Juvenile Killifish Research Articles

Mosaic Heterochrony in Neural Progenitors Sustains Accelerated Brain Growth and Neurogenesis in the Juvenile Killifish N.furzeri.

SummaryAlthough developmental mechanisms driving an increase in brain size during vertebrate evolution are actively studied, we know less about evolutionary strategies allowing accelerated brain growth. In zebrafish and other vertebrates studied to date, apical radial glia (RG) constitute the primary neurogenic progenitor population throughout life [1]; thus, RG activity is a determining factor of growth speed. Here, we ask whether enhanced RG activity is the mechanism selected to drive explosive growth, in adaptation to an ephemeral habitat. In post-hatching larvae of the turquoise killifish, which display drastic developmental acceleration, we show that the dorsal telencephalon (pallium) grows three times faster than in zebrafish. Rather than resulting from enhanced RG activity, we demonstrate that pallial growth is the product of a second type of progenitors (that we term NGPs for non-glial progenitors) that actively sustains neurogenesis and germinal zone self-renewal. Intriguingly, NGPs appear to retain, at larval stages, features of early embryonic progenitors. In parallel, RGs enter premature quiescence and express markers of astroglial function. Altogether, we propose that mosaic heterochrony within the neural progenitor population might permit rapid pallial growth by safeguarding both continued neurogenesis and astroglial function.

Extending international toxicity testing guidance to middle eastern test species.

The Arabian Gulf is a dynamic environment with unique habitats located in the Middle East. The inhabitants of this ecosystem have historically been understudied and a lack of reliable toxicity data exists to benchmark their sensitivities. Current international testing guidelines (i.e. Organization for Economic Co-Operation and Development (OECD), International Standard Organization (ISO), Environmental Protection Agency (EPA), etc.) do not reference relevant species for this region of the world. This research focuses on developing standard test conditions for relevant test organisms indigenous to the Middle East region while maintaining general agreement with international testing guidelines. A copepod, cyanobacteria and juvenile killifish were selected as local test organisms to perform acute exposures to 4 Aromatic Hydrocarbons (AHs) ranging in log KOW from 3.88-5.19, 1-methylnaphthalene, phenanthrene, biphenyl and octahydrophenanthrene. Acute test durations were 48, 72 and 96h and generally followed ISO 14669, OECD 201 and 203 for the copepod, algae and killifish respectively. To deliver and maintain controlled exposure concentrations, a passive dosing (PD) format was employed. PD effectively maintained aqueous exposure concentration of the AHs tested over the test duration. Effects data were comparable to literature values for similar taxonomic groupings. Critical target lipid body burden's for test species used were calculated and found to be in agreement with those predicted by the Target Lipid Model.

Larval prey selectivity of the lampeye killifish Aplocheilichthys spilauchen and its potential for mosquito biocontrol

Prey selectivity habit of a cyprinodontiform killifish, Aplocheilichthys spilauchen was investigated in the laboratory to assess its potential as a mosquito control agent. In three different experimental treatments, the fish was exposed to different proportions of mosquito and chironomid larvae. The extent of selection of a given food item was determined by Ivlev’s electivity index. From the results, A. spilauchen fed equally on the mosquito and chironomid larvae (χ2 = 0.8, P > 0.05). The closeness of Ivlev’s electivity index value to 0 for both chironomids and mosquito larvae further reinforces that A. spilauchen selects its prey largely on random basis than choice or preference. However, the percentage composition of mosquito larvae in the stomachs of juvenile killifish was higher than chironomid larvae. The feeding habits of this fish offer an opportunity to further explore it for the purpose of mosquito biocontrol.

Resistance to polycyclic aromatic hydrocarbon toxicity and associated bioenergetic consequences in a population of Fundulus heteroclitus.

