Ices on the surface of triton

The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton.     

Effects of soil bulk density and strength on seedling growth of annual ryegrass and tall fescue in controlled environment

Grasses sown with minimal tillage commonly exhibit slower establishment and lower herbage yield than those sown into a conventionally tilled seedbed. Some of the difference in performance may be attributed to differences in bulk density between tilled and untilled ground. It is not known if performance rankings of grass cultivars established in clean‐tilled ground remain valid in more compacted soil characteristic of no‐till seeding. Seedlings of five cultivars of Italian ryegrass (Lolium multiflorum Lam.) [IRG] and five cultivars of tall fescue [Festuca arundinacea Schreb. also known as Lolium arundinaceum Schreb. (Darbysh.)] [TF] were grown in pots of Coyle or Stephenville series soils (sandy loam and loamy sand respectively) packed to 0·75, 0·88 or 1·00 of maximum packing densities, established as 1·47 and 1·68 g cm^?3 for Coyle and Stephenville soil respectively. Leaf appearance was measured until seedling harvest at 540 growing degree days after emergence. Increased bulk density decreased leaf appearance rates, reduced final leaf and tiller numbers and aerial and root biomass at harvest in both IRG and TF. Among cultivars within species, there was no difference (P > 0·05) in response to measured parameters to change in bulk density. Seedling growth and development of IRG were consistently greater than that of TF but showed greater reduction in response to increased soil bulk density. Soil strength provided a better indicator of likely seedling response to soil compaction than bulk density. The results suggest that cultivar rankings obtained under conventional tillage are likely to be valid with no‐till planting.     

Hypoxia affects performance traits and body composition of juvenile hybrid striped bass (Morone chrysops × M. saxatilis)

Performance traits and body composition of juvenile hybrid striped bass (Morone chrysops × M. saxatilis) in response to hypoxia were evaluated in replicate tanks maintained at constant dissolved oxygen concentrations that averaged 23.0 ± 2.3%, 39.7 ± 3.0% and 105.5 ± 9.5% dissolved oxygen saturation. Fish were fed a commercially formulated feed daily to apparent satiation. Total feed intake and fish growth and yield increased linearly in response to increased dissolved oxygen concentration. Nutrient utilization was reduced significantly only at the greatest level of hypoxia. With the exception of whole body protein content, whole body compositional indices and nutrient retention efficiencies were linearly related to dissolved oxygen concentration. Results demonstrate that as hypoxia becomes more severe, juvenile hybrid striped bass feed intake is reduced, which affects growth and nutrient retention.     

Consumer preferences for farmed tilapia in Tanzania: A choice experiment analysis

ABSTRACT

This study used a choice experiment to analyze the preferences of consumers for the attributes of tilapia (price, mode of production, product form, and size), a major aquaculture product in Tanzania. The results showed that consumers were willing to pay a price 665.020 Tanzanian shillings (TZS) lower for farmed tilapia than for wild tilapia; a price TZS 833.210 and TZS 1799.110 higher for medium-size and large-size tilapia respectively than for small-size tilapia; and a price TZS 1214.090 higher for fresh tilapia than for smoked tilapia. Consumers’ willingness to pay less for farmed tilapia than for wild tilapia is mainly attributed to issues related to taste and availability. It was also found that consumers were heterogeneous in their preferences for all the tilapia attributes (mode of production, size, and form) considered in this study.     

Renal myxosporidiasis in Asian horned frogs (Megophrys nasuta).

Renal myxosporidiasis and associated lesions were seen in Asian horned frogs, Megaphrys nasuta, at the Detroit Zoological Institute and the Toledo Zoo. The organism was identified as Chloromyxum sp. on the basis of histopathology, cytology, and electron microscopy. Histologic changes in the kidneys included varying degrees of renal tubular dilation and necrosis, and mild to severe nonsuppurative tubulointerstitial nephritis associated with vegetative stages of the myxosporidian. This is the second known identification of Chloromyxum sp. in amphibian kidneys, and the first report of death attributed primarily to the parasite.     

Effect of soybean meal diets on the growth performance,ammonia excretion rates,gut histology and feed cost of Nile tilapia (Oreochromis niloticus) fry

Aquaculture development in Ghana is currently limited by inadequate supply of fingerlings and prohibitive cost of commercial feeds among other challenges. This study tested the feasibility of using low‐cost feeds containing soybean meal instead of fishmeal for nursing Nile tilapia (Oreochromis niloticus) fry. Three isonitrogenous (~48% crude protein) and isoenergetic (~17 kJ/g) diets with increasing inclusions of soybean meal as partial replacements for fishmeal were formulated. A commercial fishmeal‐based fry feed served as the control diet. Triplicate groups of 225 fish per tank (average initial weight: 2.09 ± 0.14 g) were stocked in a recirculating aquaculture system and fed the experimental diets for 21 days. Afterwards, we investigated the postprandial metabolism, nutrient digestibility, growth and gut histology in Nile tilapia fry. Simple economic analyses were also conducted to assess the cost‐effectiveness of the diets used in the feed trial. The dietary inclusions of the soybean meal significantly reduced feed cost by ~43% relative to the control diet. The growth performance and feed utilization parameters did not vary significantly among the different treatments. The soybean diets elicited significant reductions in villi heights and goblet cell numbers, which corresponded with increasing dietary levels of soybean meal. This study confirms the potential of soybean meal as a partial replacement for fishmeal in Nile tilapia fry diets in terms of lower feed costs, fish growth performance, nutrient digestibility and postprandial nitrogenous excretions. The inclusion of soybean, however, affected negatively the gut integrity of the fry.     

