John R. Burns

Internal fertilization, testis and sperm morphology in glandulocaudinae fishes (Teleostei: Characidae: Glandulocaudinae)

In this report, the gonads of 32 glandulocaudine species, representing 18 genera, are compared with 11 outgroup characiform species. Through the presence of spermatozoa within the ovarian cavity, internal fertilization of the female is confirmed for the 16 genera for which mature ovaries were available. No outgroup ovary studied contains spermatozoa. All mature glandulocaudine testes have a large portion of the posterior testis, which is devoid of developing germ cells and spermatocysts (aspermatogenic), devoted to sperm storage, with the degree of partitioning in that region varying greatly within the group. All outgroup species examined have spermatozoa with spherical nuclei. With the exception of the species of the genus Planaltina, which also have spherical nuclei, all glandulocaudines have elongated nuclei, which vary among the species from 3.6 μm to 31.6 μm in length. Distinct sperm packets (spermatozeugmata) are formed in five genera by two different methods. In the genera Xenurobrycon, Tyttocharax, and Scopaeocharax, all of the tribe Xenurobryconini, the spermatozeugmata are formed within the spermatocysts and released fully formed. In all genera of the tribe Glandulocaudini, which includes Glandulocauda and Mimagoniates, loose spermatozoa are released which cluster into spermatozeugmata within the posterior storage areas. These morphological specializations are discussed within a phylogenetic framework as adaptations for internal fertilization and are hypothesized to be independently derived.

Morphology and histology of the male reproductive system in two species of internally inseminating south american catfishes, trachelyopterus lucenai and T. galeatus (Teleostei: Auchenipteridae)

As part of an effort to characterize reproductive modifications in internally inseminating catfishes, ovaries and male reproductive systems were examined histologically in two species of auchenipterid catfishes, Trachelyopterus lucenai and T. galeatus, from southeastern Brazil. Internal insemination was documented in both species by the presence of sperm within ovaries. Although there is some variation in gross morphology of the male reproductive systems between the two species, both have four main regions: spermatogenic lobes, sperm storage regions, and secretory and storage regions of the seminal vesicle. In both species, the anterior portion of the reproductive system is spermatogenic and divided into numerous finger‐like lobes. Posterior to the spermatogenic area is the storage region of the seminal vesicle, a large median structure with a honeycomb‐like appearance. This region is consistently larger in T. lucenai. Attached to the storage region of the seminal vesicle in both species are secretory lobes comprised of tubules lined by secretory cells. These lobes in T. lucenai are small and located on the anterior aspect of the storage region of the seminal vesicle, whereas in T. galeatus the lobes are much larger and located laterally. The sperm storage regions of T. lucenai consist of two large lobes located ventral to the storage region of the seminal vesicle. Highly compact sperm packets (spermatozeugmata) fill the lumina of the ramifying tubules of these regions. Each spermatozeugma consists of elongate nuclei tightly arranged parallel to one another. In T. galeatus two distinct sperm storage regions are present. Just posterior to the spermatogenic lobes a series of small lobes serve as anterior sperm storage regions. Posterior to the secretory lobes of the seminal vesicle is a series of lobes, at the most posterior aspect of the reproductive tract, that serve as posterior sperm storage regions. Both are identical, histologically, to the sperm storage regions of T. lucenai. An absence of compact spermatozeugmata in the T. galeatus specimens may be related to variations in their sexual activity. The descriptions presented here allow for consistent terminology for comparison of regions of the male reproductive system based on presumed function. J. Morphol. 246:131–141, 2000

Novel Gill-Derived Gland in the Male Swordtail Characin, Corynopoma riisei (Teleostei: Characidae: Glandulocaudinae)

early stages of maturation. The gland appears to develop from the anterior 813 gill filaments of the first gill arches. The gill secondary lamellae shorten such that their only remnants in most of the mature gill gland are capillaries at the bases of the columnar cells that line the chambers. The edges of adjacent gill filaments must fuse to form the chambers that open into the gill cavity through antero-ventrally oriented apertures. Skeletal muscle and cartilage from the original gill filaments remain within the chamber walls. Degree of expansion and secretory activity of the glands varied among the 11 mature males. Based on histological characteristics of the gland, its location, and the complex courtship behavior of this species, we hypothesize that the gill gland is producing some type of female attractant (pheromone).

