF was significantly lower than NF at 10 and 14 dAH. Total length for DNF was significantly higher than DF and NF at 10 and 14 dAH. At 14 dAH, feeding schedule significantly affected feed intake, final weight and coefficient of variation. For feed intake and final weight, DNF was significantly higher than DF and NF. For coefficient of variation, NF was significantly higher than DF. This study suggests that larval bagrid catfish can be reared at 24L, 12L:12D or 24D but should be fed day and night for improved growth, survival and reduced cannibalism.     

Effects of feeding conditions and size differences on aggressive behaviour and cannibalism in the Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel) larvae

We examined the effects of feeding conditions and size differences on the aggressive behaviour and cannibalism in Pacific bluefin tuna (PBT) Thunnus orientalis larvae. In a 24 h experiment, restricted feeding alone was found to remarkably increase the frequency of aggressive behaviour, which was further elevated by differences in fish size. In a 4‐day rearing experiment, while aggressive behaviour was increased by restricted feeding alone, the frequency of cannibalism did not change significantly. Although the frequency of aggressive behaviour did not increase with difference in size factor, small fish in this group gradually tended to die over 4‐day period. In the restricted feeding and size difference group, large fish were observed to bite the small fish, and almost all the small fish died on the day after the start of the experiment. These results suggest that the aggressive behaviour of PBT larvae is chiefly increased by the shortage of live food; however, deaths related to cannibalism mainly occurred in small larvae and rapidly increased with food restriction and differences in fish size.     

驯食强度对鳡幼鱼驯食效果及生长的影响

研究了驯食强度对鳡（Elopichthys bambusa）驯食成功率(WSR)、残食率(CR)、死亡率(MR)及生长的影响。实验分6组,于1.0×1.0×1.0 m³网箱中进行,每日驯食2次,驯食强度分别为每次驯食1.0 h（S1组）、1.5 h（S2组）、2.0 h（S3组）、2.5 h（S4组）、3.0 h（S5组）和4.0 h（S6组）。结果显示：WSR随着驯食强度的增强显著升高后降低(P<0.05);总CR随着驯食强度的增加而显著降低(P<0.05);总MR随着驯食强度的增加先降低后略有升高。实验终期,体重特定生长率(SGR_BW),全长特定生长率(SGR_TL)和肥满度(CF)随驯食强度的增强显著增大(P<0.05);体重变异系数(CV_BW)随驯食强度增加显著减小(P<0.05)。综上所述,在实验条件下,鳡最佳驯食强度为每次驯食3 h。     

Larval cannibalism rates in the mangrove crab Ucides cordatus (Decapoda: Ocypodidae) under laboratory conditions

Predation of zoeas by megalopae of Ucides cordatus is frequently observed in the laboratory during larval rearing, a phenomenon that could considerably reduce the output of larviculture. Experiments were carried out in the present study to assess how the survivorship of larvae at the end of the larviculture is influenced by cannibalism by megalopae on the larvae of earlier stages, as well as on other megalopae. In addition, tests were performed to assess whether the adoption of different feeding protocols can decrease cannibalism rates. Experiments were carried out in plastic vials containing ocean water (salinity 25 g L^?1) under controlled environmental conditions (26 °C and 16:8 h LD photoperiod). An ensemble analysis of all the developmental stages indicated that zoeal mortality rates were significantly higher in the presence of megalopae, a result that is consistent with cannibalism by megalopae. However, separate analysis for each developmental stage indicated that only zoea IV, V and VI show reduced survivorship. No cannibalism was detected among megalopae. Food supplementation using Artemia sp. at a density of 6 nauplii mL^?1 proved to be successful in reducing cannibalism rates, whereas supplementation at a lower density (0.3 nauplii mL^?1) failed to show such an effect. The implications of these results for the larviculture of U. cordatus are discussed.     

规格差异和饵料密度对杂交鳢(Channa maculate♀×C.argus♂)仔稚鱼残食的影响

采用试验生态学的方法,研究了残食行为、规格差异和饵料密度对杂交鳢仔稚鱼残食的影响.结果表明:当杂交鳢仔鱼全长达到1.30 cm(7日龄)时出现残食.同规格杂交鳢仔稚鱼饱食状况下几乎没有残食现象,而全长2.21cm仔鱼在饥饿状况下表现出了较高的残食率;规格差异越大,残食率越高,全长比为0.57:1.00、0.50:1.00、0.39:1.00的3个试验组的残食率分别为18.35%、46.65%、61.67%,差异显著;饵料缺乏时的残食率显著高于饵料充足时,全长2.21 cm杂交鳢仔鱼饲养7 d,不投饵和饱食情况下的残食率分别为46.67%和1.11%,差异显著;以日投喂率0%、5%、15%饲养杂交鳢仔稚鱼(全长比为0.50:1.00)5 d,残食率依次为83.33%、35.00%、3.33%,差异显著.可见,规格差异和摄食状况对杂交鳢仔稚鱼的残食都有显著影响.生产上,小个体和大个体全长比低于0.60;1.00时,及时分池饲养是提高杂交鳢仔稚鱼成活率的重要途径.     

