Neon Tetra Research Articles

The Mechanism of Color Change in the Neon Tetra Fish: a Light‐Induced Tunable Photonic Crystal Array

AbstractThe fresh water fish neon tetra has the ability to change the structural color of its lateral stripe in response to a change in the light conditions, from blue‐green in the light‐adapted state to indigo in the dark‐adapted state. The colors are produced by constructive interference of light reflected from stacks of intracellular guanine crystals, forming tunable photonic crystal arrays. We have used micro X‐ray diffraction to track in time distinct diffraction spots corresponding to individual crystal arrays within a single cell during the color change. We demonstrate that reversible variations in crystal tilt within individual arrays are responsible for the light‐induced color variations. These results settle a long‐standing debate between the two proposed models, the “Venetian blinds” model and the “accordion” model. The insight gained from this biogenic light‐induced photonic tunable system may provide inspiration for the design of artificial optical tunable systems.

The mechanism of color change in the neon tetra fish: a light-induced tunable photonic crystal array.

The fresh water fish neon tetra has the ability to change the structural color of its lateral stripe in response to a change in the light conditions, from blue-green in the light-adapted state to indigo in the dark-adapted state. The colors are produced by constructive interference of light reflected from stacks of intracellular guanine crystals, forming tunable photonic crystal arrays. We have used micro X-ray diffraction to track in time distinct diffraction spots corresponding to individual crystal arrays within a single cell during the color change. We demonstrate that reversible variations in crystal tilt within individual arrays are responsible for the light-induced color variations. These results settle a long-standing debate between the two proposed models, the "Venetian blinds" model and the "accordion" model. The insight gained from this biogenic light-induced photonic tunable system may provide inspiration for the design of artificial optical tunable systems.

Magnetic control of the inclination of biogenic guanine crystals fixed on a substrate

In the present study, we describe the fabrication and manipulation of a micro-mirror system similar to the iridophores of neon tetra that allow microstructural light control. Biogenic guanine crystals as micro-mirrors were adhered to a glass substrate with flexible DNA joints under a vertical magnetic field of 480 mT. We then observed the movement of the micro-mirrors under sub-Tesla horizontal magnetic fields. Under ambient fields, the orientation of the guanine micro-mirrors did not change. Appling a horizontal magnetic field of approximately 400 mT generated by an electromagnet induced motion and width changes of the guanine micro-mirrors, which were observed by an optical microscope. However, the inclination of the micro-mirrors recovered upon removal of the magnetic field. The developed guanine micro-mirrors on a glass substrate demonstrate the remote control of microstructural diamagnetic materials, and may show promise for use as an underwater microactuator for microfluidic systems.

A method for resolving occlusions when multitracking individuals in a shoal.

Studying the collective behavior of fishes often requires tracking a great number of individuals. When many fishes move together, it is common for individuals to move so close to each other that some fishes superimpose themselves on others during one or several units of time, which impacts on tracking accuracy (i.e., loss of fish trajectories, interchange of fish identities). Type 1 occlusions arise when two fishes swim so near each other that they look like one long fish, whereas type 2 occlusions occur when the fishes' trajectories cross to create a T- or X-shaped individual. We propose an image processing method for resolving these types of occlusions when multitracking shoals in two dimensions. We assessed processing effectiveness after videorecording shoals of 20 and 40 individuals of two species that exhibit different shoal styles: zebrafish (Danio rerio) and black neon tetras (Hyphessobrycon herbertaxelrodi). Results show that, although the number of occlusions depended on both the number of individuals and the species, the method is able to effectively resolve a great deal of occlusions, irrespective of the species and the number of individuals. It also produces images that can be used in a multitracking system to detect individual fish trajectories. Compared to other methods, our approach makes it possible to study shoals with water depths similar to those seen in the natural conditions of the two species studied.

Cutaneous infection with Dermocystidium salmonis in cardinal tetra, Paracheirodon axelrodi (Schultz, 1956).

