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Cichlids offer an exciting opportunity to understand vertebrate speciation; chemical communication could be one of the drivers of African cichlid radiation. Chemical signals mediate key aspects in the lives of vertebrates and often are species-specific. Dominant male Mozambique tilapia (Oreochromis mossambicus Peters 1852) release a sex pheromone, 5β-pregnan-3α,17α,20β-triol 3-glucuronate and its 20α-epimer, via their urine. The objective of this study was to assess sensitivity, specificity and versatility of the olfactory system of O. mossambicus to other steroids and their conjugates using the electro-olfactogram. O. mossambicus was sensitive to several 3-glucuronidated steroids, but did not respond to prostaglandins, unconjugated steroids or 17- or 20-conjugated steroids. Stimulation of the olfactory epithelium with increasing concentrations (10-12 M to 10-5 M) of 5β-pregnan-3α,17α,20β-triol 3-glucuronate, 5β-pregnan-3α,17α,20α-triol 3-glucuronate, 3α,17α-dihydroxy-5β-pregnan-20-one 3-glucuronate, etiocholanolone 3α-glucuronate and 17β-estradiol 3-glucuronate produced characteristic sigmoidal concentration-response curves. However, tilapia were most sensitive to 17β-estradiol-3-glucuronate, which also had the lowest apparent EC50 and maximal response amplitude. Cross-adaptation and binary mixture experiments suggested that 5β,3α-reduced pregnan- and androsta- 3-glucuronates share (a) common olfactory receptor(s), whereas 17β-estradiol 3-glucuronate is detected via (a) distinct olfactory receptor(s). In conclusion, the Mozambique tilapia has evolved high olfactory sensitivity and specificity to 3-glucuronidated steroids through two distinct olfactory receptor types; one detecting a male sex pheromone and a second detecting 17β-estradiol 3-glucuronate, a putative female-derived signal. However, O. mossambicus differs much in its olfactory perception from the more recently derived East African cichlid Astatotilapia burtoni, suggesting that chemical communication could, indeed, be involved in speciation.
Blue catfish Ictalurus furcatus Lesueur, the largest catfish in North America, produces pectoral stridulation sounds (distress calls) when attacked and held. They have both fish and bird predators, and the frequency spectrum of their sounds is better matched to hearing of birds than to that of unspecialized fish predators with low frequency hearing. It is unclear whether their sounds evolved to function in air or water. We categorized the calls and how they change with fish size in air and water and compared developmental changes in call parameters with stridulation motions captured with a high-speed camera. Stridulation sounds consist of a variable series of pulses produced during abduction of the pectoral spine. Pulses are caused by quick rapid spine rotations (jerks) of the pectoral spine that do not change with fish size although larger individuals generate longer, higher amplitude pulses with lower peak frequencies. There are longer pauses between jerks, and therefore fewer jerks and fewer pulses in larger fish that take longer to abduct their spines and therefore produce a longer series of pulses per abduction sweep. Sounds couple more effectively to water (1400 times greater pressure in Pascals at 1m), are more sharply tuned and have lower peak frequencies than in air. Blue catfish stridulation sounds appear to be specialized to produce under-water signals although most of the sound spectrum includes frequencies matched to catfish hearing but largely above the hearing range of unspecialized fishes.
Derivation of a water quality guideline for aluminium in marine waters.
Environ Toxicol Chem. 2014 Oct 15;
Authors: Golding LA, Angel BM, Batley GE, Apte SC, Krassoi R, Doyle CJ
Abstract Metal risk assessment of industrialised harbours and coastal marine waters requires the application of robust water quality guidelines to determine the likelihood of biological impacts. Currently there is no such guideline available for aluminium in marine waters. A water quality guideline of 24 μg total Al/L has been developed for aluminium in marine waters based on chronic 10 % inhibition or effect concentrations (IC10 or EC10) and no observed effect concentrations (NOEC) from 11 species (2 literature values and 9 species tested including temperate and tropical species) representing 6 taxonomic groups. The three most sensitive species tested were a diatom Ceratoneis closterium (formerly Nitzschia closterium) (IC10=18 μg Al/L, 72-h growth rate inhibition) < mussel Mytilus edulis plannulatus (EC10=250 μg Al/L, 72-h embryo development) < oyster Saccostrea echinata (EC10=410 μg Al/L, 48-h embryo development). Toxicity to these species was caused by the dissolved aluminium forms of aluminate (Al(OH4 (-) ) and aluminium hydroxide (Al(OH)3 (0) ) while both dissolved and particulate aluminium contributed to toxicity in the diatom Minutocellus polymorphus and green alga Dunaliella tertiolecta. In contrast, aluminium toxicity to the green flagellate alga Tetraselmis sp. was due to particulate aluminium only. Four species, a brown macroalga (Hormosira banksii), sea urchin embryo (Heliocidaris tuberculata) and two juvenile fish species (Lates calcarifer and Acanthochromis polyacanthus), were not adversely affected at the highest test concentration used. Environ Toxicol Chem © 2014 SETAC.
