Effect of electrical stunning at slaughter on the quality of farmed turbot (Psetta maxima)

Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.     

Effects of dietary astaxanthin concentration and feeding period on the skin pigmentation of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

A single‐factor experiment was conducted to investigate the effects of dietary astaxanthin concentration on the skin colour of snapper. Snapper (mean weight=129 g) were held in white cages and fed one of seven dietary levels of unesterified astaxanthin (0, 13, 26, 39, 52, 65 or 78 mg astaxanthin kg^?1) for 63 days. Treatments comprised four replicate cages, each containing five fish. The skin colour of all fish was quantified using the CIE L^*, a^*, b^* colour scale after 21, 42 and 63 days. In addition, total carotenoid concentrations of the skin of two fish cage^?1 were determined after 63 days. Supplementing diets with astaxanthin strongly affected redness (a^*) and yellowness (b^*) values of the skin at all sampling times. After 21 days, the a^* values increased linearly as the dietary astaxanthin concentration was increased before a plateau was attained between 39 and 78 mg kg^?1. The b^* values similarly increased above basal levels in all astaxanthin diets. By 42 days, a^* and b^* values increased in magnitude while a plateau remained between 39 and 78 mg kg^?1. After 63 days, there were no further increases in measured colour values, suggesting that maximum pigmentation was imparted in the skin of snapper fed diets >39 mg kg^?1 after 42 days. Similarly, there were no differences in total carotenoid concentrations of the skin of snapper fed diets >39 mg kg^?1 after 63 days. The plateaus that occurred in a^* and b^* values, while still increasing in magnitude between 21 and 42 days, indicate that the rate of astaxanthin deposition in snapper is limited and astaxanthin in diets containing >39 mg astaxanthin kg^?1 is not efficiently utilized. Astaxanthin retention after 63 days was greatest from the 13 mg kg^?1 diet; however, skin pigmentation was not adequate. An astaxanthin concentration of 39 mg kg^?1 provided the second greatest retention in the skin while obtaining maximum pigmentation. To efficiently maximize skin pigmentation, snapper growers should commence feeding diets containing a minimum of 39 mg unesterified astaxanthin kg^?1 at least 42 days before sale.     

收获沙棘振动器试验研究

该项研究的核心是研制振动器,通过振动果枝的方式来收获沙棘果实。2003到2004年间,基于我们的试验研究结果显示,沙棘品种＂印度夏季＂通过用频率为40Hz,振幅为15mm,10s为一振动周期的果枝振动器可有效获得果实。利用这个参数的振动可以有效获得90%的果实,且对果枝的损害很小,从果枝上下来的叶片、芽及木枝的碎片也很少。在2003年进行了最原始的研究,2004年测试发现这种方法存在一定缺陷。发电机利用机轴进行来回的旋转运动,利用这个原理进行各种振幅试验,但这对果树各部分会产生大量的压力。用1.5kW的电机可以在车间及没有农业机械的土地上进行试验,但这个过程需要人工看护。最原始的方法效率不高且过程复杂。2005年进行了设备的改进,通过凸轮产生的振动来驱动液压马达。尽管这种方法使用时间还很短,但是它的振动功能还是非常显著的。如果选在最佳采摘季节收获果实,收获的果实品质最佳,同时对果树的伤害也是最小的。如果在每个季节采摘500株或是更少果树的果实,这种振动收获果实的方法是一种最佳选择。     

QTL for IHNV resistance and growth identified in a rainbow (Oncorhynchus mykiss) × Yellowstone cutthroat (Oncorhynchus clarki bouvieri) trout cross

Infectious hematopoietic necrosis virus (IHNV) is a major constraint to rainbow trout culture. Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) have greater resistance to this virus than do rainbow trout (O. mykiss), but the genetic mechanism of this resistance is not understood. We conducted a genome scan using a backcross of cutthroat trout into a rainbow trout background to estimate the number and locations of quantitative trait loci (QTL) associated with IHNV resistance and growth in trout. IHNV resistance was considered in terms of both survival (binary trait) and days to death (quantitative trait). The genetic map was scanned using interval mapping via two different approaches: one model considered survival alone and a second two-part model combined both survival and days to death. Three QTL were significantly (P ≤ 0.05) associated with virus resistance genome-wide, explaining 32.5% of the phenotypic variation. Cutthroat alleles at two of these QTL resulted in increased resistance to the pathogen, as expected. No growth QTL were detected in this cross. We suggest that these traits are genetically independent.     