Insemination in Eight Species of Cheirodontine Fishes (Teleostei: Characidae: Cheirodontinae)

Internal fertilization is relatively rare in the superorder Ostariophysi (Breder and Rosen, 1966). Internal fertilization is unknown in the Gonorhynchiformes and Cypriniformes and in the Siluriformes occurs only in the Auchenipteridae and Ageneiosidae (von Ihering, 1937; Loir et al., 1989). Within the Characiformes, some species of the subfamily Glandulocaudinae, family Characidae, display internal fertilization (Roloff, 1949; Kutaygil, 1959; Weitzman and Fink, 1985), and spermatozoa are present in ovaries from all 16 genera for which mature females are available (Burns et al., 1995). At least one species of the characid genus Creagrutus is said to be internally fertilized (Breder and Rosen, 1966). Cheirodontines are a small group of approximately 60 species of freshwater fishes (subfamily Cheirodontinae, family Characidae) occurring from Central America south to Argentina (Malabarba, 1994). The purpose of this study was to determine whether insemination and in-

Sperm and Spermatozeugma Ultrastructure in the Inseminating Catfish, Trachelyopterus lucenai (Ostariophysi: Siluriformes: Auchenipteridae)

Abstract This study presents details of the ultrastructure of the spermatozeugmata and spermatozoa of the South American catfish, Trachelyopterus lucenai, an inseminating species. Spermatozoa are tightly packaged into unencapsulated bundles, spermatozeugmata, with as many as 130 cells comprising a single packet. Within an individual spermatozeugma, cells are aligned side by side such that the anterior region of the bundle is comprised of nuclei, the middle region midpieces, and the posterior region flagella. Integrity of the packet appears to be maintained by specialized junctions between adjacent cells along their entire lengths. Each spermatozoon is characterized by an elongate nucleus containing condensed chromatin and a fossa at the posterior end. The elongate midpiece contains multiple mitochondria, abundant glycogen deposits, and accessory microtubules that run along the length of the midpiece. The ultrastructural modifications of the spermatozoa are discussed as possible adaptations associated with the reproductive mode of insemination.

The Reproductive Cycle and Its Environmental Control in the Pumpkinseed, Lepomis gibbosus (Pisces: Centrarchidae)

TURNER, F. B. 1962. The demography of frogs and toads. Q. Rev. Biol. 37:303-314. VAN GELDER, J. J., AND H. C. J. OOMEN. 1970. Ecological observations on amphibia in the Netherlands. I. Rana arvalis Nilsson: reproduction, growth, migration, and population fluctuations. Neth. J. Zool. 20:238-252. VOLPE, E. P. 1953. Embryonic temperature adaptations and relationships in toads. Physiol. Zool. 26: 344-354. WAITE, E. R. 1927. The fauna of Kangaroo Island, RNER, F. B 1962. The demography of frogs and oads. Q. Rev. Biol. 37:30 -314. AN GELDER, J. J., AND H. C. J. OOMEN. 1970. South Australia. No. 3. The reptiles and amphibians. Trans. Roy. Soc. S. Aust. 51:326-329. WOODRUFF, D. S. 1972. The evolutionary significance of hybrid zones in Pseudophryne (Anura: Leptodactylidae). Unpubl. Ph.D. Thesis. Dept. of Zoology, Univ. of Melbourne.

Testis morphology and spermatozeugma formation in three genera of viviparous halfbeaks: Nomorhamphus, dermogenys, and Hemirhamphodon (Teleostei: Hemiramphidae)

The testes of 19 species of viviparous halfbeaks from three genera, Nomorhamphus, Dermogenys, and Hemirhamphodon, are examined histologically. The testes are unfused, paired organs running laterally along the body wall on either side of the gut. In all genera, primary spermatogonia are restricted to the distal termini of the testicular lobules just beneath the tunica albuginea, conforming to the typical atherinomorph testis type. The short efferent ducts empty into a single longitudinal main duct in each testis. All species package sperm in the form of unencapsulated sperm bundles, which are referred to as spermatozeugmata. The mechanism of packet formation and the resulting spermatozeugmata are similar in all five species of Nomorhamphus and in four species of Dermogenys, with each spermatocyst releasing several small spermatozeugmata. In the other four species of Dermogenys, the mechanism of packet formation is similar, and each spermatocyst releases a single, large spermatozeugma. The spermatozeugmata of six species of Hemirhamphodon are unlike those seen in the other two genera, with five different sperm bundle types described herein. The unique sperm bundles of the viviparous halfbeaks are compared with those of the internally fertilizing but oviparous halfbeak genus, Zenarchopterus, discussed within a phylogenetic framework, and hypothesized to be independently derived within the Atherinomorpha.

Viviparity in the halfbeak genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae)

