Larval development ofNeopisosoma neglectum werding, 1986 (Decapoda: Anomura: Porcellanidae) under laboratory conditions

The complete larval development of the porcellanid crabNeopisosoma negluctum Werding, 1986, was studied under laboratory conditions. At 27°C, the megalopa appeared after 9 days. The development consists of a transitory prezoea, two zoeal stages and a megalopa stage. The larvae exhibit telsonal features which places them in thePetrolisthes-group of porcellanid larvae. Larval morphology gives no additional support for the status ofNeopisosoma as an independent genus.     

Larval development of Brachynotus gemmellari (Rizza, 1839) (Brachyura, Grapsidae) reared under laboratory conditions

The complete larval development of the grapsid crab Brachynorusgemmellari (Rizza, 1839) was obtained by culture in the Iabomtoiy.Five zoeal stages, the megalopa and the first crab stage aredescribed and illustrated. Larval development from hatchingto first crab took 26 days at 20C. The morphological charaeiarsof the larvae of B.gemmellari are compared with those of otherknown larvae of the genus Brachynosus.     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Larval development of Hexapanopeus caribbaeus (Stimpson, 1871) (Crustacea, Decapoda, Xanthoidea, Panopeidae) reared under laboratory conditions

The genus Hexapanopeus Rathbun, 1898 contains eight species,of which three are found in the Brazilian coast. The larvaldevelopment of two of these species has already been studiedin the laboratory. This article describes in detail the morphologyof the complete larval stages of Hexapanopeus caribbaeus rearedunder laboratory conditions, and the morphology is comparedwith that of the larvae of the other species of the same genus.     

Male-female Parental Roles in Sarotherodon galilaeus (Pisces: Cichlidae)

Sarotherodon galilaeus is a predominantly biparental, sexually monomorphic mouthbrooder. 15 spawnings of pairs in the weight range 150–450 g were observed in aquaria. Only clutches of females larger than 320 g were reared jointly; with those of smaller females, the first fish to pick up eggs brooded alone, while the comparatively few eggs left for the second fish were invariably eaten. The latency after which eggs were picked up increased with the duration of spawning and indirectly with fish size. This increase was larger in males than in females, so large males started to collect eggs later than their mates. In small pairs (female weight < 200 g), by contrast, the male would pick up eggs first and carry them alone. This is the case in a smaller congeneric species, S. melanotheron, indicating that the apportioning of broodcare is based on a unitary, size-dependent mechanism among Sarotherodon. Yet picking-up order was not entirely determined by these equations. Some fish did not show any reaction towards the eggs and occasionally males became care-givers despite expected longer latency, seemingly because of aggressive dominance.     

Evolutionary relationships within three Tilapiine genera (Pisces: Cichlidae)

Species of the cichlid genera Tilapia, Sarotherodon and Oreochromis were studied by electrophoresis at 25 enzyme loci. The levels of similarities within and between genera, and the distribution of genetic identities at individual loci are similar to those found in other fish species. The evolutionary relationships between the species remains equivocal, and it is still not possible to decide between the hypotheses of Trewavas (1980) or that of Peters & Berns (1978, 1982). Further work needs to be undertaken on additional Tilapia and Sarotherodon species. The unexpected relationship of O. jipe to the other Oreochromis species is probably the strongest argument against Trewavas' hypothesis. But the close similarity of the maternal mouth brooders to each other, and the closer relationship of S. galilaeus to the Oreochromis species than to the Tilapia does not favour the hypothesis of Peters & Berns (1982). The difficulties in obtaining pure species from the wild due to widespread introduction of non-endemic species are likely to hinder progress in evolutionary and aquacultural studies.     

Larval development of the Indo-Pacific perciform fish,Centrogenys vaigiensis (Pisces: Centrogeniidae)

Based on seven larvae from northern Australia, development ofCentrogenys vaigiensis—a species of uncertain phylogenetic affinities—is described for the first time. Identification was established from meristic and osteological characters. Development is characterized by few morphological specializations and is apparently completed at a small size (ca 5 mm standard length). Larvae are deep-bodied and compressed, with very limited head spination (small spines on preopercle, subopercle, opercle and supracleithrum). Fin development takes place at about the time of notochord flexion, and is complete at about 4.3 mm, with the exception of anal spine three, which does not fully transform from a soft ray until after settlement. Fin spines are short, smooth and weak. Larvae are apparently limited to near-shore, shallow marine waters, and based on the size of what are apparently settlement-stage larvae, the pelagic period may be short.     

