Impact of heat stress,nutritional restriction and combined stresses (heat and nutritional) on growth and reproductive performance of Malpura rams under semi‐arid tropical environment

A study was conducted to assess the combined effect of heat stress and nutritional restriction on growth and reproductive performances in Malpura rams. Twenty‐eight adult Malpura rams (average body weight (BW) 66.0 kg) were used in this study. The rams were divided into four groups: CON (n = 7; control), HES (n = 7; heat stress), NUS (n = 7; nutritional stress) and COS (n = 7; combined stress). The study was conducted for a period of 2 months. CON and HES rams had ad libitum access to their feed while NUS and COS rams were under restricted feed (30% intake of CON rams) to induce nutritional stress. The HES and COS rams were kept in climatic chamber at 42 °C and 55% relative humidity for 6 h a day between 10 : 00 h and 16 : 00 h to induce heat stress. Body weight increased significantly (p < 0.05) in CON as compared to NUS and COS. When compared within groups, scrotal width morning, scrotal width afternoon, scrotal circumference morning and scrotal circumference afternoon were significantly (p < 0.05) larger in CON while smaller in COS rams. The higher testicular length was recorded both during morning (p < 0.05) and afternoon (p < 0.01) in COS rams while the lowest in NUS rams. The highest plasma testosterone concentration was recorded in CON and lowest in COS rams. Semen volume and mass motility also differed significantly (p < 0.05) between the groups. The highest semen volume and mass motility was recorded in CON and NUS while lowest in both HES and COS rams. It can be concluded from this study that when two stressors occur simultaneously, they may have severe impact on reproductive performance of rams.     

The post-ovulatory rise in progesterone is lower and the persistence of oestrous behaviour longer during the first compared with the second cycle of the breeding season in mares

Mares are seasonally polyoestrous breeders. Therefore, the first ovulation of the season, following winter anoestrus, is the only cycle in which mares ovulate without the presence of an old CL from the previous cycle. The objective of this study was to compare the length of oestrous behaviour, and plasma progesterone concentrations during the early post-ovulatory period between mares after the first and second ovulation of the breeding season. Overall, 38 mares and 167 oestrous periods were used in the study. From those, 11 mares were used during the first and subsequent oestrous period to measure and compare the post-ovulatory rise in progesterone concentration, whereas all the mares were used to compare the length of the post-ovulatory oestrous behaviour between the first and subsequent cycles of the breeding season. The persistence of the post-ovulatory oestrus was longer (p < .001) following the first ovulation of the year (median of 52 h) compared with the subsequent ovulations (median of 36 h for second and later ovulations groups; n = 38 mares). The progesterone concentration at any of the four 8 h-intervals analysed (28, 36, 76 and 84 h post-ovulation) was lower (p < .01) following the first versus the second ovulation of the year. By 36 h post-ovulation the progesterone concentration of mares at the second ovulation of the year had passed the threshold of 2 ng/ml (2.1 ± 0.33 ng/ml), whereas in the first cycle it was 1.2 ± 0.13 ng/ml. In conclusion, mares had lower progesterone concentrations in their peripheral circulation and longer persistence of oestrous behaviour following the first ovulation of the year compared with the second and subsequent ovulatory periods of the breeding season.     

Performance,milk fatty acid composition and behaviour of high-yielding Holstein dairy cows given a limited grazing period

