Salinity tolerance of the guppy, Poecilia reticulata Peters

Experiments were conducted to determine the adaptability of the guppy to various salt concentrations. The guppy, Poecilia reticulata , (total length 11–40 mm) were subjected to abrupt and gradual changes from fresh water (salinity=0.1%) to various salinities (%). No mortality occurred when the fish were transferred from fresh water to 50% sea water (19.5%). Through gradual adaptation from 50% sea water to 80% of the fish were able to tolerate 100% (39%) sea water for 7 days. After a 7 day stay in sea water, fish were readapted to fresh water during a 3 h period. Through gradual adaptation fish were also able to tolerate salinities ranging from 39.0% (100% sea water) to 58.5%. After a 30 day stay in 150% sea water (58.5%), fish were readapted to fresh water over a 5 h period. The results indicate that they were well able to tolerate the abrupt change from 100 or 150% sea water to fresh water. Females that stayed in 150% sea water (58.5%) for 30 days had embryos in their gonads.     

Myopathy and steatitis in the common guppy, Poecilia (Lebistes) reticulata (Peters)

There was 1% mortality among female guppies just imported from Southeast Asia. Moribund fish showed discoloration, lethargy and kyphosis. Microscopically, myopathy and steatitis were observed, together with an extensive ceroid storage. These findings are indicative of vitamin E deficiency, and illustrate the risk of using fish of unknown origin in toxicological studies.     

Influence of water-borne iron on the liver of Poecilia reticulata (Peters 1859)

The influence of water-borne iron (500 μg × 1^-1 and 2 mg × 1^-1) on the liver of Poecilia reticulata is studied by means of electron microscopy. The uptake and effect of iron is affected by a. the chemical speciation of the metal: Iron complexed with tri-polyphosphates is more deleterious than inorganic Fe³⁺; b. the nutritional status of the fish: In food-deprived Poecilia reticulata iron is absorbed and enhances starvation-induced liver damage. In fed animals, there is no uptake at all. Mild alterations of hepatocyte ultrastructure are attributed to an unspecific stress response.     

Recognition of chemical stimuli by guppy, Poecilia reticulata Peters

An alimentary conditioned reflex to beta-phenylethanol and a subsequent differentiation of cumarine were elaborated in conditions of simultaneous paired choice in guppies. It was shown that beta-phenylethanol in a concentration not over 7 X 10(-6) M is perceived through olfaction. The conditioned reflex persists for a long time: twenty five to fifty days after section of the olfactory nerves (the conditioned reflex is restored after their regeneration) and at least seventy days in intact fishes.     

The effects of population density on fecundity and fertility in the guppy, Poecilia reticulata (Peters)

Experiments were performed to examine the influence of population density on the fecundity and fertility in the guppy, Poecilia reticulata . The frequency of females with only ova or with different combinations of reproductive units and developmental stages in the ovary was significantly different between different densities but not between females with one and two gestations from the same population density. The ovarian width of females with one gestation from the lowest density was significantly larger than in the highest population density. Gonad length and height and ovarian volume of females with two gestation periods were larger in the lowest compared with the highest density. After one gestation, females at the lowest population level had greater ovarian length, height, gonad weight, width and volume compared with those from the higher density. Ovarian length, height and volume and gonad weight were also significantly greater among females of two gestation periods in the lowest than in the second lowest density. The average gonadosomatic ratio was highest in the lowest population density. A significant correlation was found between gonad volume and total body weight and between gonad volume and ovarian weight of females at every population level. This was also the case when ovarian weight vs. total body weight was examined in each population density. Only at the lowest population level was there a significant correlation between fecundity and total body length and between fertility and body length. A significant relationship was also found between gonad volume and total body length and between gonad weight and body length at the same population level. No significant difference of fecundity and ovum size was found between females of one and two gestation periods from the same density. Fecundity and fertility were significantly higher among females of one and two gestation periods from the lowest than from the highest density.     