Several locations in the Elizabeth River, VA, USA are highly contaminated with polycyclic aromatic hydrocarbons (PAHs) due to the release of creosote mixtures from wood treatment facilities. Interestingly, some populations of Atlantic killifish (Fundulus heteroclitus) inhabiting the Elizabeth River (ER) are resistant to PAH-induced teratogenesis. However, evolutionary resistance to PAHs due to chronic PAH exposure is associated with reduced fitness and increased susceptibility to other environmental stressors in at least one PAH-resistant ER killifish population. More specifically, wild-caught and first generation PAH-resistant juvenile killifish have altered metabolic demands when compared to non-resistant fish. Herein, we investigated this association further by examining a previously under-studied population captured from the creosote-contaminated site Republic Creosoting (Rep). We assessed PAH toxicity and effects on energy metabolism in Rep killifish in comparison with killifish from the reference site Kings Creek (KC). Following exposures to simple and complex PAH mixtures, Rep killifish exhibited several phenotypes associated with PAH resistance including decreased incidences of developmental cardiovascular deformities and recalcitrant cytochrome P450 1A (CYP1A) activity. We evaluated bioenergetics in killifish embryos throughout development and found elevated basal oxygen consumption rates in Rep embryos relative to KC embryos. Furthermore, juvenile F1 Rep fish had significantly lower maximal metabolic rates and aerobic scopes than KC juveniles. These results suggest that populations of killifish that have adapted or evolved to withstand the toxicity associated with PAHs consequently have altered energetic metabolism or demands. Such consequences could result in an enhanced vulnerability to other environmental and anthropogenic stressors in PAH-resistant killifish.

Experimental evaluation of predation as a facilitator of invasion success in a stream fish

Predator-prey relationships in poikilotherms are often size dependent, such as when adults of two interacting species are capable of eating juveniles of the other species. Such bi-directional predation can be important during the establishment and spread of an invading species, but its role remains poorly understood. Using a combination of laboratory and mesocosm experiments and field introductions, we demonstrate that guppies, Poecilia reticulata, prey on juvenile killifish, Rivulus hartii, and thereby facilitate their establishment in the habitat of a potential predator. Laboratory studies found that mature guppies can consume larval Rivulus, and experimental stream studies showed that guppies reduced the number of Rivulus surviving from eggs. Growth trials found that interspecific competition, while significant, cannot account for the declines in the survival of juvenile Rivulus seen in field surveys. Finally, a field experiment, in which guppies were introduced into previously guppy-free stream reaches, resulted in a marked reduction in the abundance of juvenile Rivulus relative to guppy-free controls. Together, these results indicate that reducing the native Rivulus population represents an important.mechanism promoting guppy invasion success.

The use of annual killifish in the biocontrol of the aquatic stages of mosquitoes in temporary bodies of fresh water; a potential new tool in vector control

BackgroundMosquitoes that breed in temporary pools in remote areas that dry up seasonally are especially difficult to control through chemical or biological means. The annual killifish has been suggested as a means of eradicating the aquatic stages of mosquitoes in transient pools because they can maintain permanent populations in such habitats by undergoing suspended animation or diapause during the embryonic stages to survive periodic drought. However, very little is known about the predatory activity of annual killifish and their usefulness in mosquito control.ResultsThe annual killifish, Nothobranchius guentheri, native to Tanzania, was used in this investigation. Food preference was tested under laboratory conditions by feeding juvenile killifish with 2nd instar mosquito larvae of Culex quinquefasciatus in the presence of alternative food sources, such as rotifers and chironomid larvae. Semi-field tests were conducted by introduction of hibernating killifish embryos and juvenile fish to artificial ponds in an outdoor open environment that allowed natural oviposition of Cx. quinquefasciatus. Food preference studies show that N. guentheri preferred to prey on mosquito larvae than either chironomid or rotifers. When hibernating killifish embryos were added to ponds simultaneously with the addition of freshwater, the embryos hatched and fed on mosquito larval population resulting in complete elimination of the immature stages. The introduction of juvenile fish to ponds with high density of mosquito larvae resulted in total eradication of the mosquito population due to predation by fish. Complete biocontrol of the mosquito larval population was achieved in the presence of 3 fish per m2 of pond surface area.ConclusionsThe annual killifish provides yet another tool that may be employed in the eradication diseases carried by mosquitoes through vector control, particularly in temporary bodies of freshwater. The fish can be conveniently transported in the absence of water in the form of hibernating embryos. Once introduced either as embryos or juveniles in ponds, the annual killifish can effectively reduce the larval population because of its aggressive predatory activity.

