Luciano Neves dos Santos

Fish colonization of artificial reefs in a large Neotropical reservoir: material type and successional changes

Artificial reefs have barely been used in Neotropical reservoirs (about five studies in three reservoirs), despite their potential as a fishery management tool to create new habitats and also to understand fish ecology. We experimentally assessed how reef material (ceramic, concrete, and PVC) and time modulated fish colonization of artificial reefs deployed in Itaipu Reservoir, a large reservoir of the mainstem Paraná River, Brazil. Fish richness, abundance, and biomass were significantly greater in the reef treatments than at control sites. Among the experimental reefs, ceramic followed by the concrete treatments were the materials most effectively colonized, harboring the majority of the 13 fish species recorded. Although dependent on material type, many of the regularities of ecological successions were also observed in the artificial reefs, including decelerating increases in species richness, abundance, mean individual size, and species loss rates with time and decelerating decreases of species gain and turnover rates. Species composition also varied with material type and time, together with suites of life history traits: more equilibrium species (i.e., fishes of intermediate size that often exhibit parental care and produce fewer but larger offspring) of the Winemiller-Rose model of fish life histories prevailed in later successional stages. Overall, our study suggests that experimental reefs are a promising tool to understand ecological succession of fish assemblages, particularly in tropical ecosystems given their high species richness and low seasonality.

Genetic divergence among invasive and native populations of the yellow peacock cichlid Cichla kelberi

This study used the hypervariable domain of the mitochondrial DNA (mtDNA) control region (CR) to assess the genetic divergence among native and invasive populations of Cichla kelberi, which is considered the first peacock cichlid introduced and established throughout Brazil and is among the most invasive populations of this genus worldwide. The maximum likelihood tree based on 53 CR sequences with strong bootstrap support revealed that C. kelberi forms a monophyletic clade, confirming that all 30 C. kelberi studied belong to this morphotype. Additionally, the haplotype analysis of the C. kelberi sequences from 11 sampling sites revealed that invasive populations are much less diverse than native ones and largely dominated by a single haplotype that prevailed in reservoirs at the Paraíba do Sul River basin. Two haplotypes were recorded exclusively in an invasive population at Porto Rico, southern Brazil, and one private haplotype was detected in two reservoirs from Paraíba do Sul (Pereira Passos and Paracambi), suggesting more than one introduction event and that native populations should be better evaluated to encompass the entire genetic diversity of native C. kelberi. The possible route and pathways of C. kelberi introduction are also briefly discussed.

Toxicity of benthic dinoflagellates on grazing, behavior and survival of the brine shrimp Artemia salina

Harmful algae may differently affect their primary grazers, causing sub-lethal effects and/or leading to their death. The present study aim to compare the effects of three toxic benthic dinoflagellates on clearance and grazing rates, behavioral changes, and survival of Artemia salina. Feeding assays consisted in 1-h incubations of brine shrimps with the toxic Prorocentrum lima, Gambierdiscus excentricus and Ostreopsis cf. ovata and the non-toxic Tetraselmis sp. Brine shrimps fed unselectively on all toxic and non-toxic algal preys, without significant differences in clearance and ingestion rates. Acute toxicity assays were performed with dinoflagellate cells in two growth phases during 7-h to assess differences in cell toxicity to A. salina. Additionally, exposure to cell-free medium was performed to evaluate its effects on A. salina survival. The behavior of brine shrimps significantly changed during exposure to the toxic dinoflagellates, becoming immobile at the bottom by the end of the trials. Dinoflagellates significantly affected A. salina survival with 100% mortality after 7-h exposure to cells in exponential phase (all treatments) and to P. lima in stationary phase. Mortality rates of brine shrimps exposed to O. cf. ovata and G. excentricus in stationary phase were 91% and 75%, respectively. However, incubations of the brine shrimps with cell-free medium did not affect A. salina survivorship. Significant differences in toxic effects between cell growth phases were only found in the survival rates of A. salina exposed to G. excentricus. Acute exposure to benthic toxic dinoflagellates induced harmful effects on behavior and survival of A. salina. Negative effects related to the toxicity of benthic dinoflagellates are thus expected on their primary grazers making them more vulnerable to predation and vectors of toxins through the marine food webs.

When habitat complexity increases predation risk: experiments with invasive and neotropical native fishes

We tested the predator-prey relationships between a native piscivore (Salminus brasiliensis) and introduced and native fish species of the ParanaRiver, Brazil. We hypothesised that S. brasiliensis can exert biotic resistance against invasive fishes but not at the same degree for all species. Three invasive (Cichla piquiti, Oreochromis niloticus and Ictalurus punctatus) and two native (Astyanax altiparanae and Prochilodus lineatus) species were offered as prey to S. brasiliensisin 300Laquaria trials atthree levels of cover(0%, 50% and100% of artificial macrophytes).S. brasiliensis hadagreaterabilitytocapturepreyincomplexhabitats,sopredationsuccessdidnotdecreasewithhabitatcomplexityand evenincreasedonI.punctatus.Preysurvivalwasvariablethroughtimeandamongspecies,beinghighforI.punctatus.The three most consumed species (P. lineatus, C. piquiti, and O. niloticus) were less active and occupied the aquaria surfaces, changing strongly their behaviour with habitat complexity. Except for P. lineatus and C. piquiti,S. brasiliensis preferably preyed on smaller individuals of the other species. Our experiments support that S. brasiliensis is an interesting candidate to resist the invasion by C. piquiti and O. niloticus but not to control the abundance of I. punctatus. Additional keywords: biotic resistance, invasive species, ParanaRiver basin, predator-prey interactions, Salminus brasiliensis.