Modification of the response to high density conditions in the guppy, Poecilia reticulata (Peters)

An examination was made of some of the factors which influence the response to density in the guppy. Water from high density fish was given to fish populations kept at high and low densities. This induced high density behaviour in low density fish by increasing aggression and decreasing courtship. But giving 'fresh' water to high density fish failed to alleviate the response to density. 'High density water' slightly reduced the numbers of young found in low density groups. High density fish kept in the dark had more young than high density groups in the light; and the number of young found was decreased when 'high density water' was given to low density fish. The number of ovarian stages was decreased in the dark in high density and was not overridden by the type of water. Giving 'high density water' to low density fish decreased the number of oocytes stage III, but the interaction between water and 'light' was confounded by the total numbers of ovarian stages. Increasing the 'visual space' of high density fish with mirrors partially decreased aggression and increased courtship and number of young found; but had little affect upon the number of ovarian stages. Decreasing the number of physical contacts by keeping the fish chronically tranquillized reduced the activity of the fish. This reduced the aggression of the high density fish and also reduced the differences between the high and low density fish on the basis of their courtship scores, number of young found and number of stages in the ovary. Fish from differing population sizes were given a choice between varying fish densities. The fish from a 'normal' sized population and with an extended visual field, tended to make a choice conforming to the overall selections compared with fish from populations of extreme size and with a reduced visual field.     

Effect of light intensity on the shoaling behaviour of the guppy (Poecilia reticulata)

It has been shown that the tendency of fish to shoal decreases as night falls. Much is known about shoaling in the daytime, however, little is known about the social behaviour of fish at night. Although the nocturnal disintegration of shoal structure is the conventional expectation for most diurnal marine fish, it has not yet been investigated for diurnal freshwater fish. This possibility has been investigated using guppies (Poecilia reticulata), collected from the wild, as an experimental model. Three preference tanks were used, one of which permitted only visual cues, another only olfactory cues and the other both visual and olfactory cues. Shoaling tendency was observed at four different light intensities (8 wt/m, 0·05 wt/m, 0·025 wt/m, 0·003 wt/m). These light intensities were chosen to mimic daylight, dawn/dusk, clear night and cloudy night conditions, respectively. Trials were carried out on randomly selected male guppies. Results indicated that with both modalities present fish significantly preferred the stimulus shoal at all light intensities. However with only one modality to indicate the presence of the shoal, fish showed no significant shoaling tendency at any of the diminished light intensities. A test of shoal cohesion at the four different light intensities was carried out on freely interacting fish. This test condition was chosen to mimic the situation of guppies in the wild. The results to date suggest that guppies continue to shoal during dusk (at low light intensities) but not during the night. These findings make an important contribution to our understanding of the social behaviour of fish at night and deserve further investigation.     

Aquatic surface respiration,an adaptive response to hypoxia in the guppy,Poecilia reticulata (Pisces,Poeciliidae)

Synopsis Aquatic respiration at the air-water interface, herein termed aquatic surface respiration (ASR), is used by the guppy,Poecilia reticulata (Poeciliidae) to meet oxygen demand in hypoxid water. A specific position in which the head contacts the surface and the jaws open just beneath the surface is adopted. ASR is initiated at a P0₂ of about 50 torr and the percent time spent rises in a steep, linear fashion as PO₂ decreases. Below 4 torr more than 90% of the animal's time is spent in ASR. Males spend less time in ASR than do females. The percent time in ASR increases with increasing size of female guppies, but decreases with increasing size of male guppies. At low oxygen (18 torr) laboratory-born guppies derived from stocks likely to experience deoxygenation spend less time in ASR than do guppies derived from stocks less likely to experience deoxygenation. The percent time in ASR increases with temperature when PO₂ is held constant. Acclimation to low oxygen decreases the percent time in ASR.Guppies not permitted ASR die in 6–41 h at 14–17 torr and 10–15 min at 1–4 torr. Guppies performing ASR survive the duration of experiments at 13–35 torr (13 days), 14–17 torr (96 h), and 1–4 torr (9.5 h). Activity, courtship, and dive duration in response to a shadow stimulus are all reduced by low oxygen. ASR is an effective alternative to aerial respiration as an adaptation to hypoxic waters, but is probably energetically and temporally more costly.     

Marked variation in parasite resistance between two wild populations of the Trinidadian guppy, Poecilia reticulata (Pisces: Poeciliidae)

This is the first study to demonstrate significant differences between two natural Trinidadian guppy populations in susceptibility to a pathogenic monogenean parasite, Gyrodactylus turnbulli . Following experimental infection with an isogenic laboratory culture of G. turnbulli , fish from the Upper Aripo (UA) lost parasites more slowly and carried up to three times as many parasites at peak infection than did those from the Lower Aripo (LA). The UA population appeared to be more susceptible than the LA fish, even though fish of both populations were naïve to this particular laboratory strain of G. turnbulli and had not encountered any gyrodactylid infection for at least 65 days. The parasite infection reduced the feeding response and feeding activity of UA and LA fish to a similar extent. Our findings suggest that this ectoparasite may have an important impact on the evolutionary biology of guppies (and possibly of other teleosts), particularly as the prevalence of Gyrodactylus infection in natural populations may be as high as 50%. We discuss the role of parasite infections on natural and sexual selection, the good genes model and the implications for immunogenetics in small genetically isolated host populations.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 645–651.     