Self-grading of larval pike-perch (Sander lucioperca), triggered by positive phototaxis

The phototactic behavior of pike-perch (Sander lucioperca) larvae from 1 to 50 days post hatch (dph) was evaluated using a channel system with 0 and 700 lx light treatment. The findings of this work show larval pike-perch to be highly positive phototactic during its larval stage with a peak of positive phototactic behavior between 10 and 22 dph. After 22 dph positive phototaxis decreased and pike-perch increasingly preferred the lower light treatment. In a second experiment observed positive phototaxis was used to evaluate the effectiveness of a light triggered self-grading mechanism for pike-perch larvae at 16, 22, 28 and 34 dph. The use of larvae’s positive phototaxis for a gentle self-grading was successful at 16 and 22 dph and decreased the length variability between 14 and 18% at 16 dph and between 18 and 28% at 22 dph. Whereas the grading at 28 and 34 dph led to an insufficient reduction in length heterogeneity. As a result the light triggered self-grading has the potential to be implemented in future rearing protocols and to be applied on pike-perch between 16 to 22 dph. Furthermore, it is suggested to consider a light triggered self-grading mechanism within upcoming tank designs for the rearing of larval pike-perch.     

A Molecular Approach for Detecting Stage-Specific Predation on Lygus hesperus (Hemiptera: Miridae)

A molecular gut analysis technique is described to identify predators of Lygus hesperus (Knight), a significant pest of many crops. The technique is unique because it can pinpoint which life stage of the pest was consumed. Sentinel egg masses designed to mimic the endophytic egg-laying behavior of L. hesperus were marked with rabbit serum, while third instar and adult L. hesperus were marked with chicken and rat sera, respectively. Then, the variously labeled L. hesperus life stages were introduced into field cages that enclosed the native arthropod population inhabiting an individual cotton plant. After a 6-h exposure period, the predator assemblage, including the introduced and native L. hesperus population, in each cage were counted and had their gut contents examined for the presence of the variously marked L. hesperus life stages by a suite of serum-specific enzyme-linked immunosorbent assays (ELISA). The whole-plant sampling scheme revealed that Geocoris punticpes (Say) and Geocoris pallens Stal (Hemiptera: Geocoridae) and members of the spider complex were the numerically dominant predator taxa in the cotton field. The gut content analyses also showed that these two taxa appeared to be the most prolific predators of the L. hesperus nymph stage. Other key findings include that Collops vittatus (Say) (Coleoptera: Melyridae) and Solenopsis xyloni McCook (Hymenoptera: Formicidae) appear to be adept at finding and feeding on the cryptic L. hesperus egg stage, and that L. hesperus, albeit at low frequencies, engaged in cannibalism. The methods described here could be adapted for studying life stage-specific feeding preferences for a wide variety of arthropod taxa.     

An experimental comparison of cannibalistic response in different Arctic charr (Salvelinus alpinus (L.)) stocks

Abstract– The cannibalistic response of four domesticated Arctic charr stocks were compared experimentally using a radiographic technique. Charr from Arctic Spitsbergen (80°N) consistently exhibited a much higher frequency of cannibalistic response than fish from three charr strains from mainland Norway (70°N). The results indicate that the extent of cannibalistic feeding in Arctic charr is population specific and support the hypothesis that charr from Arctic populations have stronger cannibalistic tendencies than do fish from more temperate regions.     

内外因素对凡纳滨对虾仔虾同类相残的影响

为了解凡纳滨对虾(Litopenaeus vanname)仔虾同类相残行为,分析了个体规格、幼体密度、饵料丰度、充气4个内、外因素对其同类相残的影响。结果表明,幼体密度、饵料丰度、个体规格显著影响凡纳滨对虾的同类相残率。当幼体密度从50 ind/L提高到120 ind/L时,平均日相残率升高190%;当幼体密度大于120 ind/L时,平均日相残率增加幅度相对较小。饵料密度20 ind/m L组与不投喂组相比,平均日相残率降低78.5%。不同个体规格仔虾混养时,对虾的平均日残率显著高于单养组。高充气量组,相残率下降。可见,饵料缺乏可能是导致仔虾同类相残的主要原因,高放养密度和个体规格差异等因素会诱发和促进同类相残的发生。     

Production and predation rates in a cannibalistic Arctic char (Salvelinus alpinus L.) population

Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha⁻¹. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha⁻¹. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha⁻¹ · year⁻¹, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha⁻¹ · year⁻¹. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.