Experimental assessment of the effects of a Neotropical nocturnal piscivore on juvenile native and invasive fishes

A relacao predador-presa entre juvenis de pintado Pseudoplatystoma corruscans (piscivoro nativo) e jovens do ano de especies nativas e invasoras de peixes da bacia do rio Parana, Brasil, foi testada experimentalmente. Tres especies de peixe invasoras (o tucunare Cichla piquiti, a tilapia do Nilo Oreochromis niloticus e o bagre do canal Ictalurus punctatus) e duas nativas (o lambari do rabo amarelo Astyanax altiparanae e o curimbata Prochilodus lineatus) foram oferecidas como presa para P. corruscans em microcosmos, com tres tratamentos de complexidade de habitat (0%, 50% e 100% de cobertura por estruturas submersas). A sobrevivencia de presas variou ao longo do tempo e entre especies (C. piquiti < O. niloticus < A. altiparanae < P. lineatus < I. punctatus), sendo governada, em grande parte, por diferencas especies-especificas no comportamento das presas, mas tambem pelo tamanho e defesas morfologicas das mesmas. A complexidade de habitat nao afetou diretamente a piscivoria de P. corruscans, mas, na presenca do predador, algumas especies-presa alteraram seu comportamento quanto ao uso de micro-habitat e grau de agregacao entre os niveis de complexidade de habitat. Pseudoplatystoma corruscans predou preferencialmente sobre os individuos menores das especies invasoras que apresentaram estruturas morfologicas defensivas pouco desenvolvidas e que nao formavam cardume. Em geral, os resultados obtidos contrastam com os de um experimento analogo, no qual foi usado um piscivoro diurno, sugerindo que piscivoros noturnos predam preferencialmente sobre especies de peixes diferentes (de habitos mais diurnos) e que sao menos afetados pela complexidade estrutural de habitats. Os resultados obtidos sugerem que a recuperacao de populacoes nativas de P. corruscans poderia contribuir para o controle de algumas especies de peixes introduzidas no rio Parana, especialmente C. piquiti e O. niloticus, dos quais se espera que o cuidado parental seja reduzido ou nulo a noite.

Preferência alimentar de juvenis de lambari-cachorro, Oligosarcus hepsetus, em relação a duas espécies de presas de peixe em ambiente controlado

This study was based on previously published data on natural diet of the pike characin, Oligosarcus hepsetus in a reservoir at Southeastern Brazil, and thus tested the feeding preference of this carnivore using microcosm experiments. The experiments were conducted in aquariums, in January 2011. Predators were collected in a tributary of the Paraiba do Sul River, while preys: Tilapia rendalli and Astyanax fasciatus were obtained of fish farms. We tested the feeding preference by pike characin in relation to prey size and species, and the results were compared to prey energy. Juvenile pike characin predated preferentially on tilapias with lower body length height, whereas no clear pattern of consumption was observed for lambaris. Tilapias were preferentially predated at experiments with standardized prey body length, whereas no feeding preference was recorded on any prey species at experiments with standardized prey body height. Energetic differences between prey species seem to be less important than morphological differences for the feeding preference of pike characin.

Abundance of invasive peacock bass increases with water residence time of reservoirs in southeastern Brazil

Neotropical freshwater ecosystems are experiencing a great expansion in the number of invasive species, which is especially alarming since this region harbours 30% of the world’s fish biodiversity with high levels of endemism. We aimed to evaluate the main predictors of peacock basses (Cichla spp.) abundance outside their native range, which are the Amazon and Tocantins-Araguaia river basins. We used multivariate ordination techniques and multimodel inference to analyse peacock basses abundance in twelve reservoirs of the Paraíba do Sul river basin, southeastern Brazil. Interestingly, reservoirs at higher (southernmost) latitudes, located in more populated areas, had higher water temperature and lower turbidity, due to increased water residence time, and these three variables were also positively correlated with abundance of this warm-water invasive fish. Habitat structure was less important in explaining peacock basses abundance, which was not significantly related to biotic factors (fish species richness and time since peacock basses introduction). We hypothesize that the observed effects of reservoir management on limnological features and peacock bass abundance, particularly water residence time (as a mediator of temperature and turbidity), may apply to other Neotropical basins and could influence the impact of this invader.