The genus Dermocystidium comprises fungal pathogens of the order Dermocystida in the class Ichthyosporea (http://www.ncbi.nlm.nih.gov/taxonomy). Several different Dermocystidium species have been described, infecting a variety of fish hosts and producing gill infections, skin lesions and visceral disease all over the world (Wildgoose 1995; Pekkarinen & Lotman 2003; Pekkarinen et al. 2003; Feist et al. 2004; Zhang & Wang 2005). To our knowledge, there are two reports on Dermocystidium infections in cardinal tetra, Paracheirodon axelrodi and neon tetra, Paracheirodon innesi (Reichenbach-Klinke 1982; Lewisch 2010). However, these reports did neither include histological and ultrastructural examinations nor molecular genetic investigations to confirm the diagnosis and identify the aetiologic species. In January 2013, increased mortalities of cardinal tetra, P. axelrodi of a 350-L aquarium were reported, occurring after purchase of additional fish. During the clinical examination, most of the fish were swimming in normal active condition, but some were lethargic or displayed a transparent mass on the skin of the head or body. The masses were up to 5 mm in diameter and contained a central, white tubular structure. Similar masses were located on the fins of some fish, but were considerably smaller in these locations. A parasitic infestation of the skin of these fish was excluded via microscopic examination, and normal results were obtained after analysis of the water values and inspection of the pump and filter system. Six cardinal tetra, P. axelrodi and two firehead tetra, Hemigrammus bleheri were submitted for pathological examination in formalin and for molecular genetic examination in ethanol. Only two cardinal tetra displayed skin lesions. Before embedding, one tetra was post-fixed in Davidson’s fixative and sections of glycolmethacrylate/methylmethacrylate-embedded samples were routinely processed for histological examination and stained with haematoxylin and eosin (HE), Giemsa, silver impregnation and periodic acid Schiff (PAS) reaction according to standard protocols. Samples of the mass were also routinely processed for transmission and scanning electron microscopy on a transmission electron microscope (Zeiss EM 10) or on a digital scanning electron microscope (Zeiss DSM 950), respectively. The macroscopic examination of the cardinal tetra revealed a focally extensive, bulging, hemispherical, transparent oedema (4 mm in diameter) of the ventral skin on the head. Central, within Correspondence M C Langenmayer, Institute of Veterinary Pathology at the Centre for Clinical Veterinary Medicine, LMU Munich, Veterin€ arstrasse 13, 80539 Munich, Germany (e-mail: langenmayer@patho.vetmed.uni-muenchen.de) Langenmayer and Lewisch contributed equally to this work.

Effect of Green Water and Mixed Zooplankton on Growth and Survival in Neon Tetra, Paracheirodon innesi (Myers, 1936) during Larval and Early Fry Rearing

Effect of Green Water and Mixed Zooplankton on Growth and Survival in Neon Tetra, Paracheirodon innesi (Myers, 1936) during Larval and Early Fry Rearing

Dietary Influence of Amino Acids on Growth of Neon tetraParacheirodon innesi

A study was conducted to determine the effect of dietary amino acids on the growth performance of neon tetra (Paracheirodon innesi). Eleven purified diets were prepared using crystalline amino acids, and their effects on growth, survival and feed performance of P. innesi (0.0506±0.001 g mean initial weight) were evaluated. Control diet contained all ten essential amino acids, while in other diets one essential amino acid was deleted and that amino acid was replaced with alanine. Fishes were fed by hand to apparent satiation, twice a day, for 90d. Fish fed with the control diet resulted in the highest weight gain, specific growth rate, food conversion efficiency and protein efficiency ratio and it differed significantly (P<0.05) with other diets. This indicated that all ten amino acids were found essential for growth of P. innesi. Lowest growth was observed in lysine, arginine, leucine, valine and threonine deficient diets. From the growth data, it was evident that the growth rate reduced in absence of each of the chosen amino acids and it thus proved that they were more essential for this species. It is concluded that appropriate and balanced incorporation of each amino acid in the diet of P. innesi is necessary for the efficient feed utilization and better growth for its mass production.

INVOLVEMENT OF MICROBIAL MATS IN DELAYED DECAY: AN EXPERIMENTAL ESSAY ON FISH PRESERVATION

Microbial mats have been implicated in exceptional fossil preservation. Few analyses have addressed how these complex-multilayered biofilms promote fossil preservation. The sequence of changes during decay of neon tetra fish were tracked up to 27 months, and their decomposition in mats was compared against nonmat sediments (control fish). Statistically significant differences in quantitative variables (length, width, and thickness) are provided (ANOVA test, in all cases, P, 0.001). Changes in the qualitative features (body-head, fins, scale connection, and eye and body coloration) were phenetically analyzed resulting in two clusters and highlighting that notable differences in decay began at day 15. Mat fish how a delayed decomposition maintaining the external and internal body integrity, in which soft organs were preserved after 27 months as shown by Magnetic Resonance Imaging. We discuss how the organization, structure, and activity of this community are interrelated, favoring exceptional preservation. Microbial mats entomb the fish from the earliest stages, forming a Ca-rich coat over the carcass while embedding it in an anoxic condition. This quick entombment provides important protection against abiotic and/or biotic agents.