The effects of a limited grazing period on the performance, behaviour and milk composition of high-yielding dairy cows were examined. A total of 56 Holstein cows yielding 44.7 ± 0.42 kg/day were allocated to one of four treatments in one of two, 4-week periods. Treatments were as follows: control (C)—cows housed and offered TMR ad libitum; early grazing (EG)—cows grazed for 6 hr after morning milking then housed; delayed grazing (DG)—cows returned to housing for 1 hr after morning milking followed by grazing for 6 hr, then housed; restricted TMR (RT)—cows grazed for 6 hr after morning milking, then housed and fed TMR at 75% of ad libitum. Intake of TMR was highest in cows receiving C, intermediate in EG and DG, and lowest in RT at 26.9, 23.6, 24.7 and 20.3 kg DM/day respectively. Pasture intake was similar in cows receiving EG or DG, but was higher in RT at 2.4, 2.0 and 3.5 kg DM/day respectively. Milk yield was similar between cows receiving C, EG or DG, but lowest in RT at 45.7, 44.2, 44.9 and 41.7 kg/cow, respectively, while milk fat content of C18:3 n-3 was increased by grazing. Cows in C spent more than 55 min/day longer lying and had three additional lying bouts/day, while lying bouts were shorter than for cows receiving EG, RT or DG. It is concluded that high-yielding cows can be grazed for 6 hr/day with little impact on performance, provided TMR is available ad libitum when housed.     

消费者生鲜水果线上购买迁徙行为及其影响因素

为探索消费者生鲜水果线上购买迁徙行为的影响因素和机制路径,本研究基于PPM理论,构建结构方程模型分析了消费者生鲜水果线上购买迁徙行为及其影响因素,并运用多群组分析不同消费者行为影响因素的差异性。结果表明：1）价格、信息、服务不满意构成正向影响消费者生鲜水果线上购买迁徙行为的推力因素;感知有用性、搜索、消费体验感构成正向影响迁徙行为的拉力因素;程序转移成本构成负向影响迁徙行为的锚定因素。2）锚定因素负向调节推力因素对迁徙行为的作用效果。3）性别、年龄、学历水平三个人口统计特征在不同假设路径中的影响较为显著。其中女性、30岁及以下、学历水平大专以上的群体更愿意在线上渠道购买生鲜水果。结论丰富了生鲜水果领域消费者迁徙行为的研究成果,并为生鲜电商可持续发展提供了启示。     

Bigeye tuna (Thunnus obesus) vertical movements in the Azores Islands determined with pop-up satellite archival tags

Movement patterns of 17 bigeye tuna (Thunnus obesus) near the Azores Islands were analyzed between April and May 2001 and 2002 using pop‐up satellite archival tags. Despite short attachment durations (1 to 21 days, 8.2 days on average), their vertical movements revealed much shallower distribution of bigeye tuna in comparison with previous studies in the tropical Pacific and tropical Atlantic. Depth and temperature histograms were unimodal, although overall depth distribution during the day was deeper than during the night due to daily incursions in deeper waters. Although generalized additive models showed significant non‐linear relationships with weight of the fish and sea level anomaly (as a proxy for variability of thermocline depth), the effect of these variables on bigeye depth appeared minor, suggesting that vertical movements of bigeye in the Azores during the spring migration may be influenced by food availability in upper water layers.     

The understudied and underappreciated role of predation in the mortality of fish released from fishing gears

The assumption that animals released from fishing gears survive has frequently been scrutinized by researchers in recent years. Mortality estimates from these research efforts can be incorporated into management models to ensure the sustainability of fisheries and the conservation of threatened species. Post‐release mortality estimates are typically made by holding the catch in a tank, pen or cage for short‐term monitoring (e.g. 48 h). These estimates may be inaccurate in some cases because they fail to integrate the challenges of the wild environment. Most obvious among these challenges is predator evasion. Stress and injury from a capture experience can temporarily impair physiological capacity and alter behaviour in released animals, a period during which predation risk is likely elevated. In large‐scale commercial fisheries, predators have adapted their behaviour to capitalize on impaired fishes being discarded, while in recreational catch‐and‐release fisheries, exercise and air exposure can similarly impede the capacity for released fish to evade opportunistic predators. Owing to the indirect and often cryptic nature of this source of mortality, very few studies have attempted to document it. A survey of the literature demonstrated that <2% of the papers in the combined realms of bycatch and catch‐and‐release have directly addressed or considered post‐release predation. Future research should combine field telemetry and laboratory studies using both natural and simulated predation encounters and incorporate physiological and behavioural endpoints. Quite simply, predation is an understudied and underappreciated contributor to the mortality of animals released from fishing gears.     