Response of fish assemblage structure to changing flood and flow pulses in a large subtropical river

Fish assemblages recorded from August 2010 to July 2013 in two lotic and lentic environments of the Middle Parana River floodplain were studied in the light of flood and flow pulse variations. Three flood pulses occurred during the period of study, each with a different magnitude, duration and timing. Instead four flow pulses were recorded during this period. The varied hydrological conditions had an influence on the ichthyofauna. The fish species richness in both lentic and lotic habitat was negatively correlated with the maximum water level and fish assemblages were spatially and temporally structured according to their different reproductive strategies. Long- and short-distance migratory species were dominant after the flood pulse of the highest intensity and longest duration, whereas sedentary fish and internal fertilisation prevailed during flow pulses and lower flood pulses. Fish assemblage similarity was generally low between habitats during flood and flow pulses, but increased after those events depending on their magnitude, duration and timing. Apparently, flow pulses would also function like floods, as mechanisms of spatio-temporal structuring of fish assemblages.

Evaluation of factors associated with dynamics of Cichla ocellaris invasion of the Upper Paraná River floodplain system, Brazil.

Invasion by Cichla ocellaris was studied in the Upper Parana River floodplain. Generalised linear models and the Akaike Information Criterion (AIC) were applied to standardised gill-net catch data (CPUE), with years, rivers, secchi depth, and their respective interactions. Generalised additive models and AIC were used to evaluate relationships of CPUE for C. ocellaris with standard length, sampling year and secchi depth. C. ocellaris was first recorded in 1992 in the Parana and Ivinheima Rivers. Nevertheless, the CPUE of individuals was very low in the latter until 2000, and the species was not recorded from the Baia River until 2000. In 2001, CPUE of C. ocellaris greatly increased (from 20 to 140) in all three rivers, and this coincided with changes in hydrology and suspended sediment. Greater secchi depth is thought to benefit foraging by these visually oriented, diurnal piscivores. The estimated annual growth rate for local populations was 21% for the Parana, 42% for the Ivinheima, and 73% for the Baia Rivers. Consequently, relative to other populations, C. ocellaris of the Baia River and, to a lesser degree, the Ivinheima River, appear to be less influenced by density-dependent factors given their more recent invasions of those areas.

Reproductive biology of Cetengraulis edentulus (Cuvier, 1829), the major fishery resource in Guanabara Bay, Brazil

Cetengraulis edentulus is a broadely distributed engraulid in Southwest Atlantic, currently accounting for the main fish species commercially exploited at Guanabara Bay, Brazil. This study aimed to extend the knowledge on reproduction of C. edentulus at Guanabara Bay and to test whether some descriptors of reproductive activity, especially the gonadosomatic index (GSI), and the index of reproductive activity (IRA) changed among seasons. A total of 978 C. edentulus specimens were retrieved from purse seine commercial landings at Conservas Rubi S.A. company, in Sao Goncalo city, RJ. Subsamples of 90-120 individuals were collected from bimonthly yields between July 2010 (winter) and June 2011 (autumn). Most fish were adults (120-170 mm TL), in response to the high selectivity of commercial fisheries. All descriptors indicated a broad spawning period (late winter to spring), peaking in November, suggesting this is the critical period to protect C. edentulus stocks from overfishing at Guanabara Bay. Fecundity averaged 12,720 oocytes and was positively related to fish size, GSI and fullness index, indicating that preserving larger individuals (TL > 160 mm) could contribute significantly to the reproductive success of C. edentulus, since they produce more oocytes. Cetengraulis edentulus e um engraulideo amplamente distribuido no Atlântico Sudoeste, sendo um importante recurso comercialmente explorado na baia de Guanabara, Brasil. O presente estudo teve como objetivo ampliar o conhecimento sobre a reproducao de C. edentulus na baia de Guanabara e testar quais descritores da atividade reprodutiva, especialmente o indice gonadossomatico (IGS) e o indice de atividade reprodutiva (IAR) se modificaram ao longo das estacoes do ano. Um total de 978 individuos de C. edentulus foram capturados pelo metodo de rede de cerco da frota comercial no cais da empresa Conservas Rubi S.A., na cidade de Sao Goncalo, RJ. Subamostras de 90-120 individuos de C. edentulus foram coletados bimestralmente durante o periodo de julho de 2010 (inverno) e junho de 2011 (outono). A maioria dos individuos foram adultos (120-170 mm CT), em resposta a alta seletividade das capturas comerciais. Todos os indices indicaram um amplo periodo reprodutivo (final do inverno e primavera), com pico em novembro, sugerindo que este seria um periodo critico para preservar os estoques de C. edentulusda sobrepesca na baia de Guanabara. A fecundidade media foi de 12720 ovocitos e foi positivamente relacionada com tamanho do peixe, IGS e indice de replecao, indicando que preservar maiores individuos (CT > 160 mm) poderia contribuir significativamente para o sucesso reprodutivo de C. edentulusna area, visto que esses individuos produzem um maior numero de ovocitos.