Ipsilateral retinal projections into the tectum during regeneration of the optic nerve in the cichlid fish Haplochromis burtoni: a Dil study in fixed tissue.

Retinal projections were experimentally manipulated in a bony fish to reveal conditions under which considerably enlarged ipsilateral projections developed and persisted. Three experimental groups were studied: animals after unilateral enucleation, after unilateral nerve crush, and after enucleation and crush of the remaining optic nerve. At 29 days after unilateral enucleation alone, no enhanced ipsilateral projection had developed. After nerve crush, however, large numbers of retinal fibers regenerated into the ipsilateral tectum. Retrogradely filled, ipsilaterally projecting ganglion cells were distributed throughout the entire retina. After 15 days regenerating retinal fibers covered the entire ipsilateral tectum. At later stages the ipsilateral projection showed progressive reduction in coverage of the tectum. Combining enucleation with nerve crush led to an ipsilateral projection that covered the tectum at 28 days and later. In this experimental situation the development of an ipsilateral projection appears to be a two-step process: (1) Fibers are rerouted to the ipsilateral side at the diencephalon, and (2) ipsilateral fibers persist in the tectum only in the absence of a contralateral projection while they appear to be eliminated in the other cases.     

Ipsilateral retinal projections into the tectum during regeneration of the optic nerve in the cichlid fish Haplochromis burtoni: A dil study in fixed tissue

Retinal projections were experimentally manipulated in a bony fish to reveal conditions under which considerably enlarged ipsilateral projections developed and persisted. Three experimental groups were studied: animals after unilateral enucleation, after unilateral nerve crush, and after enucleation and crush of the remaining optic nerve. At 29 days after unilateral enucleation alone, no enhanced ipsilateral projection had developed. After nerve crush, however, large numbers of retinal fibers regenerated into the ipsilateral tectum. Retrogradely filled, ipsilaterally projecting ganglion cells were distributed throughout the entire retina. After 15 days regenerating retinal fibers covered the entire ipsilateral tectum. At later stages the ipsilateral projection showed progressive reduction in coverage of the tectum. Combining enucleation with nerve crush led to an ipsilateral projection that covered the tectum at 28 days and later. In this experimental situation the development of an ipsilateral projection appears to be a two-step process: (1) Fibers are rerouted to the ipsilateral side at the diencephalon, and (2) ipsilateral fibers persist in the tectum only in the absence of a contralateral projection while they appear to be eliminated in the other cases. © 1992 John Wiley & Sons, Inc.     

Spectral sensitivity of the African cichlid fish,Haplochromis burtoni

Summary Spectral sensitivity of the cichlid fishHaplochromis burtoni was measured under both scotopic and photopic conditions using a two-choice, food reward, operant conditioning paradigm. The highest absolute sensitivity (scotopic) is one quantum for every 5 to 50 rods measured at 475 nm (equivalent to a corneal irradiance of 3.8×10⁶ Q s^–1 cm^–2). A P500₁ photopigment apparently mediates spectral sensitivity over most of the visible spectrum; microspectrophotometric studies of rods had previously shown them to contain this photopigment. However, the scotopic behavioral action spectrum shows a sensitivity to short wavelength light higher than is consistent with a P500₁ photopigment alone mediating the scotopic visual process. Determinations made under photopic conditions reveal a behavioral action spectrum broader than that found under scotopic conditions and consistent with mediation by interaction of the three known cone types in an opponent processing manner. The calculated photopic threshold value of approximately 10⁴ Q s^–1 (receptor)^–1 is in agreement with results from other species and corresponds to a corneal irradiance of about 7×10¹⁰Q s^–1cm^–2.     

Light-induced modulation of retinal development in the cichlid fish Haplochromis sauvagei (PfefFer, 1896)

Phenotypic modulation is a common feature in haplochromine cichlids. External changes influence the phenotype within the limits set by the genetic program. Retinal development in the cichlid Haplochromis sauvagei has been observed in specimens reared in various chromatic environments and in darkness. Rearing in darkness led to the reduction of photoreceptor densities, the apparent loss of single cones and the enlargement of double cones. To a lesser degree, similar effects were observed in specimens deprived from short-wave light. Ganglion cell densities were not affected by light deprivation. The light-induced alterations could be the result of changes in developmental rates within the retina or of early degeneration. The modulation seems to cause a reduction of blue sensitivity, possibly for the benefit of luminosity or long-wavelength detection. This would agree with the combination of decreased light intensity and a spectral shift towards the longer wavelengths as is the case in the natural environment of the Lake Victorian haplochromines. In that sense, the modulation is probably adaptive.     

