Effects of formalin on total haemocytes count and histopathological changes in the shrimp Litopenaeus schmitti (Pérez‐Farfante & Kensley 1997)

Formalin is used in shrimp industry to eliminate ectoparasites and as a disinfectant. However, the effect of formalin on shrimp's defense mechanism is unknown. Several biomarkers were used to assess the immune response of juveniles of the shrimp Litopenaeus schmitti exposed to different concentrations of formalin (10, 25 and 50 mg L^?1) during 24 and 48 h. Formalin concentrations of 25 and 50 mg L^?1 produced a significant reduction in the total haemocyte count at both 24 and 48 h. Peroxidase and phenoloxidase activity did not show variations. The total protein concentration in haemolymph of shrimps was not significantly different between experimental groups. Histological analysis showed hyperplasia in the gills of animals exposed at 10 mg L^?1 for 24 h; however, the exposure at 25 and 50 mg L^?1 caused necrosis in gills, hepathopancreas and the antennal gland.     

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.     

The pond's shape matters: differential growth,physiological condition and survival of epibenthic Farfantepenaeus aztecus postlarvae

As a function of the water quality provided by square, circular and oval experimental ponds, the growth, survival and oxygen requirements in epibenthic postlarvae of Farfantepenaeus aztecus were analysed in relation to their routine metabolism and apparent heat increment. Temperature, oxygen concentration, pH and salinity were measured daily in two experimental ponds of each shape. The postlarvae oxygen consumption during two 24‐h cycles, their growth, physiological condition and survival and the productivity in the ponds were estimated. Low values of pH, oxygen concentration and phytobenthos productivity, and reduced postlarvae relative growth and survival were observed in the square ponds. We suggest that the latter results from a deficient water circulation related to the effect of the pond's shape on dissolved oxygen levels and, consequently, on growth and survival. The postlarvae routine metabolism, including feeding, varied between 1.91 and 2.25 mg O₂ h^?1 g^?1 wet weight, whereas the minimum oxygen concentration needed in the ponds is approximately 4.25 mg O₂ L^?1. These conditions were achieved in the oval ponds concurrent with higher survival and growth values, in which individuals distributed randomly, for which we suggest that oval‐shaped ponds could be the most adequate for the culture of this and other penaeid species.     

Evaluating eddy covariance cotton ET measurements in an advective environment with large weighing lysimeters

Eddy covariance (EC) systems are being used to assess the accuracy of remote sensing methods in mapping surface sensible and latent heat fluxes and evapotranspiration (ET) from local to regional scales, and in crop coefficient development. Therefore, the objective was to evaluate the accuracy of EC systems in measuring sensible heat (H) and latent heat (LE) fluxes. For this purpose, two EC systems were installed near large monolithic weighing lysimeters, on irrigated cotton fields in the Texas High Plains, during the months of June and July 2008. Sensible and latent heat fluxes were underestimated with an average error of about 30%. Most of the errors were from nocturnal measurements. Energy balance (EB) closure was 73.2–78.0% for daytime fluxes. Thus, daylight fluxes were adjusted for lack of EB closure using the Bowen ratio/preservation of energy principle, which improved the resulting EC heat flux agreement with lysimetric values. Further adjustments to EC-based ET included nighttime ET (composite) incorporation, and the use of ‘heat flux source area’ (footprint) functions to compensate ET when the footprint expanded beyond the crop field boundary. As a result, ET values remarkably matched lysimetric ET values, with a ‘mean bias error ± root mean square error’ of −0.03 ± 0.5 mm day⁻¹ (or −0.6 ± 10.2%).     

Response of apricot trees to deficit irrigation strategies

During four growing seasons, 10-year-old apricot trees (Prunus armeniaca L., cv. ‘Búlida’) were submitted to three different drip irrigation regimes: (1) a control treatment, irrigated at 100% of seasonal crop evapotranspiration (ETc), (2) a continuous deficit irrigation (DI) treatment, irrigated at 50% of the control treatment, and (3) a regulated deficit irrigation (RDI) treatment, irrigated at 100% of ETc during the critical periods, which correspond to stage III of fruit growth and 2 months after harvest (early postharvest), and at 25% of ETc during the rest of the non-critical periods in the first two growing seasons and at 40% of ETc in the third and fourth. Soil–plant–water relation parameters were sensitive to the water deficits applied, which caused reductions in leaf and soil water potentials. The longer and severer deficits of the RDI treatment decreased fruit yield in the first two seasons. The RDI treatment pointed to two threshold values that defined the level at which both plant growth and yield were negatively affected with respect to the control treatment: (1) a predawn leaf water potential of around −0.5 MPa during the critical periods, and (2) a 22% drop in irrigation water. The total yield obtained in the DI treatment was significantly reduced in all the years studied due to the lower number of fruits per tree. No changes in the physical characteristics of fruits were observed at harvest. RDI can be considered a useful strategy in semiarid areas with limited water resources.     