Stocking strategies for production of Litopenaeus vannamei (Boone) in amended freshwater in inland ponds

The performance of the Pacific white shrimp Litopenaeus vannamei (Boone) under various stocking strategies was evaluated in earthen ponds filled with freshwater amended with major ions. Six 0.1‐ha earthen ponds located in Pine Bluff, AR, USA, were filled with freshwater in 2003 and 2004, and potassium magnesium sulphate added to provide 50 mg K⁺ L^?1 and stock salt added to provide 0.5 g L^?1 salinity. In 2003, three ponds either were stocked with PL₁₅ shrimp (39 PL m^?2) for 125 days of grow out or with PL₂₅ shrimp for 55 days (23 PL m^?2) followed by a 65‐day (28 PL m^?2) grow‐out period. In 2004, ponds were stocked with 7, 13 or 30 PL₁₅ m^?2 for 134 days of grow out. Salinity averaged 0.7 g L^?1 during both years, and concentration of SO₄^?2, K⁺, Ca²⁺ and Mg²⁺ was higher, and Na⁺ and Cl^? was lower in amended pond water than in seawater at 0.7 g L^?1 salinity. Potassium concentration in amended water was 52–61% of the target concentration. Shrimp yields ranged from 3449 kg ha^?1 in 2003 to 4966 kg ha^?1 in 2004 in ponds stocked with 30–39 PL₁₅ m^?2 for a 125–134‐day culture period. At harvest, mean individual weight ranged from 17.1 to 19.3 g shrimp^?1. In ponds stocked with PL₂₅ shrimp, yields averaged 988 and 2462 kg ha^?1 for the 1st and 2nd grow‐out periods respectively. Gross shrimp yield in 2004 increased linearly from 1379–4966 kg ha^?1 with increased stocking rate. These experiments demonstrated that L. vannamei can be grown successfully in freshwater supplemented with major ions to a final salinity of 0.7 g L^?1.     

Development of phytoplankton communities and common off-flavors in a biofloc technology system used for the culture of channel catfish (Ictalurus punctatus)

The use of biofloc technology production systems continues to increase in the aquaculture industry worldwide. Recent research demonstrated that outdoor biofloc systems can be used to produce high yields of channel catfish (Ictalurus punctatus). However, studies have not yet been performed to determine the development and composition of phytoplankton communities and related off-flavor problems in these biofloc production systems. In this study, water samples were collected biweekly from May to November and channel catfish samples were collected during harvest in November from nine 18.6 m² biofloc culture tanks. Water and fillet samples were analyzed for levels of the common off-flavor compounds geosmin and 2-methylisoborneol (MIB). The development and composition of phytoplankton communities in each culture tank was also monitored. In addition, water and biofloc samples were evaluated to assess the microbial sources of geosmin and MIB within the culture tanks. Phytoplankton (including algae and cyanobacteria attached to bioflocs) biomass, as determined by concentrations of chlorophyll a in the water, gradually increased in all tanks over time. Phytoplankton communities that developed in the culture tanks were dominated by fast-growing, unicellular and small colonial types of green algae (chlorophytes) and diatoms (bacillariophytes) and slower growing, small colonial types of cyanobacteria (cyanophytes). A positive correlation (p < 0.05) between cumulative feed addition and chlorophyll a concentration was found. Although geosmin and MIB were present in the culture water of each tank during most of the study, levels were typically low and only one tank yielded catfish with geosmin and MIB in their flesh at levels high enough to be designated as off-flavor. A positive correlation (p < 0.05) between cumulative feed addition and MIB concentrations in the water of culture tanks indicates a greater potential for MIB-related off-flavor problems at high feed application rates. The microbial sources responsible for production of geosmin and MIB in the culture tanks remain unknown.     

Expanded geographical distribution of Myxobolus cerebralis: first detections from Alaska

The parasite responsible for salmonid whirling disease, Myxobolus cerebralis, was introduced to the USA in 1958. It has since spread across the country causing severe declines in wild trout populations, but has never been documented from Alaska. However, while assessing the risk of introduction of M. cerebralis into the state, we detected the parasite using a species-specific polymerase chain reaction (PCR) assay. Testing of 180 hatchery rainbow trout, Oncorhynchus mykiss (Walbaum), by pepsin trypsin digest (PTD) and quantitative PCR (QPCR) revealed 14 positive samples. Infection was confirmed by sequencing the parasite 18S rRNA gene and by a nested PCR assay based on the same gene. Sequence comparison of M. cerebralis from several locations demonstrated the Alaska isolates were genetically distinct and therefore not false-positives arising from contamination during processing. We were unable to visually identify myxospores, indicating that either infection was light or mature spores had not formed. A reference set of fish samples spiked with known numbers of myxospores verified the QPCR and PTD results. This paper presents DNA sequence data from the Alaska M. cerebralis isolates, provides a brief history of the fish and facility of origin, and discusses implications of different testing methods on asymptomatic fish populations.