Growth and nutritional condition of anchovy larvae on the west and southeast coasts of South Africa

Cape anchovy Engraulis encrasicolus is an ecologically and economically important pelagic fish species occurring along the coast of South Africa. A recent eastward shift in Cape anchovy distribution indicates that environmental conditions are becoming more favorable for the species on the east coast. This shift is particularly important in the sheltered Algoa Bay region, a nursery area for fish larvae. However, the relatively low productivity of the Agulhas Current Large Marine Ecosystem on the eastern coast of South Africa may result in an anchovy population in poorer nutritional condition and with slower growth rates than the west coast population. Using otolith and nucleic acid analyses, the growth rates of anchovy larvae from the western and southeastern coasts of South Africa were compared. The otolith analysis results indicated that, at any given age, individual growth rates for anchovy larvae were higher on the southeast coast than on the west coast. The RNA:DNA values also indicated that instantaneous growth rates of anchovy larvae were higher in Algoa Bay than on the west coast. At the time of sampling, chlorophyll and zooplankton productivity were higher at sampling sites in Algoa Bay than sites on the west coast, potentially due to favorable oceanographic features in the bay. As such, the results suggest that Algoa Bay is a suitable and potentially favorable nursery area for the early stages of anchovy, highlighting the importance of separate management of the southeast coast region in a changing world

Biologia, pesca i estat actual de l'anxova europea a la Mediterrània nord-occidental

Sense resu

Trophic ecology of small pelagic fish in the northwestern Mediterranean / Ecología trófica de peces pelágicos pequeños en el Mediterráneo noroccidental

[eng] In the northwestern Mediterranean anchovy and sardine are among the most ecologically and economically important species. Both species are planktivorous during all their life stages, which could alledgedly lead to expect an overlap of trophic niches. However, trophic interactions between the two species had been, until now, poorly studied. This thesis aims to examine and compare the feeding behaviors of sardine and anchovy at different stages of their development, and during different seasons, in the Gulf of Lions. In this work we have shown, through a detailed analysis of their diets and trophic dynamics, how these two species may interact with each other and with the environment, also considering the possibility of being affected by future climatic changes. We explained that in the sardine, withan almost strictly carnivorous diet at the end of their larval stage and shortly after metamorphosis, the development of their gill rakers and pyloric caeca allow a change in the diet when sardines reach 4 cm standard length (SL), and at 7 cm SL, with these structures already fully developed, they are able to feed on phytoplankton with total effectiveness. Juveniles of both species showed no interspecific trophiv competition, due to their marked differences in their gill rakers and pyloric caeca. We also showed, with the analysis of stable isotopes, that there is dietary change along the development of sardine and anchovy, and that the analysis of stable isotopes (δ13C and δ15N) is essential to identify potential prey, such as appendicularians, whose contribution to the diet is often underestimated when stomach contents are directly analysed. We assessed differences in the nutritional status of anchovy larvae found in summer and in December and estimated their growth rates. The nutritional condition of larvae in December was no different from the condition of larvae with the same size captured in summer. However, the higher daily growth rate of summer larvae suggests that sea temperature significantly influences the development of anchovy larvae. This thesis showed that anchovy and sardine have adapted their abilities and ecological habits in the northwestern Mediterranean to avoid interspecific competition, not just by shuffling their reproductive periods but also adapting their trophic behavior.[spa] En el Mediterráneo noroccidental, anchoa, Engraulis encrasicolus, y sardina, Sardina pilchardus, son las especies más importantes en términos de biomasa y de toneladas capturadas. La anchoa y la sardina son especies planctívoras que consumen, durante todas sus fases de desarrollo, un amplio rango de especies, lo que podría esperarse que se tradujera en un posible solapamiento de sus nichos tróficos. Sin embargo, las interacciones tróficas entre las dos especies habían sido, hasta el momento del inicio de esta tesis, escasamente estudiadas. Esta tesis tiene la finalidad de examinar y comparar, de manera exhaustiva, los comportamientos alimenticios de sardinas y anchoas en diferentes fases de su desarrollo, y durante distintas épocas del año, en el golfo de León, a la vez que pretende mostrar el análisis de algunos de los caracteres morfológicos relacionados con la alimentación de estas especies, como son las branquispinas y los ciegos pilóricos. En este trabajo hemos mostrado, a través de un detallado análisis de sus dietas y de sus dinámicas tróficas, de qué manera estas dos especies pueden interactuar entre ellas y con el medio, considerando especialmente la posibilidad de que se vean afectadas por las perturbaciones derivadas del cambio climático. El primer capítulo expone que en la sardina, con una dieta casi estrictamente carnívora al final de su etapa larvaria y hasta poco después de la metamorfosis, el desarrollo de sus branquispinas y ciegos pilóricos la habilitan para empezar a efectuar un posible cambio de dieta cuando alcanzan los 4 cm de longitud estándar (LE), y que al alcanzar los 7 cm LE ya ha desarrollado por completo dichas estructuras, por lo que es capaz de alimentarse de fitoplancton con total efectividad. En el segundo capítulo se observa que los juveniles de ambas especies no presentan competencia alimenticia interespecífica debido a sus ya marcadas diferencias en el número y disposición de sus branquispinas y en el número de ciegos pilóricos. El tercer capítulo muestra que , por un lado, que existe un cambio de dieta a lo largo del desarrollo de sardina y anchoa y, por otro, que el análisis de isótopos estables (en particular δ13C y δ15N) es esencial para identificar presas potenciales, como por ejemplo las apendicularias, cuya contribución a la dieta cuando se observan directamente los contenidos estomacales suele subestimarse. La aparición en diciembre de larvas de anchoa nos sugirió la idea de realizar un estudio que nos permitiera determinar la influencia del ambiente en el desarrollo y posterior reclutamiento de esta especie. Se evaluaron diferencias en la condición nutricional de ambas cohortes de larvas comparando su composición lipídica y se estimaron sus tasas de crecimiento a partir del análisis de los otolitos. La condición nutricional de las larvas de diciembre no difería de la condición de las larvas de igual tamaño capturadas en verano. Sin embargo, el hecho de que la tasa de crecimiento diario de las larvas de verano sí sea mayor que en diciembre induce a pensar que, ante una probable extensión del periodo de puesta debido a un calentamiento de las aguas superficiales, la temperatura sí influiría de manera significativa en el desarrollo de las larvas de anchoa. Esta tesis demuestra que anchoa y sardina han adaptado sus facultades y hábitos ecológicos en el Mediterráneo noroccidental con el fin de evitar la competencia interespecífica, no sólo alternando sus periodos reproductivos sino también adaptando sus comportamientos tróficos