The function of anal fin egg-spots in the cichlid fish Astatotilapia burtoni

Color and pigmentation patterns of animals are often targets of sexual selection because of their role in communication. Although conspicuous male traits are typically implicated with intersexual selection, there are examples where sex-specific displays play a role in an intrasexual context, e.g. when they serve as signals for aggression level and/or status. Here, we focus on the function of a conspicuous male ornament in the most species-rich tribe of cichlid fishes, the haplochromines. A characteristic feature of these ca. 1500 species are so-called egg-spots in form of ovoid markings on the anal fins of males, which are made up of carotenoid based pigment cells. It has long been assumed that these yellow, orange or reddish egg-spots play an important role in the courtship and spawning behavior of these maternal mouth-brooding fishes by mimicking the eggs of a conspecific female. The exact function of egg-spots remains unknown, however, and there are several hypotheses about their mode of action. To uncover the function of this cichlid-specific male ornament, we used female mate choice experiments and a male aggression test in the haplochromine species Astatotilapia burtoni. We manipulated the number and arrangement of egg-spots on the anal fins of males, or removed them entirely, and tested (1) female preference with visual contact only using egg-traps, (2) female preference with free contact using paternity testing with microsatellites and (3) male aggression. We found that females did not prefer males with many egg-spots over males with fewer egg-spots and that females tended to prefer males without egg-spots over males with egg-spots. Importantly, males without egg-spots sired clutches with the same fertilization rate as males with egg-spots. In male aggression trials, however, males with fewer egg-spots received significantly more attacks, suggesting that egg-spots are an important signal in intrasexual communication.     

The development of the ipsilateral retinothalamic projections in the Xenopus toad.

The appearance of ipsilateral terminal degeneration in the thalamic visual centers is studied with the aid of the Fink-Heimer II technique in Xenopus larvae and postmetamorphic toadlets following unilateral eye removal. The youngest age at which degeneration can reliably be shown in the lateral geniculate complex (nucleus of Bellonci and corpus geniculatum thalami) was at stage 62, that is, 10-12 days before metamorphic climax. The whole compliment of the ipsilateral retinothalamic projection develops only in postmetamorphic toadlets, and it is much more abundant in Xenopus than in Rana species. The first appearance of the ipsilateral degeneration in the lateral geniculate complex coincides in time with the first ipsilateral visuotectal responses described by others. The possibility that the two phenomena may have a closer relationship than the mere time coincidence, is discussed.     

Heritability and adaptive significance of the number of egg-dummies in the cichlid fish Astatotilapia burtoni

Cichlid fishes are a textbook example of rapid speciation and exuberant diversity--this applies especially to haplochromines, a lineage with approximately 1800 species. Haplochromine males uniquely possess oval, bright spots on their anal fin, called 'egg-spots' or 'egg-dummies'. These are presumed to be an evolutionary key innovation that contributed to the tribe's evolutionary success. Egg-spots have been proposed to mimic the ova of the mouthbrooding females of the corresponding species, contribute to fertilization success and even facilitate species recognition. Interestingly, egg-spot number varies extensively not only between species, but also within some populations. This high degree of intraspecific variation may appear to be counterintuitive since selection might be expected to act to stabilize traits that are correlated with fitness measures. We addressed this 'paradox' experimentally, and found that in the haplochromine cichlid Astatotilapia burtoni, the number of egg-spots was related to male age, body condition and dominance status. Intriguingly, the egg-spot number also had a high heritable component (narrow sense heritability of 0.5). These results suggest that the function of egg-spots might have less to do with fertilization success or species recognition, but rather relate to mate choice and/or male-male competition, helping to explain the high variability in this important trait.     