Freiwasserbeobachtungen an Tilapien (Pisces,Cichlidae) in Ostafrika

T. grahami ♂♂ haben in Kolonien dicht beieinander liegende Reviere; sie beziehen sie frühmorgens bei völliger Dunkelheit und verlassen sie am späten Nachmittag wieder. Einige daraufhin beobachtete ♂♂ waren immer in der gleichen Grube zu finden. Es wird angenommen, daß dies generell gilt. Kämpfe sind äußerst selten. Revier-♂♂ kämpfen durchschnittlich nur etwa 2mal pro Woche. Revierlose ♂♂ rufen öfter Kämpfe hervor, und da Kämpfe auch nachts zu bemerken sind, ist eine teilweise Unabhängigkeit des Kämpfens vom Revierverhalten zu folgern. Ersatzhandlungen fürs Kämpfen sind das Graben und das Vertreiben von Jungfischen. Es wird angenommen, daß diese Handlungen wegen der beengten Lebensbedingungen einen positiven Selektionswert haben. Aus den gleichen Gründen sind wohl Balzhandlungen reduziert, die Laichdauer auf eine Sekunde zusammengeschrumpft und Jungfische früher als in jeder anderen Cichlidenart geschlechtsreif. Diese Frühreife hat bei T. alcalica zu einem Kampfgleichgewicht zwischen sehr unterschiedlich großen ♂♂ geführt. Sonst zeigt die Art keine Unterschiede im Verhalten zu T. grahami. Bei den Geißeltilapien T. variabilis und T. rukwaensis kann die Reviergröße in sehr weiten Grenzen schwanken. In großen Revieren schwimmen die ♂♂ viel an ihren Reviergrenzen entlang, ihr Gebiet auf diese Weise gegen Reviernachbarn markierend und auf ♀♀ hin kontrollierend. In kleinen Revieren bietet sich mehr ein Bild wie bei den Sodatilapien T. grahami und T. alcalica. Aus dem Vergleich der Gruben, der Balz und des Laichens von Soda- und Geißeltilapien lassen sich verwandtschaftliche Beziehungen zwischen beiden Gruppen erschließen. Es werden also vor allem Revierverhaltensweisen in ihrer Anpassung an wechselnde Umweltbedingungen beschrieben und Balzhandlungen zur Klärung verwandtschaftlicher Beziehungen verwandt.     

A preliminary investigation of sex change inPseudotropheus lombardoi (Pisces: Cichlidae)

Synopsis Peters (1975) suggested the possibility of adult sex change in certain cichlids of Lake Malawi. When adultPseudotropheus lombardoi in male coloration were found mouthbrooding eggs under natural conditions in Lake Malawi, one of the possible explanations for this female-type behaviour was that sex change had occurred, but with the retention of male coloration. Behavioural investigations based on current models of social systems in sex-changing species were conducted in an attempt to substantiate this hypothesis. These observations were supplemented by an histological examination of the gonads of individuals of both sexes. A pronounced advantage in the mating success of dominant males over non-dominant males was noted. Similarly, large females had a greater reproductive success than smaller females. Thus, the possibility that sex change occurred inP. lombardoi following the size advantage model (Warner 1975) was investigated. However, histological studies did not provide conclusive evidence of sex change; only undeveloped oocytes were found in the testes of all males examined. It is postulated that gonads of maleP. lombardoi pass through an intersexual juvenile period. Later, testicular elements dominate within a gonad still containing immature oocyte tissues. It is further suggested that femaleP. lombardoi are dimorphic, some having male coloration and others having female coloration.     

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae)

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.     