Insulin and IGF-I receptors and tyrosine kinase activity in carp ovaries: changes with reproductive cycle

Insulin and insulin-like growth factor I (IGF-I) receptors from carp ovaries were semipurified with wheat germ agglutinin at different moments of the reproductive cycle and their binding characteristics and tyrosine kinase activity were studied. Specific receptors for insulin and IGF-I were found. IGF-I receptors presented higher binding (23.8 ± 1.5%), number of receptors (965 ± 20fm/mg) and affinity (K_D 0.24 ± 0.03nM) than those shown for insulin receptors (4.1 ± 1%, 530 ± 85fm/mg and 0.85 ± 0.1nM, respectively). Insulin and IGF-I receptors have a tyrosine kinase activity which is not different from that found in muscle of the same species. Seasonal changes were found in binding, with maximum values for insulin and IGF-I reached at the end of pre-spawning period (June). However, while IGF-I binding was observed in all stages, insulin binding decreased in autumn and disappeared in winter, which suggests a different role for the two peptides in ovarian physiology.     

Design and validation of a RT‐qPCR procedure for diagnosis and quantification of most types of infectious pancreatic necrosis virus using a single pair of degenerated primers

Infectious pancreatic necrosis virus (IPNV) is an important virus which affects the salmonid aquaculture industry worldwide; therefore, it is important to develop rapid and reliable methods of diagnosis to detect the disease at early stages. Nowadays, RT‐qPCR is replacing other methods because it provides additional information on the viral load, which is important to have a better understanding of the virus replication level and of the stage of the infection and its risk level. The main problem stems from the high diversity of this virus, which can compromise the reliability of the diagnosis. In this study, we have designed an RT‐qPCR procedure for diagnosis and quantification of IPNV based on a single pair of primers targeted to segment B. The procedure has been validated, in vitro and in vivo, testing two different types of standards against seven reference strains and 23 field isolates from different types. The procedure is reliable for the detection of any type, with a detection limit of 31 TCID₅₀ mL^?1, 50 pfu mL^?1 or 66 RNA copies mL^?1, depending on the standard. All the standard curves showed high reliability (R² > 0.95). The results support the high reliability of this new procedure for the diagnosis and quantification of IPNV.     

Effects of Broomrape Parasitism on Sunflower Plants: Growth,Development, and Mineral Nutrition

Sunflower broomrape (Orobanche cumana Wallr.) is a parasitic plant that infects sunflower (Helianthus annuus L.) plants. In this work, sunflower plants were grown under greenhouse conditions in pots with the substrate infested or non-infested with broomrape seeds. At different numbers of days after sowing, plant height, internode lengths, number of leaves, head diameter, mineral composition of leaves, and potassium (K) concentration in stem were measured. The negative effects of broomrape parasitism were assessed from 57 d after sowing, when broomrape started to emerge. Parasitized plants exhibited lower shoot dry weight, height, and head diameter than control plants. The reduction in internode lengths was associated with a decrease in the gradient of K concentration from basal to apical stem. The mineral composition of leaves was also affected in parasitized plants. The concentrations of calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn) in leaves of parasitized plants were lower than those of the control plants, while there were few differences for K, phosphorus (P), iron (Fe), and copper (Cu). The effects of parasitism are discussed in relation to their competition for resources and to perturbations of the host physiology such as hormonal and water balance.     

MODELING GROWTH AND ION CONCENTRATION OF LILIUM IN RESPONSE TO NITROGEN:POTASSIUM:CALCIUM MIXTURE SOLUTIONS

Nutrient solution composition plays an important role in root uptake rate due to interactions among nutrients and internal regulation. Studies to determine the optimum nutrient solution concentration are focused on individual ions, ignoring the adaptation mechanisms triggered by plants when growing in a varying external nutrient concentration. The objective of the present study was to determine the response in growth and tissue ion concentration of lilium cv. ‘Navona’ to nutrient mixtures of varying proportions of nitrogen (N), potassium (K⁺), and calcium (Ca²⁺) in solution using mixture experiments methodology in order to determine the optimum concentration. Bulbs of lilium were transplanted in plastic crates and drip-irrigated with the treatment solutions, which consisted of a mixture of N, K⁺, and Ca²⁺ whose total concentration was 340 mg L^?1 and minimum concentrations of each ion was 34 mg L^?1. Chlorophyll concentration (SPAD), shoot fresh weight (FW), leaf FW, and leaf area were measured 60 days after transplanting and ion analysis was performed on shoot tissues from selected treatments. Lilium exhibited a moderate demand for N and K⁺ (136–170 mg L^?1 N and 116–136 mg L^?1 K⁺) and a very low demand for Ca²⁺ (34–88 mg · L^?1). This low demand may be due to the remobilization of the nutrients stored in the bulbs. Integrating the predictions of the models estimated to produce >90% of maximum growth, the optimum nutrient solution should contain Ca²⁺ at a concentration between 34 and 126 mg · L^?1, K⁺ between 119 and 211 mg · L^?1, and N between 92 mg · L^?1 and 211 mg · L^?1. Increasing external N concentration affected internal N concentration but not internal K⁺ or Ca²⁺ concentrations, despite that the increase in external N was associated with a decrease in external K⁺ and Ca²⁺. Similar trends were observed for external K⁺ and Ca²⁺ concentration. In conclusion, lilium was able to maintain a relatively constant K⁺ and Ca²⁺ concentration regardless of the lower concentration in the nutrient solution when N was increased (similar response was observed for K⁺ and Ca²⁺) and it has a low Ca²⁺ demand and moderate N and K⁺ supply.