Size-dependent interactions in salt marsh fish (Fundulus heteroclitus Linnaeus) and shrimp (Palaemonetes pugio Holthuis)

Competition and predation are major biotic interactions that influence the structure of aquatic communities . The relative importance of each type of interaction is usually a function of the relative size of the organisms involved. This study used field experiments to assess potential size-dependent interactions among small juvenile killifish ( Fundulus heteroclitus ) and grass shrimp ( Palaemonetes pugio ) and larger adult killifish. Density, species combinations, and predation risk were manipulated within field enclosures on an intertidal salt marsh on Sapelo Island, Georgia. Intraspecific and interspecific competitive effects between small juveniles (larval killifish and postlarval grass shrimp) were examined in the absence and presence of predators (larger adult killifish) to determine interactions and modifications of interactions due to predators. In the absence of predators both negative intraspecific and interspecific effects occurred in the form of reduced growth of juvenile grass shrimp. Survival of juvenile shrimp was the same in the presence or absence of juvenile killifish. However, when larger adult killifish were present, the interspecific competitive effect of reduced growth in juvenile grass shrimp was not significantly different from controls. Growth and survival of juvenile fish were unaffected by increased density of conspecific juveniles and the presence of juvenile grass shrimp and adult fish predators. These results provide field evidence for interspecific competitive interactions between juveniles of two of the most abundant species of nekton utilizing salt marsh habitat along the eastern coast of North America. However, when larger adult killifish predators were present these interspecific competitive effects among similar sized juvenile killifish and grass shrimp disappeared.

Acute toxicity of cadmium, copper, zinc, ammonia, 3,3′-dichlorobenzidine, 2,6-dichloro-4-nitroaniline, methylene chloride, and 2,4,6-trichlorophenol to juvenile grass shrimp and killifish

The acute toxicity of several compounds was investigated while performing a toxicity evaluation of a complex chemical effluent. The tests were conducted for one or more of the following reasons: (1) data were not available for the chemical; (2) data were not available for the species; or (3) data were not available for the juvenile life stage of the species. Forty-eight hour acute toxicity tests were run on juvenile grass shrimp (Palaemonetes pugio) and juvenile killifish (Fundulus heteroclitus) exposed to the following compounds: cadmium, copper, zinc, ammonia, 3,3{prime}-dichlorobenzidine, 2,6-dichloro-4-nitroaniline, methylene chloride (dichloromethane) and 2,4,6-trichlorophenol.

Evaluation of Flow-Through, Static, and Recirculating Systems for the Intensive Culture of the Gulf Killifish Fundulus grandis with Observations on a Solar-Heated Recirculating System for the Bait Industry

Three systems (flow-through, static, and recirculating) for intensive culture of the Gulf killifish (Fundulus grandis) for bait were evaluated. The outdoor recirculating system proved most successful. Killifish maintained in this system attained an average weight of over 2.0 gm in 42 days, an acceptable market size. Whereas the solar-heated recirculating system sustained fish densities equivalent to l,000,000/ha and a survival rate of 86%, growth of killifish in this system was less than that observed in both the static and outdoor recirculating systems. Algae appeared to be an important nutntional component of the diet of juvenile killifish. Individuals of F. grandis fed diets supplemented with algae grew better than those maintained without them. INTRODUCTION The Gulf killifish Fundulus grandis Baird and Girard, is used extensively as a live bait along the northern Gulf of Mexico and supports a growing bait -industry (McIlwain 1977,TatumandHelton 1977, Tatumet al. 1978). However, supply of killifish-bait rarely meets the demand, especially during fall when the need is greatest (McIlwain 1977, Tatum et al. 1978). To fill this need, several attempts have been made to propagate killifish. Although the current and predominant method of rearing F. grandis is in earthen ponds (see Tatum et al. 1978), McIlwain (1977), based on limited experiments, suggested the feasibility of recirculating systems for killifish culture. Closed recirculating systems, in addition to providing some control over environmental parameters such as temperature, salinity, dissolved oxygen, and pH, require less space and aid in eliminating certain debilitating parasitic infections of killifish (see Solangi and Overstreet 1980, Solangi and Ogle 198 1). This paper reports results of several experiments on killifish culture in closed systems with preliminary observations on a solar-heated recirculating system that shows promise for the bait-fish industry. MATERIALS AND METHODS Laboratory-reared Fundulus grandis were obtained by stripping gravid male and female killifish collected from Halstead Bayou, Ocean Springs, Mississippi. Prior to experimentation, parasite-free fish were maintained in 60-1 aquaria in Instant Ocean@ at 25 loo salinity and 24 ? 2°C temperature, and were fed daily ad libitum a ration of TetraMarin' Experiments were conducted to compare Manuscript received June 23,1981;accepted May 25, 1982. flow-through, static, and recirculating systems for killifish culture and determine the 'effects of various diets on growth of F. grandis. Unless otherwise noted, tests were conducted in duplicate, and experimental fish were fed ad libitum a ration o f Bama@ Minnow Chow. Growth was calculated by differences in weight tained, and statistical analyses on growth data were conducted using procedures of Campbell (1967).