Maternal care and altered social phenotype in a recently collected stock of Astatotilapia burtoni cichlid fish

For over 30 years, the African cichlid fish, Astatotilapia burtoni, has been an important model system for studying the mechanisms underlying socially mediated behavioral change, with the focus being the dominance behavior of males. A recently collected wild-stock (WS) of this species invigorates interest in parallel studies of females' behavior. Here, we describe a robust 'good-mother' phenotype, increased maternal affiliation in fry, and subtle differences in males' behavior that are exhibited by this new stock. While the females of both the laboratory-stock (LS) and the WS brood the developing fry in their buccal cavity, only the WS continues to provide maternal care after initial release of the fry while the LS engage in filial cannibalism. We show that weight loss during starvation, either during brooding or with restriction of food, is greater in the LS than in the WS; thus, the observed behavioral differences may be tied to metabolic differences. The WS also exhibits a robust androgen response to challenge during the maternal care phase. Given the increasing power of genomic tools available for this species, the comparison of these two stocks will offer the opportunity to investigate the genetic and genomic basis of behavioral differences.     

Social regulation of the electrical properties of gonadotropin-releasing hormone neurons in a cichlid fish (Astatotilapia burtoni)

Variation in reproductive capacity is common across the lives of all animals. In vertebrates, hypothalamic neurons that secrete GnRH are a primary mediator of such reproductive plasticity. Since social interactions suppress gonadal maturity in the African cichlid fish, Astatotilapia (Haplochromis) burtoni, we investigated whether the electrical properties of GnRH neurons were also socially regulated. Adult A. burtoni males are either territorial (T) and reproductively active or nonterritorial (NT) and reproductively regressed, depending upon their social environment. We compared the basic electrical properties of hypothalamic GnRH neurons from T and NT males using whole-cell electrophysiology in vitro. GnRH neurons were spontaneously active and exhibited several different activity patterns. A small fraction of neurons exhibited episodic activity patterns, which have been described in GnRH neurons from mammals. The type of activity pattern and spontaneous firing rate did not vary with reproductive capacity; however, several basic electrical properties were different. Neurons from T males were larger than those from NT males and had higher membrane capacitance and lower input resistance. In neurons from NT males, action potential duration was significantly longer and after-hyperpolarization characteristics were diminished, which led to a tendency for neurons from NT males to fire less rapidly in response to current injection. We predict this could serve to decrease GnRH release in NT males. These data are the first electrophysiological characterization of hypothalamic GnRH neurons in a nonmammalian species and provide evidence for several changes in electrical properties with reproductive state.     

Hypertrophy of gonadotropin releasing hormone-containing neurons after castration in the teleost, Haplochromis burtoni.

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci in the cichlid fish in Lake Victoria, Haplochromis chilotes

Twelve short tandem repeat markers were successfully isolated from a cichlid, Haplochromis chilotes, in Lake Victoria, and characterized in Haplochromis pyrrhocephalus. The microsatellite regions of these markers were found to have between two and 48 alleles with heterozygosity ranging from 0.07 to 0.97. No loci showed significant departures from the Hardy–Weinberg or linkage equilibrium after the Bonferroni correction (P > 0.05). Cross‐species amplification in other cichlids of Lake Victoria, Haplochromis laparogramma, Lithochromis rubripinnis, L. rufus and Haplochromis sp. ‘rockkribensis’, was successful.     

The Ontogeny of Social Behavior and Body Coloration in the African Cichlid Fish Haplochromis burtoni

The ontogeny of behavioral patterns and body coloration are described for the African cichlid fish, Haplochromis burtoni. The development of particular color patterns correlates directly with appearance of behavioral patterns which “use” those color patterns. There is a flexible timetable associated with these events which depends on both social and environmental factors.     

GnRH-systems in the forebrain of cichlid fish.

The neuronal systems that contain gonadotropin-releasing hormone (GnRH) were quantitatively examined in the forebrain of two cichlid species (Oreochromis niloticus Lin. and Tilapia maria Boulenger) using tracing methods and immunostaining. In both species the nucleus olfacto-retinalis and a population of neurons in the basal preoptic region contained GnRH. The nucleus olfacto-retinalis was divided into several neuronal subpopulations which differed with respect to cytology, projection pattern, and peptide content. GnRH cell number increased with body size, the rates being different for the different subpopulations. A sexual dimorphism was found in the basal preoptic region of Tilapia; males had significantly fewer GnRH-containing cells than females. Selective staining of the basal preoptic region demonstrated that this cell group is the main source of GnRH-innervation of the pituitary gland and indicate that the molecular forms of GnRH expressed in the two cell populations studied may be different.     