Vergleichende Untersuchungen zur Elternbindung von Tilapia-Jungfischen (Cichlidae,Pisces)

• 1 Das Eltern-Bindungsverhalten junger Tilapien wird an einem charakteristischen Beispiel dargestellt (Abb. 5). Es wird von einer allgemeinen Orientierungsbewegung abgeleitet (Bindungsobjekt als “optische Marke”), in welche spezielle Verhaltensweisen ‘eingebaut’ sind (Bindungsobjekt als Kontakt-Gegenstand). Anhand photographisch aufgenommener Bewegungsbahn-Protokolle (Abb. 6) wird das Verhaltensmuster der drei Tilapia-Arten tholloni (Substratbrüter), nilotica (weibl. Maulbrüter) und heudeloti macrocephala (männl. Maulbrüter) eingehend untersucht und in fünf verschiedene Verhaltenstypen eingeteilt.
• 2 Die quantitative Untersuchung der angeborenen Reaktionen auf verschiedene Eigenschaften des Bindungsobjektes setzt eine genaue Kenntnis der inneren Faktoren voraus, die Einfluß auf die Bindungsbereitschaft haben. Unter diesen sind vor allem endogene Rhythmen und Reifungsvorgänge von Bedeutung. Die Auswirkung endogener Rhythmen wird bei T. nilotica am Kontaktverhalten und dem Aufenthalt in einer Attrappenöffnung (künstliche Mundhöhle) untersucht. Kontaktzahl (Abb. 7) und Kontaktdauer (Abb. 10) erreichen auch im Dauerlicht am Abend und am Morgen etwa doppelt so hohe Werte wie mittags und nachts. Ähnlich verhält es sich mit dem Aufsuchen der Attrappenöffnung (Abb. 9). Die Dauer des Aufenthalts im Attrappeninnern dagegen (Abb. 8) scheint einer einfachen Tag-Nacht-Periodik zu unterliegen. Aufgrund innerer Reifungsvorgänge macht das Bindungsverhalten der Tilapia-Jungfische verschiedene Veränderungen durch, beginnend mit einer sensiblen Phase, innerhalb (und nur innerhalb!) derer eine Bindung an ein Elternobjekt möglich ist. Bei allen untersuchten Tilapia-Arten dauert die sensible Phase unter den geschilderten Zuchtbedingungen vom Beginn der Schwimmfähigkeit bis etwa zum 12. Tag. Danach kann keine Bindung mehr Zustandekommen, doch kann ein bereits gebundenes Tier erheblich länger gebunden bleiben: Bindungsphase (Abb. 11). Auch T. heudeloti macrocephala durchläuft die sensible Phase. Die Jungen befinden sich aber zu dieser Zeit gewöhnlich noch als schwimmunfähige Larven im Maul des Vaters, so daß sie keine Möglichkeit haben, sich zu binden. Durch Versuche mit Jungfischen, deren Larvalzeit durch Dotterpunktion soweit verkürzt wurde, daß sie schon am 9. und 10. Tag schwimmfähig waren, konnte nachgewiesen werden, daß heudeloti m. in qualitativer Hinsicht nahezu das gleiche angeborene Bindungsverhalten besitzt, wie die beiden anderen Tilapia-Arten (Abb. 13–16). In den ersten drei Tagen der sensiblen Phase schließen sich tholloni-Jungfische in größeren Gruppen besonders gut an Elternobjekte an (Abb. 11); als Einzeltiere (Abb. 12) oder in kleinen Gruppen jedoch nur mäßig. Dies dürfte damit zusammenhängen, daß tholloni (und andere Substratbrüter) — bedingt durch die geringe Eigröße — das Freileben bereits auf einer Entwicklungsstufe beginnen, die noch durch manche larvale Merkmale gekennzeichnet ist. So erfolgt die Fortbewegung anfänglich noch weitgehend mittels desselben Bewegungstyps, der dem gleichmäßigen “Schwänzeln” (wriggling) der Larven zugrunde liegt. Dadurch wird die Möglichkeit zu gerichteter Fortbewegung, welche eine wesentliche Voraussetzung für die Bindung an optische Marken ist, beeinträchtigt. In Gruppen wird dieser Mangel offenbar durch einen noch unbekannten Schar-Effekt (vermutlich olfaktorisch) kompensiert.
• 3 Die Bedeutung verschiedener Merkmale für die größere oder geringere Eignung eines Gegenstandes als Bindungsobjekt wurde mit künstlich aufgezogenen tholloni- und nilotica-Gruppen durch Sechsfachwahl (Abb. 4) quantitativ bestimmt. Versuche, in denen 6 ununterbrochen senkrecht auf- und abschwingende schwarze Kugeln mit unterschiedlicher Frequenz bei gleicher Amplitude und umgekehrt geboten wurden (Abb. 19, 20), ergaben, daß erstens zwischen tholloni und nilotica keine wesentlichen Unterschiede bestehen und daß zweitens die wirksamste Bewegung mit 76 mm/Sek. unerwartet hoch liegt. Im elterlichen Führungsverhalten findet sich dazu — jedenfalls als Dauerreiz —nichts Vergleichbares. Entsprechende Versuche zur Frage der Bedeutung von Attrappenfarbe und -helligkeit (Tab. 1; Abb. 21, 22) ergaben: tholloni und nilotica unterscheiden zwischen Farbe und Helligkeit. Im dunklen Bereich bevorzugen sie die Farben, im Hellen dagegen die Graustufen. Die wirksamsten Farben (tholloni: Grün; nilotica: Schwarz, Blau und Grün) kommen in der Färbung der Eltern nicht vor. Umgekehrt sind gerade diejenigen Farben, die der elterlichen Tracht am nächsten kommen (tholloni: Rot; nilotica: Gelb und Hellgrau), nur schwach wirksam, bei tholloni sogar am schwächsten von allen gebotenen Farben und Graustufen.