Improved system identification using artificial neural networks and analysis of individual differences in responses of an identified neuron

Mathematical modelling is used routinely to understand the coding properties and dynamics of responses of neurons and neural networks. Here we analyse the effectiveness of Artificial Neural Networks (ANNs) as a modelling tool for motor neuron responses. We used ANNs to model the synaptic responses of an identified motor neuron, the fast extensor motor neuron, of the desert locust in response to displacement of a sensory organ, the femoral chordotonal organ, which monitors movements of the tibia relative to the femur of the leg. The aim of the study was threefold: first to determine the potential value of ANNs as tools to model and investigate neural networks, second to understand the generalisation properties of ANNs across individuals and to different input signals and third, to understand individual differences in responses of an identified neuron. A metaheuristic algorithm was developed to design the ANN architectures. The performance of the models generated by the ANNs was compared with those generated through previous mathematical models of the same neuron. The results suggest that ANNs are significantly better than LNL and Wiener models in predicting specific neural responses to Gaussian White Noise, but not significantly different when tested with sinusoidal inputs. They are also able to predict responses of the same neuron in different individuals irrespective of which animal was used to develop the model, although notable differences between some individuals were evident

O DEBATE SOBRE A REESTRUTURAÇÃO PRODUTIVA NO BRASIL

No Brasil, o processo de reestruturação produtiva vislumbra no final dos anos 1970, com a crise do modelo de desenvolvimento baseado na “substituição das importações” e se intensifica nos anos 1990, com a política neoliberal e a abertura econômica, acarretando transformações no processo produtivo, na gestão e organização do trabalho, bem como no espaço, produzindo “novosespaços industriais”.Neste texto, procuramos discutir a noção de reestruturação e fazer um panorama do debate da reestruturação produtiva no Brasil

Dataset for Predictive Control of Intersegmental Reflex Movements in an Insect

Matlab files containing of movements of the tarsus of a locust during displacement of the femoral chordotonal organ of the hind leg. The Readme.txt file gives full details of each file</span

Improved system identification using artificial neural networks and analysis of individual differences in responses of an identified neuron

We analyse the effectiveness of Artificial Neural Networks (ANNs) as a modelling tool for motor neuron responses. We used ANNs to model the synaptic responses of an identified motor neuron, the fast extensor motor neuron, of the desert locust in response to displacement of a sensory organ, the femoral chordotonal organ, which monitors movements of the tibia relative to the femur of the leg. The aim of the study was threefold: first to determine the potential value of ANNs as tools to model and investigate neural networks, second to understand the generalisation properties of ANNs across individuals and to different input signals and third, to understand individual differences in responses of an identified neuron. A metaheuristic algorithm was developed to design the ANN architectures. The performance of the models generated by the ANNs was compared with those generated through previous mathematical models of the same neuron. The results suggests that ANNs are significantly better than LNL and Wiener models in predicting specific neural responses to Gaussian White Noise, but not significantly different when tested with sinusoidal inputs. They are also able to predict responses of the same neuron in different individuals irrespective of which animal was used to develop the model, although notable differences between some individuals were evident.</span

Preliminary insight into the relationship between environmental factors and the nutritional condition and growth of Gilchristella aestuaria larvae in the upper reaches of South African estuaries

Estuarine systems play a critical role as nursery areas for some fish species. Nursery function, nevertheless, is likely to vary among estuaries, mostly due to differences in habitat quality. High quality nursery habitats are those in which growth and survival of early stages of fish are enhanced. The nutritional condition of larval fishes has vital implications for their mortality and growth, and thereby their recruitment. This study aimed to compare the nutritional condition of Gichristella aestuaria larvae, using individual RNA-DNA ratios and growth rates in the upper reaches of six estuaries in South Africa to find the environmental factors that better determine the nutritional condition of fish larvae. Physico-chemical factors as well as calorific value of zooplankton were used to correlate to fish body condition. Results showed that the larvae of G. aestuaria from the freshwater rich Gamtoos and the Sundays estuaries were in better nutritional condition than the larvae from other estuaries, while larvae from the Swartkops Estuary, a highly eutrophic system, presented the worst nutritional condition of all studied larvae. Salinity and the abundance of zooplankton were the major factors determining the nutritional condition of G. aestuaria larvae in these warm temperate estuaries. In addition, our results suggest that the match-mismatch hypothesis might also be important in estuarine systems. This study represents one of the few studies worldwide that applied a multispecies growth model for fish larvae in warm temperate estuarie