The effects of three different dietary protein levels on the fecundity in the guppy, Poecilia reticulata (Peters)

Experiments were performed to investigate the influences of dietary protein on fecundity in the guppy, Poecilia reticulata . No significant differences in total body length and standard length were found between females given food with different protein levels. A significantly higher total body weight was found both in females fed on 47% and 31% protein compared with females given 15% protein. The frequencies of females with only intrafollicular embryos or with only ova or both embryos and ova in the ovary were not significantly different between populations given different protein amounts. There was a significantly lower frequency of females without embryos and ova but with previtellogenic oocytes in the group given highest protein (47%) compared with the group fed on 31%. Significantly higher values of ovarian length, width and gonad weight were found among females given 47% protein compared with females fed on 15% protein. The ovarian height was significantly higher only in females given the highest protein amount when compared with the group fed on 31% protein. No significant difference of ovarian volume was found between groups given different protein contents. The average gonadosomatic ratio was highest in the groups fed on 47% protein. Significant correlations were found between gonad weight and total body weight of females in each group. Ovarian volume versus total body weight as well as versus gonad weight also yielded significant correlations in all groups. No significant differences of fecundity were found either between females given 47% and 31% protein or between females fed on 47% and 15% protein. A somewhat higher number of ova per individual fish was, however, observed among females given 31% when compared with females fed on 15% protein. The ovum size remained the same between groups given different protein contents. No significant correlation was found between fecundity and ovum diameter in the groups.     

Joint action toxicity of spent lubrication oil and laundry detergent against Poecilia reticulata (Telostei: Poeciliidae)

Single and joint action bioassays using spent lubrication oil, laundry detergent and a mixture of both (based on a 1:1 ratio of their 96h LC₅₀ values) against the guppy Poecilia reticulata were carried out. On the basis of 96h mortality data, laundry detergent (LC₅₀ value - 0.033g l^?1) was found to be approximately 1 147 times more toxic than spent lubrication oil (96hrs LC₅₀ — 37.72g l^?1) when acting singly against P. reticulata. Joint action bioassays revealed a synergistic effect, with the mixture of the two test compounds being about 12 000 and 10 times more toxic, respectively, than either spent lubrication oil or laundry detergent acting singly. The significance of these results should affect both local and national waste disposal management policies.     

Testing the interactive effects of carotenoids and polyunsaturated fatty acids on ejaculate traits in the guppy Poecilia reticulata (Pisces: Poeciliidae)

Using the polyandrous livebearing guppy Poecilia reticulata, this study revealed no main effects of carotenoids in the diet on ejaculate traits, but significant main effects of polyunsaturated fatty acids (PUFAs) on sperm viability and weak but significant interacting effects of both nutrients on sperm length. Collectively, these findings not only add evidence that PUFAs are critical determinants of sperm quality, but also provide tentative evidence that for some traits these effects may be moderated by carotenoid intake.     

Ultraviolet vision and mate choice in the guppy (Poecilia reticulata)

Ultraviolet (UV) vision is well documented for many speciesof vertebrates. UV cues are known to be used in foraging, navigationand in mate choice. We conducted a series of behavioral experimentsto investigate the role of UV perception in mate choice inboth female and male guppies (Poecilia reticulata). In ourexperiments the visual appearance of potential mates was manipulatedusing either UV transmitting (UV+) or UV blocking (UV-) filters.Female guppies significantly preferred UV+ males. Male guppiestended to prefer UV- females, but their preferences were marginallynonsignificant. Further experiments investigating the roleof luminance, indicate that UV wavelengths are probably beingused for color discrimination rather than for detecting differencesin brightness. These experiments raise the possibility thatUV is used in mate assessment in different ways by male andfemale guppies. This may reflect the different strategies thatthe two sexes have in order to maximize reproductive success.To our knowledge, these are the first data showing that UVis used by any fish species in mate selection.