Testing clove oil as an anaesthetic for long-distance transport of live fish: the case of the Lake Victoria cichlid Haplochromis obliquidens

Clove oil can be used as an anaesthetic in the handling of marine and freshwater fish. Few studies report on its use for periods up to 48 h, for example, under long‐distance transport conditions. This study tested the effect of different clove oil concentrations for 1–48 h on recovery and survival of the cichlid Haplochromis obliquidens, an ornamental fish species endemic to Lake Victoria. Haplochromis obliquidens were anaesthetized for 1 h using 5–25 μl L^?1 clove oil. There was no correlation between clove oil concentration and post‐anaesthesia recovery time (P = 0.15). On average, fish recovered within 9.5 ± 2 min, and no fish died within 24 h after recovery. Results from exposure of fish to 18–20 μl L^?1 clove oil for up to 48 h suggested a narrow margin of safety as this concentration range induced mortality. At 18 μl L^?1 recovery times ranged from 3 to 43 min between 24 and 36 h exposure, while fish exposed longer than 36 h recovered within 1–10 min, or within 1–2 min after 44–48 h. At the end of a 48‐h transport experiment total ammonia levels were higher in transport water containing anaesthetized fish than for non‐anaesthetized fish (1.65 ± 0.19 and 0.54 ± 0.08 mg L^?1 NH + NH₃, respectively). The combined use of clove oil and the selective ammonium ion exchanger zeolite was considered feasible as ammonia levels could be reduced by up to 82% compared to control bags without zeolite.     

The angular orientation of the black eye-bar in Haplochromis burtoni (Cichlidae,Pisces) and its relevance to aggressivity

Summary The effect of the black eye-bar in Haplochromis burtoni on the attack rate of conspecific males was found, using dummies, to depend on the angular orientation of this bar with respect to the body axis of the fish (Figs. 1, 4): The increment in attack rate increases as the black eye-bar parallels more closely the profile of the forehead and decreases as the bar approaches an orientation perpendicular to the forehead. This is valid independent of the actual body posture of the dummy bearing the black bar as could be shown by presenting dummies in a horizontal as well as in a head downward position. However, the head-down posture itself was found to cause an extra increment in attack rate, which may be considered to be additively or multiplicatively superimposed upon the increment determined by the orientation of the eye-bar with respect to the body axis (Fig. 4).Mit Unterstützung der Deutschen Forschungsgemeinschaft im Rahmen des SFB 50.We wish to thank Ann and John Thorson for their most stimulating discussion of the paper.     

Evidence for a driving role of ingrowing axons for the shifting of older retinal terminals in the tectum of fish.

In amphibians and teleosts, retina and tectum grow incongruently. In order to maintain the retinotopy of the retinotectal projection, Gaze, Keating, and Chung (1974) postulated a shifting of terminals throughout growth. In order to test the possibility that ingrowing retinal fibers are the driving force for this shifting, we induced a permanent retinal projection into the ipsilateral tectum in juveniles of the cichlid fish Haplochromis burtoni. The surface of the tectum had increased (11-18 months later) 2.5-5.8 times, and the surface of the retina 8.6-14 times. Filling of ganglion cells with horseradish peroxidase (HRP) retrogradely from the tectum showed ipsilaterally regenerating ganglion cells only in the center of the retina. The position of ganglion cells indicated that the ipsilateral projection derived only from axotomized and regenerating retinal ganglion cells but not from those newly born. Ipsilaterally projecting retinal fibers showed terminals only in the rostral half of the tectum. Comparison of area of terminations of ipsilaterally projecting ganglion cells at various times after the crush provided no evidence for expansion or a shift into caudal tectal areas throughout the period of growth. These findings are compatible with the idea that newly ingrowing fibers induce older terminals to move caudally.