Sathyabama Chellappa

Harmful Phytoplankton Blooms and Fish Mortality in a eutrophicated reservoir of Northeast Brazil

The aim of this work was to study the eutrophication in the tropical freshwater ecosystems and the consequent cyanobacterial bloom formation and economical damage to fisheries and harmful effects to public health. Mass fish mortality due to toxin producing cyanobacterial blooms was registered during December 2003 in Marechal Dutra Reservoir, Acari/RN, Northeast Brazil. Phytoplankton and fish samplings were carried out on alternate days during the episode of fish mortality and monthly during January to June 2004. The cyanobacterial toxin was identified and quantified from the seston samples and liver of the dead fishes using the standard HPLC method. The results indicated that the toxic blooms of Cylindrospermopsis raciborskii and Microcystis aeruginosa were persistent for two weeks and represented 90% of the phytoplankton species assemblages. The lethally affected fishes were Oreochromis niloticus, Plagioscion squamosissimus, Cichla monoculus, Prochilodus brevis, Hoplias malabaricus and Leporinus friderici. The microcystin levels varied from 0.07 to 8.73µg L-1 the seston samples and from 0.01 to 2.59µg g-1in the liver samples of the fishes during the bloom period.

First record of Cymothoa spinipalpa (Isopoda: Cymothoidae) parasitizing the marine fish Atlantic bumper, Chloroscombrus chrysurus (Osteichthyes: Carangidae) from Brazil

This paper reports on parasitism in the marine fish Atlantic bumper Chloroscombrus chrysurus (Osteichthyes: Carangidae) by the cymothoid isopod Cymothoa spinipalpa as well as information pertaining to biological aspects. The fish samples were netted in the coastal waters of the Rio Grande do Norte, Brazil, and examined on a monthly basis from January to December 2006. A total of 30 adults of C. spinipalpa were found in 26 of the 204 Atlantic bumpers sampled. A prevalence of 12.8% and mean intensity of 1.15 parasites per fish were registered. The isopods were found in the branchial chamber and buccal cavity of the host. However, the parasitized and non-parasitized fish did not show any significant differences in their mean body mass, body length and condition factor. A positive correlation was found between the total length of female isopods and total body length of the hosts. The parasitic isopod females were larger than the males. Occurrence of males in the branchial chamber and the buccal cavity did not show any significant differences statistically, whereas the females showed a preference for the buccal cavity.

Morphohistology of the digestive tract of the damsel fish Stegastes fuscus (Osteichthyes: Pomacentridae).

This study investigated the morphohistology of the digestive tract and the mean intestinal coefficient of the damsel fish Stegastes fuscus captured from the tidal pools of Northeastern Brazil. The wall of the digestive tract of S. fuscus is composed of the tunica mucosa, tunica muscularis, and tunica serosa. The esophagus is short with sphincter and thick distensible wall with longitudinally folded mucosa. Mucous glands are predominant, and the muscular layer of the esophagus presented striated fibers all along its extension. The transition region close to the stomach shows plain and striated muscular fibers. Between the stomach and intestine, there are three pyloric caeca. The intestine is long and thin with four folds around the stomach. The anterior intestine presents folds similar to those of pyloric caeca. The estimated mean intestinal coefficient and characteristics of the digestive system of S. fuscus present morphological adequacy for both herbivorous and omnivorous feeding habits.

Ovarian development and spawning of Serra Spanish mackerel in coastal waters of Northeastern Brazil

The Serra Spanish mackerel, Scomberomorus brasiliensis is an important fishery resource of the Atlantic Ocean and is a major component of artisanal fisheries in northern and northeastern Brazil. Ovarian development and spawning period of S. brasiliensis were investigated using both macroscopic and histological techniques. Mean monthly values of GSI and ovarian maturation indicate that the main spawning period occurs during the rainy season.

Reproductive success and female preference in the amazonian cichlid angel fish, Pterophyllum scalare (Lichtenstein, 1823)

O acara bandeira, Pterophyllum scalaree um ciclideo nativo da Bacia Amazonica do Brasil, ee exportado como especie ornamental. Neste estudo foi investigada a importância da experiencia dos machos e do sucesso na reproducao anterior para escolha do parceiro. Para as investigacoes relativasa experiencia reprodutiva foram utilizados seis pares de machos (experientes e inexperientes) e seis femeas. Os machos foram colocados em aquarios, onde foram adicionadas as femeas (uma por aquario). A escolha do parceiro foi verificada atraves da permanencia das femeas junto a um dos machos. Para as investigacoes referentes ao sucesso reprodutivo foram testados seis pares de machos, cada par com um macho bem sucedido e outro mal sucedido na reproducao anterior, frente a uma femea bem sucedida. Foi observada a permanencia da femea com um dos machos, como indicativo de preferencia. Em seguida, cada femea foi pareada com um macho mal sucedido e avaliado o sucesso reprodutivo dos casais. As femeas preferiram machos maiores, mais agressivos, territoriais e experientes. As correlacoes entre agressividade dos machos, cuidado atraves da aeracao e sobrevivencia dos ovos foram significativas. Durante o cuidado com larvas a agressividade dos machos experientes foi significativa em relacaoa sobrevivencia delas. Alem disso, cuidado intrabucal e sobrevivencia das larvas mostraram correlacoes significativas em relacao ao cuidado realizado pelos peixes experientes, acasalados e isolados. Comparando a sobrevivencia de proles resultantes de acasalamentos com os machos experientes e inexperientes, foram observadas diferencas significativas. As correlacoes entre permanencia das femeas com machos bem sucedidos na reproducao e sobrevivencia de ovos e de larvas foram significativas. As femeas avaliam a capacidade e disposicao para investimento na criacao da prole atraves do comportamento de corte dos machos. Os machos experientes e bem sucedidos tem a preferencia das femeas e alcancam maior sucesso reprodutivo.