POND STUDIES ON GULF KILLIFISH (Fundulus grandis) MARICULTURE

AbstractInvestigations concerning spawning, hatching, and grow‐out of gulf killifish (Fundulus grandis) were conducted in 0.08‐ha, brackish‐water ponds at Alabama's Claude Peteet Mariculture Center during 1979. Adult gulf killifish stocked at 88,750 fish/ha and a 1:1 sex ratio in 3 spawning ponds deposited 499,777 eggs on 1,001 Spanish moss mats placed around pond margins between 1 March and 13 August. Rate of egg deposition was highest in March (4,103 eggs/day/pond) and lowest in July and August (36 eggs/day/pond). A total of 293,467 eggs and 416 mats transferred to 3 hatching ponds between 13 March and 8 May produced 219,921 juvenile killifish (75% survival) averaging 0.5 g at harvest on 6 June. Production and feed conversion in hatching ponds averaged 413.90 kg/ha and 1.9, respectively. Stocked on 6 June in 4 grow‐out ponds each at either 250,000 or 370,000 fish/ha and fed either 2 or 3 times daily, the juvenile gulf killifish reached marketable size (2.4 g and 57 mm total length) in 49 days. Production in grow‐out ponds averaged 658 kg/ha with 93% survival and 2.4 feed conversion. Analysis (2 × 2 factorial) of grow‐out data indicated no significant differences for effects of densities and feeding on mean weights of fish at harvest.

Chlorinated cooling waters in the marine environment: Development of effluent guidelines

The effects of free chlorine and chloramine on stage I lobster larvae and juvenile killifish were investigated in continuous flow bioassay units. In comparing mortality and changes in standard respiration rates during and after exposure to either chlorine form, significant respiratory stress was observed with exposure to sublethal levels. Sublethal responses to free and combined chlorine should be considered when establishing regulations for chlorine residuals in cooling waters.

The effect of detritus and ration size on the growth of Fundulus heteroclitus (L.)

In a laboratory experiment using juvenile killifish, Fundulus heteroclitus L., detritus addition to a commercial fish food diet of 0, 2, 4, 6, 7, 10 and 14 % dry body weight/day did not significantly affect the growth of Fundulus when compared with replicate groups not receiving detritus. Even though Fundulus ingested detritus, they did not apparently use it for maintenance or growth. The fish required at least a daily ration of commercial fish food of 4–6 % dry body weight for maintenance. The ash content of fish fed at diets of fish food below 4 % dry weight/day increased, and the C N ratio decreased, indicating the inadequacy of these rations. Fish grew almost at field rates at higher amounts of commercial fish food. When feeding in the field, fish at above-maintenance rations must exert a strong influence on prey populations.

The effects of complete darkness and vitamin C supplement on the killifish, Fundulus heteroclitus, adapted to sea water. I. Calcium metabolism and gonadal maturation.

AbstractAdaptation to complete darkness for eight months had no effect on calcium metabolism in adult male Fundulus heteroclitus in sea water. However, scoliosis and hypocalcemia were evident in juvenile killifish kept in complete darkness for six and a half months. Hypocalcemia was also seen in juveniles after three and a half months in complete darkness but this fall in serum calcium level was prevented by vitamin C supplement in the diet. Complete darkness also induced a delay in testicular maturation in both adults and juveniles but this defect was not corrected by vitamin C supplement.