Fish larvae: zooplankton relationships in microcosm simulations of earthen nursery ponds. II. brackish water system

A simulation of the effects of predation intensity on zooplankton composition in brackish water nursery ponds was carried out in order to address the problem that commercial fish nurseries encounter in obtaining enough zooplankton of adequate species composition and size when fish larvae start to feed. The experimental system consisted of twelve 130 l containers with treatments of four densities (0, 1, 2, or 4 larvae l⁻¹) of common carp (Cyprinus carpio L.), stocked on the 6th day after filling the containers. Zooplankton-environment relationships were explored using factor analysis. Factor analysis allowed identifying several groups of zooplankters that responded in different ways to fish larvae predation pressure. The first factor represented a general measurement of rotifer abundance, and the second identified the direct effect of size-selective fish predation. Since no rotifers were present in the filling water, all these species were autochthonous populations that hatched from resting forms in the sediment and reproduced. In the absence of fish predation, this led to a steep rotifer increase. Fish predation started when the rotifer concentration was just starting to increase and their direct predation reduced and delayed the rotifer abundance peak. This effect increased with the increase in fish larvae density. Estimations of rotifer consumption by fish larvae in this experiment were higher than similar calculations from data of the literature, which led us to test the hypothesis that factors other than direct predation were affecting rotifer population dynamics. The mechanisms involved in rotifer population regulation are discussed. It was concluded that in commercial nurseries, increased larvae production can be achieved by keeping the larvae density at an intermediate level and stocking fish to match the increasing phase of the rotifer peak. Under reasonable larvae density (up to 2 l⁻¹) it seems that the direct predation effect of fish larvae on rotifer dynamics is minor, compared to fish induced self regulation.     

Thermal preference and tolerance of green abalone Haliotis fulgens (Philippi, 1845) and pink abalone Haliotis corrugata (Gray, 1828)

The thermoregulatory behaviour of green abalone Haliotis fulgens and pink abalone H. corrugata was investigated. Haliotis fulgens juveniles ranging in wet weight from 3.0 to 3.3 g and from 28.7 to 30.5 mm shell length and of H. corrugata 2.0 g and 25.7 mm in shell length were exposed to 19°C for 30 days in a flow‐through water system. Temperature preference was determined in a horizontal thermal gradient and was found to be 25.4°C for green abalone and 25.0°C for pink abalone. Displacement velocity was 4.3 cm h⁻¹ for H. fulgens and 12.8 cm h⁻¹ for H. corrugata. The optimum temperature for growth calculated for both abalone species was 24.6 and 24.5°C respectively. The critical thermal maxima (CTMax) of H. fulgens and H. corrugata were determined as a measure of thermal tolerance. Abalones were subjected to increasing water temperatures at a rate of 1°C on 30 min until they detached from the substrate. The CTMax at 50% were 33.6 and 32.0°C for green and pink abalone respectively. The results are discussed in relation to site selection and commercial rearing.     

Historical and contemporary habitat use of sperm whales around the Galápagos Archipelago: Implications for conservation

1. Sperm whales have occupied the waters off the Galápagos Islands, Ecuador, for at least the past 200 years. During the 19^th century, they were the target of intensive whaling that severely depleted the population. In recent times, after commercial whaling ended, sperm whales in the region remain vulnerable to multiple threats, especially potential entanglement in fishing gear, which may hinder their ability to recover from the whaling era.
2. As a highly mobile, long-lived species, long-term analysis of the habitat use of sperm whales is necessary to establish effective conservation and management strategies. Here, contemporary (1985–2014) and historical (1830–1850) sperm whale habitat use off the Galápagos Islands was analysed and contrasted to the extent of the Galápagos Marine Reserve (GMR). Contemporary habitat use and its variability over time were modelled as a function of geographic, oceanographic, and topographic variables using generalized additive models.
3. The fine-scale habitat (<50 km) used by sperm whales was associated with topographic (i.e. depth and slope) and oceanographic characteristics (i.e. relative sea surface temperature and standard deviation of sea surface temperature), but these preferences varied over time.
4. While historical and contemporary data indicate that sperm whale habitat primarily occurred within the boundaries of the GMR, in recent years, whales were found up to 30.1% of the time outside the GMR, potentially overlapping with commercial fisheries operating in the area.
5. The dynamic nature of the relationship of this nomadic species with its habitat highlights the need of large-scale conservation efforts across the Eastern Tropical Pacific region, including the wide-scale enforcement of regulations requiring the use of Automatic Identification System in fishing vessels, the promotion of on-board fisheries observer programmes, the development of adaptive management strategies, and international collaboration to identify and mitigate threats.

     

Mate choice of an endogeic earthworm revealed by microsatellite markers

Endogeic earthworms are difficult study subjects due to the cryptic medium in which they live; thus, only the behaviour of epigeic and anecic earthworms has been studied before. We used microsatellite markers as a tool to elucidate the mate choice processes of Hormogaster elisae, an endogeic earthworm. It was shown to normally mate with two partners, preferably of the same size that are found in close proximity thereby eliminating the need for long-distance dispersion, which could explain the previously observed high genetic differentiation between populations. The genetic analyses of the sperm within each of its four spermathecae showed a uniform distribution with no signs of differential storage of sperm from different partners.     