Reproductive Ecology of Prochilodus brevis an Endemic Fish from the Semiarid Region of Brazil

The commercially important migratory fish Prochilodus brevis is from the Neotropical region, and understanding the reproductive ecology of this potamodromous fish is essential for its conservation and management. This study investigated the length-mass relationship, sex ratio, length at first gonadal maturity, gonadal development stages, gonadosomatic index, condition factor, and reproductive period of P. brevis. Temporal distribution of rainfall, temperature, dissolved oxygen concentration, pH, and electrical conductivity of the water were related to the reproductive period of this fish. Rainfall seems to be the main environmental factor which modulates changes in limnological parameters and the timing of the spawning period of this fish. P. brevis migrates into lower reaches of the river to feed during the dry season and returns to the upper reaches during the rainy season to spawn. Inadequate facilities for migration create obstacles for spawning success of this ecologically important fish.

Cymothoa spinipalpa sp. nov. (Isopoda, Cymothoidae) a buccal cavity parasite of the marine fish, Oligoplites saurus (Bloch & Schneider) (Osteichthyes, Carangidae) of Rio Grande do Norte State, Brazil

Cymothoa spinipalpa sp. nov. (Isopoda, Cymothoidae) a buccal cavity parasite of the marine fish, Oligoplites saurus, is described on the basis of eight male specimens and one female. The fish hosts were captured in the coastal waters of Natal, Rio Grande do Norte State, Brazil. In the new species, the anterior margin of the cephalon is doubled ventrally over the bases of the antennae. In this respect, it resembles C. recifea Thatcher & Fonseca, 2005. It differs from that species, however, in being much smaller and having basal carinae on the pereopods 4 to 7 that are small and rounded (not large and pointed). Also, pleopods 2-4 lack the folds and pockets that are present in C. recifea. The new species can be distinguished from all known Cymothoa spp. by the mandibular palps which are entirely covered with small spines in adult males. The mancas of the new species resemble those of Cymothoa oestrum since they have elongate antennae but they are wider and have shorter uropods.

Mating system of the amazonian cichlid angel fish, Pterophyllum scalare

The species, Pterophyllum scalare distinguishes itself by its breeding behavior, involving competition for territory, sexual partners, courtship and parental care. The purpose of this study was to identify the mating system adopted by this species of fish. Twenty males and twenty females were observed under semi-natural and experimental conditions to test the hypothesis of serial monogamy. Under semi-natural conditions, after the third breeding cycle, the couples changed mates. Under experimental conditions, the couples changed partners after the first breeding cycle. Under experimental conditions, mate recognition was investigated through the preference of the females, indicated by the time they spent with the males. The females were available or not for courtship from new males, depending on their aggressiveness or submission. The larger and more aggressive males obtained new mating opportunities while the submissive males were rejected by the females. The mated fish were aggressive towards intruders in the presence of the mate, protecting their pair bond. In the interval between breeding cycles, the couples did not display aggression towards intruders, confirming the hypothesis of serial monogamy. Best mate selection by the females and the opportunity of new matings for both sexes influenced the reproductive success of this species.

Comportamento reprodutivo do acará bandeira, Pterophyllum scalare Cuvier & Valenciennes (Osteichthyes, Cichlidae)

Acara bandeira, Pterophyllum scalare Cuvier & Valenciennes, 1831 is a Neotropical cichlid fish, which has not been studied under a scientific approach. The objective of this work was to identify and describe the reproductive behaviour involved in the various phases of its reproductive cycle, such as territorial disputes and its establishment, substrate selection for spawning, courtship and mating, selection of mate and parental care. Twenty males and ten females of the study species were observed in the laboratory, over a period of six consecutive months. Behaviour descriptions resulting from these observations were analysed and the results show that the reproductive males are very agressive in the initial phase of reproduction. Agressiveness is a constant variable in encounters between territorial fishes, and possession of territory is of fundamental importance for reproduction of this species. Males with established territories were those which very successful in atracting the females during courtship. The selection of the females were influenced by the possession of territory, the type of substrate available for spawning and the body size. The fish preferred aquatic plants with broad leaves as an adequate substrate for spawning. It was observed that there was a short-term biparental care, before the eggs hatched, during which period the males played an important role in protecting them. After the eggs hatched, the male continued to protect the hatchling in his mouth, but played a lesser role, possibly to seek other females for mating so as to increase his reproductive output. Selection of a good mate by the female and the high degree of parental care were the factors which influence the reproductive success of the study species.

Biologia reprodutiva do peixe-donzela, Stegastes fuscus Cuvier, em arrecifes rochosos no nordeste do Brasil

Reproductive biology of the damselfish, Stegastes fuscus Cuvier, 1830 (Perciformes: Pomacentridae), was studied in the coastal rocky reefs of Buzios Beach, Nisia Floresta, Rio Grande do Norte, Brazil. The fish were captured on a monthly basis, and were measured, weighed, dissected and the gonads were removed, weighed and examined in order to separate males and females. Macroscopic characterization of the stages of gonadal maturation was carried out. A total of 549 samples were captured from October 2004 to September 2005. A higher frequency of females (78%) was registered in relation to males (22%). It was observed that 50% of the population of females and males initiated gonadal maturation with a body size of 6.2 cm and 7.0 cm respectively. In relation to absolute fecundity, the number of vitelogenic oocytes ranged from 1790 to 14780, with mean of 6832. The analysis of gonadosomatic relation indicated that the period of February to August was associated to a long phase of gonadal resting in males and females. Two peaks of partial spawning were registered during January and September-October. Five stages of gonadal maturation were identified through macroscopic analysis: immature, in maturation, mature, spent and resting.