     

Bi-parental mouth brooding in Tilapia galilaea (Pisces, Cichlidae)

New evidence shows that Tilapia galilaea (Artédi) is almost certainly a bi-parental mouth brooder throughout its range, and that this habit is not confined only to races found in Israel. Previous classification of this species as a maternal brooder in Africa appears to be based on lack of observations; it is the only member of the genus definitely known to be a bi-parental brooder. The size of the eggs and the development of their adhesive stalk system is intermediate between those of substrate spawners and mouth brooders. Among the latter the adhesive stalk system of the only paternal brooding species is rudimentary but it is entirely absent in the maternal brooding species. The conclusion is drawn that maternal and paternal mouth brooders did not evolve directly from substrate spawners but independently from bi-parental brooders.     

Citogenetic characterization of the tropical freshwater fish Parachromis managuensis (Pisces: Cichlidae)

To describe the cytogenetics of the jaguar cichlid fish Parachromis managuensis, we collected eight males and 13 females in Villahermosa, Tabasco, México. The specimens were processed with standard cytogenetic techniques (slightly modified), and high quality fields of chromosomes in mitosis and meiosis were obtained; 14 of these fields were analyzed by meristics and statistics methods. The specimens presented a diploid modal number of 2n = 48 chromosomes, which is similar to the number reported for others Central American cichlids; five pairs were submetacentric-metacentrics (biarmed) and 19 were subtelocentric-telocentric (uni-armed), giving a fundamental number (NF) of 58. The haploid number was confirmed by counting meiotic fields in metaphase I. There was not evidence of heteromorphism: sexual chromosomes were not identifiable.     

Naphthalene-induced changes in carbohydrate metabolism in Sarotherodon mossambicus Peters (Pisces: Cichlidae)

Sarotherodon mossambicus Peters was exposed to naphthalene concentrations ranging from 7.9 to 0.92 mg/l for periods ranging from 4 days to 10 weeks and changes in glycogen, glucose, pyruvic acid and lactic acid contents of liver and muscle were studied. While glucose levels remained unaffected, major effects could be seen in the other constituents following both lethal and sublethal naphthalene treatment. Whereas glycogen and pyruvic acid levels showed considerable reduction, lactic acid levels increased markedly. These changes are indicative of a metabolic stress leading to a shift to anaerobic metabolism. The effects do not appear to be related to the feeding and growth rates of the naphthalene-intoxicated fish.     

Larval development of Crangon hakodatei Rathbun (Decapoda: Crangonidae) reared in the laboratory

Complete larval development of Crangon hakodatei Rathbun isdescribed, based on material hatched in the laboratory fromovigerous females. The species has six zoeal stages and onepostlarval stage. The morphological characters of the larvaland postlarval stages are described with illustrative figuresand compared with those of two congeneric species. The zoealstages of C. hakodatei can be distinguished from those of otherCrangon species in the number of segments of the antennule peduncle,the number of setae on the antennal scale and basis of the maxillipeds,and the stages of appearance of pereiopods. The first zoealstage in the seven species of Crangon are compared and an annotatedkey for distinguishing them is also provided.