Improved husbandry to control an outbreak of rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum

CASE DESCRIPTION: A cohort of 35,200, 13-week-old, female rainbow trout at a fish farm was evaluated because of a 2-week history of anorexia and lethargy and a mortality rate of approximately 100 fish/d. CLINICAL FINDINGS: Affected fish were lethargic and thin and had disequilibrium, bilateral exophthalmia, pale red gills and kidneys, red-tinged coelomic fluid, and pale brown livers. Some fish were differentially pigmented bilaterally. The presumptive diagnosis was bacterial or viral septicemia. The definitive diagnosis was rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum. TREATMENT AND OUTCOME: A strategy for controlling the outbreak based on reducing pathogen numbers in affected tanks and reducing pathogen spread among tanks was developed. The option of treating with antimicrobial-medicated feed was discussed with the farmer, but was declined. After changes were made, mortality rate declined quickly, with no more deaths within 10 days after the initial farm visit. CLINICAL RELEVANCE: Bacterial coldwater disease is the most common manifestation of infection with F psychrophilum in fingerling and adult rainbow trout. However, the organism can also cause rainbow trout fry syndrome. This condition should be included on a list of differential diagnoses for septicemia in hatchery-reared rainbow trout fry.     

Cytogenetic variation in somatic tissue cultures and regenerated plants of barley (Hordeum vulgare L.)

Summary Chromosome number of morphogenic and non-morphogenic calli and regenerated plants of barley were determined. Cultures were obtained from two kinds of explants, immature embryos and seedling leaves from three cultivars, Ingrid, Dissa and Golden Promise. Callus chromosome analyses were carried out during a 12 month period in a medium containing 2 mg/l of 2,4-D. Diploid cells were predominant in all cases; although in leaf-derived cultures, retraploid cells (2n=4x=28) showed a tendency to increase as time in culture increased and after more than six months in culture, diploid cells decreased to percentages of almost 70%. Aneuploid cells were generally infrequent in all cases. The source of explant has been more important than the genotype (cultivar) and the type of callus (morphogenic vs. non-morphogenic) in the chromosomal stability of cultures as time increases. From short term cultures, only 1.85% of the regenerated plants were tetraploid, the remaining were diploids. The ability of morphogenic calli to regenerate plants decreased before any significant reduction of diploid cells were observed.     

Analysis of genetic relationships among 22 European barley varieties based on two PCR markers

Two long primers of 19 (F17) and 20 (F13) nucleotides, respectively,were used in polymerase chain reactions to amplify DNA from differentcultivated barley accessions. These primers can distinguish closely relatedvarieties and, with a unique primer, all the barley accessions analysedshowed a characteristic fingerprint. Sixty per cent and 76% of thefragments generated using F13 and F17, respectively, were polymorphic.The genetic similarity values between accessions were estimated from F13and F17 data. The dendrogram and principal coordinate analysis performedwith F13 data revealed a clear separation of these varieties in accord withtheir pedigree relationships.     

Nutrient Loading by Precipitation in the Maracaibo Lake Basin, Venezuela

Nutrient content and pH of rain samples collected at nine sites during 1988-1996 were studied to determine the amounts of N, P and S added by precipitation over Maracaibo Lake basin. The basin is a wide depression occupied by Lake Maracaibo and extensive alluvial plains and delimited by a mountainous zone of variable physiolgraphic characteristics with different cattle ranching and industrial activities. Rain pHs averaged ≈ 4 to 6, individual samples occasionally reached as low as pH 3 in the south basin. NH₄ ⁺ levels were significantly higher (up to 2.6 mg/l NH₄-N) than NO₃ ^? plus NO₂ ^?. Phosphorus levels were low, ranging from undetectable to 1.5 mg/l. The amounts of inorganic N/ha/yr added ranged from ≈ 5.4 Kg in the north to ≈ 8 Kg in the south basin; around the lakeshore, it was estimated that ≈ 9.8–16.8 Kg TN/ha (≈ 55 % as organic-N) are annually deposited. The annual amounts of SO₄-S/ha added range from ≈ 10 to 13 Kg. The contribution of precipitation to P in the ecosystem is very small; ≈ 0.02 – 0.8 Kg of PO₄-P/ha/yr was added in basin. The results of this study show that precipitation represents a significant factor for the total nitrogen and sulfur loading to Maracaibo Lake Basin.     

Phenolic profile of quince fruit (Cydonia oblonga Miller) (pulp and peel)

Qualitative and quantitative analyses of phenolic compounds were carried out on quince fruit samples from seven different geographical origins in Portugal. For each origin, both pulp and peel were analyzed by reversed-phase HPLC-DAD and HPLC-DAD/MS.The results revealed differences between the phenolic profiles of pulps and peels in all studied cases. The pulps contained mainly caffeoylquinic acids (3-, 4-, and 5-O-caffeoylquinic acids and 3,5-dicaffeoylquinic acid) and one quercetin glycoside, rutin (in low amount). The peels presented the same caffeoylquinic acids and several flavonol glycosides: quercetin 3-galactoside, kaempferol 3-glucoside, kaempferol 3-rutinoside, and several unidentified compounds (probably kaempferol glycoside and quercetin and kaempferol glycosides acylated with p-coumaric acid). The highest content of phenolics was found in peels.