Gravid ovaries were examined histologically from two species of Nomorhamphus and 21 populations of Dermogenys. In addition, changes in dry‐weight throughout gestation are provided for 15 populations. The ovaries are paired organs running along the lateral body wall and are separated along most of their length. In all specimens examined, embryos are fertilized within the ovarian follicle. Viviparity in these species is divided herein into five categories designated types I–V. In types I and II the entire gestation period is intrafollicular, whereas in types III–V only the early stages of gestation are intrafollicular with the major period of development occurring in the ovarian lumen (intraluminal). Type I is characterized by the retention of a large amount of yolk throughout gestation. Superfetation is not observed. Populations of D. pusilla from Vietnam and Thailand decrease in dry‐weight throughout gestation. This, coupled with the slight vascularization of the yolk sac, suggests strict lecithotrophy. Populations of D. pusilla from Singapore and Bangladesh undergo an increase in dry weight and exhibit an increased vascularization of the yolk sac, suggesting a form of unspecialized matrotrophy. Type II is characterized by a small amount of yolk, an expansion of the coelomic cavity and pericardial sac, and a simple cuboidal epithelium on the general body surfaces. Superfetation occurs with up to three broods present within a single ovary. Dermogenys pusilla from Sabah, D. orientalis and Dermogenys sp. (Sulawesi) exhibit the type II form of viviparity. Dermogenys vivipara from the eastern Philippine islands of Culion and Busuanga exhibit characteristics considered intermediate between type I and II. These results are compared with those from other viviparous species exhibiting intrafollicular gestation. In species with types III–V (intraluminal gestation), developing oocytes are restricted to a distinct ridge of ovigerous tissue extending along the entire length of the ovary. Two species, D. viviparus (Luzon, Philippines) and Dermogenys sp. (Luzon) have the type III form of viviparity. In this form, oocytes are small (0.8–1.0 mm) with little yolk reserves and embryos, covered with a simple cuboidal epithelium and possessing an expanded belly sac, are retained within the follicles until a late fin‐bud stage. Type III embryos found within the ovarian lumen have a greatly expanded belly sac and remain covered by a simple cuboidal epithelium until parturition. Superfetation is present in these species with two broods observed simultaneously within a single ovary. Five species, D. megarrhamphus, D. weberi, D. viviparus (Jolo, Philippines), Nomorhamphus sp. (Sulawesi), and N. towoetii, were observed with the type IV form of viviparity. Embryos in this category are evacuated into the ovarian lumen prior to a fin‐bud stage and retain a large yolk mass throughout development. Superfetation is absent in these species. A differentform of viviparity (type V) is present in D. ebrardtii in which embryos appear to obtain nutrients through a form of oophagy and aldelphophagy (feeding on developing oocytes or less‐developed siblings). In all specimens with intraluminal development, atretic oocytes within the ovigerous ridge are abundant. These findings support the hypothesis that current species and generic limits may be artificial and underscores the potential of histological evidence for phylogenetic analysis of this group. J. Morphol. 234:295–317, 1997.

Ultrastructural study of embryonic and early adult germ cells, and their support cells, in both sexes of Xiphophorus (Teleostei:Poeciliidae)

The ultrastructure of the early spermatogonia in mature testes of the platyfish, Xiphophorus maculatus, was compared to that of oogonia in mature ovaries of X. maculatus and the related X. nigrensis. Both cell types were very similar and, characterized as being large, oval to round cells containing large, central nuclei with prominent nucleoli. Abundant mitochondria with sparse transverse cristae were located at one pole or around the nucleus. Annulate lamellae and electron-dense granular material (nuage) were present. Other organelles were not prominent. A female that had received a testis graft had testicular tissue containing mature spermatozoa within the ovary, indicating that cells were present that could develop along the male line. Special crosses were carried out to obtain all-male embryos of X. maculatus and all-female embryos of X. nigrensis. The ultrastructure of the germ cells in all embryonic gonads was similar to that of the adult cells. These results suggest the presence of sexually undifferentiated germ cells in the adult gonads of both sexes. The support cells investing all of these germ cells were also similar structurally and appeared to be undifferentiated.

Follicular placenta and embryonic growth of the viviparous four-eyed fish (Anableps)

In the four‐eyed fish, Anableps (Atheriniformes, Anablepidae), eggs are fertilized and embryos develop to term within the ovarian follicles. Development is highly matrotrophic. During gestation, the largest term embryo of A. anableps examined had grown to a total length of 51 mm and attained a dry weight of 149 mg. The postfertilization weight increase is 298,000%. The largest term embryo of A. dowi examined had grown to a total length of 77 mm and attained a dry weight of 910 mg. The postfertilization weight increase is 843,000%. Embryonic weight increases result from nutrient transfer across the follicular placenta. This structure is formed by apposition of the maternal follicular epithelium to absorptive surface cells of the embryos pericardial trophoderm. The latter, a ventral ramification of the pericardial somatopleure, replaces the yolk sac during early gestation. The external surface of the pericardial trophoderm develops hemispherical projections, termed vascular bulbs. Within each bulb, the vascular plexus of the trophoderm expands to form a blood sinus. Cells of the external surface of the bulbs possess microplicae. Microvilli are absent. During middle to late gestation, the juxtaembryonic follicular epithelium differentiates into two regions. One region consists of shallow, pitlike depressions within which vascular bulbs interdigitate in a “ball and socket” arrangement. Follicular pits are formed by the curvilinear distortion of the apical surfaces of follicle cells. The second region in contact with the dorsal and lateral surfaces of the embryo, is comprised of villous extensions of the hypertrophied follicular epithelium. In both regions, follicle cells appear to constitute a transporting rather than a secretory epithlium. In terms of percentage of weight increase, the follicular placenta of Anableps appears to be the most efficient adaptation for maternal‐embryonic nutrient transfer in teleost fishes and closely approaches the efficiency (1.2 × 106%) of oophagy and embryonic cannibalism in lamnoid sharks.