PMID: 25318392 [PubMed - as supplied by publisher]
New disease records for hatchery-reared sturgeon. I. Expansion of frog virus 3 host range into Scaphirhynchus albus.
Dis Aquat Organ. 2014 Oct 16;111(3):219-27
Authors: Waltzek TB, Miller DL, Gray MJ, Drecktrah B, Briggler JT, MacConnell B, Hudson C, Hopper L, Friary J, Yun SC, Malm KV, Weber ES, Hedrick RP
Abstract In 2009, juvenile pallid sturgeon Scaphirhynchus albus, reared at the Blind Pony State Fish Hatchery (Missouri, USA) to replenish dwindling wild stocks, experienced mass mortality. Histological examination revealed extensive necrosis of the haematopoietic tissues, and a virus was isolated from affected organs in cell culture and then observed by electron microscopy. Experimental infection studies revealed that the virus is highly pathogenic to juvenile pallid sturgeon, one of several species of sturgeon currently listed as Endangered. The DNA sequence of the full length major capsid protein gene of the virus was identical to that of the species Frog virus 3 (FV3), the type species for the genus Ranavirus, originally isolated from northern leopard frog Lithobates pipiens. Although FV3 infections and epizootics in amphibians and reptiles are well documented, there is only 1 prior report of a natural infection of FV3 in fish. Our results illustrate the broad potential host range for FV3, with the known potential to cause significant mortality in poikilothermic vertebrates across 3 taxonomic classes including bony fishes, anuran and caudate amphibians, and squamate and testudine reptiles.
PMID: 25320034 [PubMed - in process]
Diversity of Bacteria Cultured from the Blood of Lesser Electric Rays Caught in the Northern Gulf of Mexico.
J Aquat Anim Health. 2014 Dec;26(4):225-232
Authors: Tao Z, Bullard SA, Arias CR
Abstract Abstract The prevalence and taxonomic diversity of bacteria cultured from the blood of apparently healthy Lesser Electric Rays Narcine bancroftii captured from open beach habitat in the north-central Gulf of Mexico are reported herein. The blood of 9 out of 10 Lesser Electric Rays was positive for bacteria, and bacterial isolates (n = 83) were identified by 16S rRNA gene sequencing. The majority of the isolates belonged to the phylum Proteobacteria (91.5%). Vibrio spp. comprised 53% of all isolates and were recovered from all Lesser Electric Rays with culture-positive blood. Among them, V. harveyi (n = 14) and V. campbellii (n = 11) were most common, followed by a group of unidentified Vibrio sp. (n = 10) related to V. nigripulchritudo. Isolates representing other species of Proteobacteria included Pseudoalteromonas (n = 13), Shewanella (n = 5), Amphritea (n = 3), Nautella (n = 3), and Arenibacter (n = 1). Higher bacterial diversity was observed in blood cultured on marine agar relative to blood agar, but gram-positive bacteria were isolated from the latter only. The 16S rRNA gene sequences of bacterial isolates were compared phylogenetically to those from related type strains. Most isolates were identified to the level of species, but some clustered independently from reference strains, likely representing new species of Vibrio, Amphritea, Shewanella, and Tenacibaculum. The present study is the first record of any bacterium from this ray species and reveals a taxonomically and phylogenetically diverse microbiota associated with its blood. Moreover, these data document that the presence of bacteria in elasmobranch blood is not coincident with clinical signs of disease, thereby rejecting the paradigm of septicemia indicating a disease condition in aquatic vertebrates. Received April 30, 2013; accepted April 16, 2014.
PMID: 25321403 [PubMed - as supplied by publisher]