Additional novel Cryptosporidium genotypes in ornamental fishes

Current knowledge on the prevalence and genotypes of Cryptosporidium in fishes is still limited. This study investigated the prevalence of Cryptosporidium species in 171 ornamental fishes, belonging to 33 species, collected from 8 commercial aquariums around Perth, Western Australia. All samples were screened by nested PCR targeting the 18S rRNA locus. A total of 6 positives were identified by PCR at the 18S locus from 4 different species of fishes (red eye tetra, Moenkhausia sanctaefilomenae; gold gourami, Trichogaster trichopterus; neon tetra, Paracheirodon innesi; goldfish, Carassius auratus auratus), giving an overall prevalence of 3.5% (6/171). Four different genotypes were identified, only one of which has been previously reported in fish; piscine genotype 4 in a neon tetra isolate, a rat genotype III-like isolate in a goldfish, a novel genotype in three isolates from red eye (piscine genotype 7) which exhibited a 3.5% genetic distance from piscine genotype 1 and a piscine genotype 6-like from a gold gourami (1% genetic distance). Further biological and genetic characterisation is required to determine the relationship of these genotypes to established species and strains of Cryptosporidium.

8 Class Pets + 1 Squirrel ÷ 1 Dog = Chaos (review)

Reviewed by: 8 Class Pets + 1 Squirrel ÷ 1 Dog = Chaos Jeannette Hulick Vande Velde, Vivian . 8 Class Pets + 1 Squirrel ÷ 1 Dog = Chaos; illus. by Steve Björkman. Holiday House, 2011. [80p]. ISBN 978-0-8234-2364-4 $15.95 Reviewed from galleys R Gr. 2-4. When sassy squirrel Twitch is threatened by an owl, the open door of the nearby elementary school seems like a godsend. The principal's dog (over whose nose Twitch has trampled in his escape from the owl) thinks otherwise, though, so the chase is then on, and Twitch darts in and out of every classroom in the building trying to keep out of the indignant dog's grasp while enlisting aid from various class pets (each of whom narrates a chapter) in the process. That turns out to be a surprisingly successful recipe for a middle-grades novel; the storytelling is smart and snappy, and the tone is highly humorous. Additionally, each pet's narrative voice is both entertaining in its individuality and faithful to that animal's characteristics: the third-grade class' neon tetras, for example, keep repeating (somewhat mindlessly) "We are in a school," while the science-lab geckos speak alternate lines ("NEWTON: Sometimes we get mangoes. I like mangoes. GALILEO: I know you do. I prefer [End Page 174] the houseflies, which are crunchier. NEWTON: But not as sweet"), and the fifth grade's corn snake favors words with sibilant syllables ("Sneaky and slithery, yes. But stroke my skin and see: I'm not the slightest bit slimy"). Björkman's slightly scratchy black-and-white illustrations effectively echo the text's light, comic tone, and they successfully serve to punctuate, but never interrupt, the narrative flow. This will be an easy sell to animal lovers and those looking for a quick, funny read, but it also sits up and begs to be read aloud; creative adults and kids might also be able to develop it into a comedic readers' theater production. Copyright © 2011 The Board of Trustees of the University of Illinois

The effects of mixed-species assemblage on the behaviour and welfare of fish held in home aquaria

While there is growing scientific research into the welfare of fish held under aquaculture conditions, there has been little research into the welfare of ornamental fish kept in home aquaria. With the ever increasing popularity of home aquaria, there is now an urgent need to address our current lack of knowledge regarding welfare of mixed-species assemblages. Here we investigated the welfare of four commonly kept species of ornamental fish held in different species combinations and group sizes. Specifically we asked two questions (1) whether the presence of angelfish ( Pterophylum scalare) altered the behaviour of a mixed group of white cloud mountain minnows ( Tanichthys albonubes), neon tetras ( Paracheirodon innesi) and tiger barbs ( Barbus tetrazona) and (2) whether group size affected behaviour and welfare in a mixed group assemblage of angelfish, white cloud mountain minnows and neon tetras. Behaviours including intra and interspecific interactions (darting and aggressive attacks), shoaling, and use of environmental enrichment were measured. Angelfish appeared to have a beneficial effect on the welfare of small shoaling species by reducing aggression but had little effect on other behaviours. For white cloud mountain minnows and neon tetras, larger group sizes resulted in increased natural behaviours (i.e. a tendency to shoal). Interestingly, the present study highlighted the problems in predicting the effects of environmental enrichment with both species and group size altering the way enrichment was used (e.g. as shelter from competitors or as a resource worth aggressively defending). Setting scientifically determined guidelines on appropriate species assemblages or stocking densities for ornamental fish is challenged by the plethora of group sizes and combinations found within home aquaria; research as in the present study serves to provide insights into welfare issues which may not become apparent within unrepresentative, single-species studies.