A review of cyanobacterial odorous and bioactive metabolites: Impacts and management alternatives in aquaculture

Increased demand has pushed extensive aquaculture towards intensively operated production systems, commonly resulting in eutrophic conditions and cyanobacterial blooms. This review summarizes those cyanobacterial secondary metabolites that can cause undesirable tastes and odors (odorous metabolites) or are biochemically active (bioactive metabolites) in marine and freshwater, extensive and intensive aquaculture systems. For the scope of this paper, biochemically active metabolites include (1) toxins that can cause mortality in aquaculture organisms or have the potential to harm consumers via accumulation in the product (hepatotoxins, cytotoxins, neurotoxins, dermatoxins, and brine shrimp/molluskal toxins), (2) metabolites that may degrade the nutritional status of aquaculture species (inhibitors of proteases and grazer deterrents) or (3) metabolites that have the potential to negatively affect the general health of aquaculture species or aquaculture laborers (dermatoxins, irritant toxins, hepatotoxins, cytotoxins). Suggestions are made as to future management practices in intensive and extensive aquaculture and the potential exposure pathways to aquaculture species and human consumers are identified.     

Differences in swimbladder volume between Baltic and Norwegian spring-spawning herring: Consequences for mean target strength

Fish swimbladders, where present, contribute most to the scattering of sound by fish, as measured by the target strength (TS). The volumes of the swimbladders of two different European stocks of Atlantic herring were compared to consider the effect on estimates of TS. Swimbladder volumes of Baltic and Norwegian spring-spawning herring (Clupea harengus) were measured, together with individual herring fat content. Swimbladder volumes were found to differ significantly between the two herring stocks. Baltic herring have a larger swimbladder volume, which is suggested to be associated with the fish's low fat content, which in turn may be linked to its specific energy budget and the low salinity of the Baltic Sea. A buoyancy model that considered the different salinity conditions and fat proportions was used to evaluate the observed differences in swimbladder volume. The swimbladder volume data were subsequently used to model the mean target strength as a function of depth and growth pattern. Backscattering of the swimbladder was modelled using the modal-series-based deformed-cylinder model (MSB-DCM), describing the swimbladder as a gas-filled, elongated prolate spheroid. The fish body component was modelled as a fluid-filled ellipsoid using the distorted wave Born approximation (DWBA). Modelling results support a different TS-to-size relationship for Baltic herring, with a stronger echo, due to the larger swimbladder. Depth- and length-dependent TS relationships based on the model results are suggested.     

The role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem

We evaluated the role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem using the Ecopath/Ecosim approach. As basic input data for the Ecopath/Ecosim model, we used estimates of biomass from bottom trawl surveys and age-structured population models, production/biomass (P/B) ratio, consumption/biomass (Q/B) ratio, diet composition (DC), and fisheries harvests for each component of species or species groups. We estimated the trophic level of each component, niche overlaps among flatfishes, and the impacts of competition and predation on flatfish species in the eastern Bering Sea ecosystem. Based on those estimates, we developed the tropho-dynamic structure of the ecosystem, and the model was used to simulate ecological effects of fishery exploitation patterns. No single flatfish species appeared to have a profound and uniquely important role in the organization and structure of the ecosystem. Instead, the most important component among the guild of flatfish species appeared to be yellowfin sole Pleuronectes asper, which had greater biomass than other flatfish and a relatively diverse diet among the small flatfish species. Pacific halibut Hippoglossus stenolepis, Greenland turbot Reinhardtius hippoglossoides, and arrowtooth flounder Atheresthes stomias were important keystone predators in the eastern Bering Sea ecosystem together with some groups of marine mammals and sea birds. Intra flatfish complex cannibalism was not observed, however, substantial diet overlaps were common in the flatfish guild system.     

Angling for endangered fish: conservation problem or conservation action?