Diet composition of sturgeon fry (Acipenser persicus) reared in fertilized earthen ponds

Artificial rearing of fry has been introduced as an alternative to supply fry and juvenile sturgeon in order to restock the depleted sturgeon population in the Caspian Sea. The aim of this study is to assess the feed selection characteristics of sturgeon (Acipenser persicus) fry during the period in which they stay in earthen ponds before being released into the river. Sturgeon fry weighing around 150 mg were introduced into five almost similar‐sized earthen ponds. The ponds were enriched with fertilizer to supply natural food for the fries. A weekly sample of six specimens was collected from each pond during the 5 weeks of the experiment. All collected fish were weighed and then dissected for inspection of the stomach and the intestine content. The overall stomach content measured from 150 fish showed that around 74% of the stomach content was composed of chironomids and the rest was daphnia and cyclops. At the beginning of the study (first 2 weeks), sturgeon fry feed more on daphnia and cyclops; this trend, however, reversed in the last 2 weeks of the study. In conclusion, sturgeon fry feed on three prey groups—chironomids, daphnia and cyclops—during their lifespan in earthen pond. Feeding on chironomids larvae increased with sturgeon fry size.     

Feeding responses of juvenile shrimp Litopenaeus vannamei (Boone) fed at different frequencies under laboratory conditions

In shrimp farms, food partitioning during the course of the day is contradictory, ethology studies may help in determining the proper frequency. Litopenaeus vannamei juveniles were placed in 30 L aquariums (41 m⁻²), exposed to a 12:12 h light–dark cycle. Feeding was provided at 10% of biomass three, four and seven times per day, with observations made in 15 min h⁻¹ windows, initiated after the ration was offered. Latency to access the feeding tray and to start eating was recorded using instantaneous focal sampling and digestive tract filling (DTF) by the continuous focal method. Weight gain was recorded at the end of the experiment. We performed seven repetitions, with 28 individuals observed for 33 days for each treatment (490 h of observation). The three-times offering induced less latency for accessing the tray and for ingesting the feed as well as a higher DTF when compared with the other frequencies. Animals fed three and four times had similar weight gains, and were greater than those fed seven times. Our results indicate that a more spaced food offering stimulates the search for and ingestion of feed. As compared with other frequencies, the three-times-per-day option assumes lower labour costs and a more efficient use of the feed.     

Evaluation of codends with sorting grids, exit windows, and diamond meshes: Size selection and fish behaviour

This paper presents the results of an experiment aimed at improving the size selection of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Nordic bottom trawl fishery. Three systems simulating commercial conditions were tested: a 135 mm diamond-mesh codend fitted with a 55 mm sorting grid (Sort-V); a 135 mm diamond-mesh codend fitted with two lateral exit windows; and a codend built entirely of 155 mm diamond mesh. The selectivity curves showed similar selection ranges (SR) for the three systems. For cod, the mean SRs were around 8 cm, while for haddock, they were around 6 cm. All the estimated l₅₀ values were far above the minimum landing sizes (MLS). For cod, the mean l₅₀s were 56.1, 53.9, and 60.7 cm for the sorting grid, exit windows, and diamond-mesh configurations, respectively, while for haddock, they were 50.2, 50.6, and 49.9 cm, respectively. Underwater observations revealed that most of the fish escaped from the grid and exit-window codends as soon as they reached the vicinity of the sorting device. In contrast, fish remained inside the diamond-mesh codend for a longer time, and consequently were more exposed to physical damage before escape. In addition, many fish escaped from this codend during haul back and these fish were not likely to survive due to the rapid changes in pressure. Thus, the selectivity results obtained with this type of codend should be interpreted carefully.