Imitation of variable structural color in paracheirodon innesi using colloidal crystal films

Spacing variation of adjoining reflecting thin films in iridophore is responsible for the variable interference color in the paracheirodon innesi. On the basis of this phenomenon, colloidal crystal thin films with different structures are fabricated from monodisperse poly(styrene-methyl methacrylate-acrylic acid) (PSMA) colloids. The relationship between the colors and structures of the films is investigated and discussed according to the principle of light interference. A two-layer colloidal film having uniform color is researched and it displays diverse colors before and after swelling by styrene (St), which can be used to mimic the variable structural color of the paracheirodon innesi.

Pleistophora hyphessobryconis (Microsporidia) infecting zebrafish Danio rerio in research facilities

Zebrafish Danio rerio are important models for biomedical research, and thus, there is an increased concern about diseases afflicting them. Here we describe infections by Pleistophora hyphessobryconis (Microsporidia) in zebrafish from 3 laboratories. As reported in other aquarium fishes, affected zebrafish exhibited massive infections in the skeletal muscle, with no involvement of smooth or cardiac muscle. In addition, numerous spores within macrophages were observed in the visceral organs, including the ovaries. Transmission studies and ribosomal RNA (rRNA) gene sequence comparisons confirmed that the parasite from zebrafish was P. hyphessobryconis as described from neon tetra Paracheirodon innesi. Ten 15 d old zebrafish were exposed to P. hyphessobryconis collected from 1 infected neon tetra, and 7 of 10 fish became infected. Comparison of P. hyphessobryconis small subunit rRNA gene sequence from neon tetra with that obtained from zebrafish was nearly identical, with < 1% difference. Given the severity of infections, P. hyphessobryconis should be added to the list of pathogens that should be avoided in zebrafish research facilities, and it would be prudent to avoid mixing zebrafish used in research with other aquarium fishes.

Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

The structural colour of the neon tetra is distinguishable from those of, e.g., butterfly wings and bird feathers, because it can change in response to the light intensity of the surrounding environment. This fact clearly indicates the variability of the colour-producing microstructures. It has been known that an iridophore of the neon tetra contains a few stacks of periodically arranged light-reflecting platelets, which can cause multilayer optical interference phenomena. As a mechanism of the colour variability, the Venetian blind model has been proposed, in which the light-reflecting platelets are assumed to be tilted during colour change, resulting in a variation in the spacing between the platelets. In order to quantitatively evaluate the validity of this model, we have performed a detailed optical study of a single stack of platelets inside an iridophore. In particular, we have prepared a new optical system that can simultaneously measure both the spectrum and direction of the reflected light, which are expected to be closely related to each other in the Venetian blind model. The experimental results and detailed analysis are found to quantitatively verify the model.

The effect of group size on the behaviour and welfare of four fish species commonly kept in home aquaria

Previous research into fish welfare has focussed particularly on commercially important aquaculture species. However, with over 350 million fishes traded annually within the ornamental fish industry, surprisingly little consideration has been given to the welfare of fish kept in home aquaria. Here, the welfare of four commonly kept species of ornamental fish (neon tetras, white cloud mountain minnows, angelfish and tiger barbs) was investigated in relation to group size. Behaviours including darting, aggression, shoaling and latency to feed were found to vary with group size in a species-specific manner. Neon tetras and white cloud mountain minnows displayed reduced aggression and darting and spent more time shoaling in larger groups. Behavioural patterns were more variable in angelfish and tiger barbs although larger group sizes resulted in increased shoaling. Principal components analysis of the behaviour scores obtained indicated improved welfare in larger groups of neon tetras, white cloud mountain minnows and tiger barbs with no clear link between welfare and group size in angelfish. In conclusion, although the effect of group size on the behaviour of ornamental fish species is species-specific, combination of behavioural parameters within a principal components analysis allows group sizes that promote improved welfare to be identified.