Recreational angling has been implicated in population declines of some marine and freshwater fish, but this activity is rarely considered as a threat or even halted when endangered species are targeted. Indeed, in some cases, anglers are drawn to fish for rare or endangered species. Conservation‐oriented behaviours such as catch‐and‐release are often practiced voluntarily due to the ethics of anglers, yet even in these cases, some fishing mortality occurs. Nonetheless, there are many indirect conservation benefits associated with recreational angling. Here, we present a series of case‐studies and consider whether catch‐and‐release angling for endangered fish is a conservation problem or a conservation action. If recreational angling activities contribute to population‐level consequences that are contrary to recovery strategies, then angling for endangered species would seem to be a poor option. However, as revealed by several case‐studies, there is much evidence that anglers are vocal and effective proponents of fish and habitat conservation, and for endangered species, they are often the only voice when other stakeholders are not engaged. Anglers may contribute directly to conservation actions via user fees (e.g. licences), philanthropic donations or by volunteering in research, education and restoration activities. However, it is important to quantify post‐release mortality as well as understand the full suite of factors influencing a given population or species to know the potential risks. A risk assessment approach outlined in the paper may be used by managers to determine when the benefits of angling for endangered species outweigh the risks.     

Design and development of a geothermal temperature control system for broodstock management of channel catfish Ictalurus punctatus

A control system was designed to raise and maintain water temperatures within 0.03-ha earthen ponds to a range conducive for spawning (24–30 °C) channel catfish Ictalurus punctatus. Heating was done during February 2001 to April 2001, when temperatures would have otherwise prohibited spawning (<24 °C). Temperature was increased from 10 °C (ambient) by 2 °C per day, and maintained at 27 °C, by the addition of geothermally warmed water (36 °C). The control system substantially increased the controllability and precision of heating ponds compared to manual operation. Systems were designed to control sets of four ponds. In designing this control system, consideration of biological constraints was essential. Reproduction in channel catfish is most strongly influenced by temperature. Because cold fronts are common during the winter and early spring (January–March), it was essential to ensure that pond temperatures did not fall below the range for spawning. Constraints on the heating rate and temperature variability to maintain fish health and stimulate spawning behavior were considered. Components of the control system included temperature measurement devices (type-T thermocouples), a central electronic control unit, electronic switches and electrically actuated ball valves. In response to the temperature sensed by each thermocouple, the controller sent a message to close or open the valve. When the valve was opened, warm water was added to the pond to increase the average pond temperature. Hardware and algorithm design and initial system testing were the major components of this project. The final design incorporated information on relevant biological parameters and safety features including peak pond temperature, independent aeration and water pressure control mechanisms. Initial results indicate successful control of this biological system, and ongoing studies suggest similar mechanisms may be used for additional control objectives. In particular, this system could be used to vary pond temperatures to study biological responses and to cool ponds by addition of well water during summer months.     

Fertilizer ammonium : nitrate ratios determine phosphorus uptake by young maize plants

We investigated the interacting effects of inorganic nitrogen and the main inorganic phosphorus form in dairy manure (dicalcium phosphate, CaHPO₄) on growth, nutrient uptake, and rhizosphere pH of young maize plants. In a pot experiment, three levels of CaHPO₄ (0, 167, and 500 mg P pot^?1) were combined with nitrogen (637 mg N pot^?1) applied at five NH₄‐N : NO₃‐N ratios (0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0) and a nitrification inhibitor in a concentrated layer of a typical acid sandy soil from Denmark. ¹⁵N‐labeled NH₄‐N was applied to differentiate the role of nitrification and to partition nitrogen uptake derived from NH₄‐N. Among treatments including nitrogen, shoot biomass, rooting and phosphorus uptake were significantly higher at the five‐leaf stage when CaHPO₄ was applied with NH₄‐N : NO₃‐N ratios of 50 : 50 and 75 : 25. In these treatments, rhizosphere pH dropped significantly in direct proportion with NH₄‐N uptake. The fertilizers in the concentrated layer had a root‐inhibiting effect in treatments without phosphorus supply and in treatments with pure NO₃‐N or NH₄‐N supply. Increased nitrogen uptake as NH₄‐N instead of NO₃‐N reduced rhizosphere pH and enhanced acquisition of applied CaHPO₄ by young maize plants, which may have positive implications for the enhanced utilization of manure phosphorus.