The Reproduction of Neon Tetra, &lt;i&gt;Paracheirodon Innesi&lt;/i&gt; (Myers, 1936), Under Controlled Conditions

A study on reproduction of neon tetra has been carried out under controlled conditions. Neon tetra is very popular aquarium fish. It was observed that spawners of this species produce viable gametes during a few (5–6) spawning periods only. From the breeding perspective fish of that species should be reproduced again shortly after the completed spawning and time between spawns should be 15 to 20 days. Keeping the fish between spawning periods more than 20 days results in a significant deterioration of quality of gametes, expressed by the decreased number of 12-day-old larvae. It was shown that before spawning spawners should be kept in water at 22 o C. The negative effect of keeping

Snout Chondroma in a Neon Tetra Paracheirodon innesi

An adult neon tetra Paracheirodon innesi with a history of difficulty in feeding caused by a mass overwhelming the snout is presented. Macroscopically the fish presented a unilateral, single, nodular and well-circumscribed, perlaceous, firm to hard mass in the left snout region. Histologically, tumor tissue was formed mainly by abundant, highly cellular elliptic nests of chondro- cytes lying in mature hyaline cartilage matrix. Besides this component there were bubbly appearing large cells (physaliphorous-like cells) and a minority of cells having well defined cytoplasmic boundaries, clear eosinophilic pale cytoplasm and a rounded centrally located nucleus (fried egg-like cells). Alcian-PAS and Masson's trichrome stains were applied to demonstrate proteoglycans and colla- gen of the matrix. Based on topographic localization and histomorphological features, a diagnosis of snout chon- droma was made. This case can be added to the other rare spontaneous cartilage tumors of fish described in literature.

Why is the neon tetra so bright? Coloration for mirror-image projection to confuse predators? “Mirror-image decoy” hypothesis

The neon tetra (Paracheirodon innesi), which inhabits blackwater streams of the Amazon basin, has extremely bright coloration characterized by metallic blue-green stripes. To clarify the ecological function of this coloration, we examined the appearance of living neon tetra. They changed color in response to lighting and background conditions, and became less conspicuous under each condition to the human eye. Although they appeared bright in colorless clear water, their stripes appeared darker in blackwater. In addition, the visible area of their stripes was small and their brightness decreased, unless they were observed within a limited viewing angle (approximately 30° above the horizon). The results show that from the viewpoint of approaching submerged predators, a bright mirror image of the stripes is projected onto the underside of the water’s surface, providing a dramatic visual target while the real fish remains less conspicuous. Based on these results, we hypothesize that the neon tetra’s bright coloration is an effective predator evasion strategy that confuses predators using bright mirror images.

Dietary Protein Source and Level Affects Growth in Neon Tetras

AbstractNutritional studies for aquarium fishes like the neon tetra Paracheirodon innesi are sparse in comparison with those for food fish. To determine the optimum dietary protein level and source for growth of neon tetras, diets were formulated to contain 25, 35, 45, and 55% dietary protein from either marine animal protein or plant protein sources in a 4 × 2 factorial treatment design. Neon tetras (initial weight, approximately 0.12 g) were reared in 5‐L fiberglass tanks (25 fish/tank, 3 tanks/diet) in a freshwater recirculating system. Fish were hand‐fed the experimental diets three times per day for 12 weeks. Average weight gain of neon tetras fed diets with marine protein sources was significantly higher than that for fish fed diets based on plant proteins. Fish fed diets containing 45% or 55% crude protein had significantly greater weight gain than did fish fed 25% crude protein from either protein source. Fish fed 25% crude protein from either source had a significantly higher feed conversion ratio than did those fed 45% or 55% crude protein. Survival ranged from 71% to 84% and was not significantly altered by dietary protein source or level. No significant interactions between dietary protein source and level were found for any of the response variables. As the price of fish meal continues to increase, the formulations of feeds for food fish will probably contain lower amounts of fish meal and higher amounts of plant protein products. If a similar trend occurs for ornamental fish diets, further refinement of nutritional requirements and assessment of palatability of feed ingredients for neon tetras and other aquarium species will be required.

Seventy-five-million-year-old tropical tetra-like fish from Canada tracks Cretaceous global warming

Newly discovered fossil fish material from the Cretaceous Dinosaur Park Formation of Alberta, Canada, documents the presence of a tropical fish in this northern area about 75 million years ago (Ma). The living relatives of this fossil fish, members of the Characiformes including the piranha and neon tetras, are restricted to tropical and subtropical regions, being limited in their distribution by colder temperatures. Although characiform fossils are known from Cretaceous through to Cenozoic deposits, none has been reported previously from North America. The modern distribution of characiforms in Mexico and southern Texas in the southernmost United States is believed to have been the result of a relatively recent colonization less than 12 Ma. The new Canadian fossils document the presence of these fish in North America in the Late Cretaceous, a time of significantly warmer global temperatures than now. Global cooling after this time apparently extirpated them from the northern areas and these fishes only survived in more southern climes. The lack of early Cenozoic characiform fossils in North America suggests that marine barriers prevented recolonization during warmer times, unlike in Europe where Eocene characiform fossils occur during times of global warmth.