Respiration von Gobiusculus flavescens und Pomatoschistus minutus bei spontaner Schwimmaktivitaet

The respiration rate of two gobiid species was correlated with a simple activity parameter ('swimming' or 'not swimming') which can also be quantified in situ. The study is intended to give a base for estimating the energy demand of free-living gobies. In laboratory experiments, swimming activity of two-spotted gobies (Gobiusculus flavescens) was highest during daytime, with a peak at dawn. In contrast, sand gobies (Pomatoschistus minutus) were most active during the night. Due to a lower specific density of the body tissues and a smaller volume of the swimbladder, underwater weight of P. minutus was twice as high as that of G. flavescens. Nevertheless, no significant difference in energy demand could be found between the species. In both species, swimming fish consumed twice as much oxygen as those resting on the ground. During feeding on Artemia nauplii, the respiration rate of the planktivorous two-spotted goby increased to about three times standard metabolism. Gobies predominantly swim with their pectoral fins (labriform swimming). Between the two species, there was no significant difference in the area of the pectoralia. The caudal fin is used for fast-starts (attack, evasion). The increase of the caudal fin area as function of body length was higher in G. flavescens than in P. minutus. At a total length of 45 mm, the area of the caudal fin was nearly 1/5 bigger in two-spotted goby than in sand goby. (orig.)Available from TIB Hannover: RN 3292(252) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Settling velocity of faecal pellets of gilthead sea bream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.) and sensitivity analysis of measured data using a deposition model

Settling rates of faecal material from three size categories of cultured gilthead sea bream, Sparus aurata, and sea bass, Dicentrarchus labrax, were determined. Faecal material was collected from underneath commercial cages and subsequently transferred to a settling column. Particle settling velocity was determined using particle tracking software. Image analysis software was used to determine dimensions of selected faecal particles from which particle volume was then estimated. Faecal particles (all fish sizes) had a mean settling velocity of 0.48 cm/s (range 0.05–3.94 cm/s, n = 1021) for sea bream and 0.70 cm/s (range 0.10–6.27 cm/s, n = 1042) for sea bass. The faecal material largely consisted of very small particles and mean particle size was 0.71 mm (n = 151) and 1.12 mm (n = 150) for S. aurata and D. labrax, respectively. More than 50% of the total particle volume had a settling velocity less than 2.0 cm/s in all S. aurata size categories. In D. labrax, more than 75% of the total particle volume had settling velocities greater than 2.0 cm/s. The particle tracking DEPOMOD model was highly sensitive to different representations of these data. The predicted seabed flux of waste faecal material (g/m2/year) for D. labrax using the mean settling velocity at 0 m and 50 m from the cage was 3196 g/m2/year and 248 g/m2/year, respectively. However, when using particle settling velocity and volume distribution data, the predicted flux was over three times greater at 0 m but five times less at 50 m. For S. aurata, the predicted flux using the mean settling velocity was 3018 g/m2/year and 464 g/m2/year at 0 and 50 m, respectively. However, where distribution data were used, the values were over twice as high at 0 m and but were halved at 50 m. These results indicate that use of a single mean settling velocity value in this type of modelling does not accurately predict the extent of benthic flux. In addition, species-specific faecal settling rates should be used when modelling polyculture operations

Ontogenetic dietary changes of whitefish larvae: insights from field and experimental observations

Ontogenetic changes in resource use are widespread in many fish species. This study investigated the feeding habits of whitefish (C. lavaretus L.) larvae in Lake Annecy (France) coupled with experimental behavioral studies in order to identify the underlying mechanisms of the ontogenetic shifts in the diet. The predatory behavior of wild larvae, and the escape responses of their zooplankton prey were both videorecorded in experimental tanks under controlled laboratory conditions. Ontogenetic diet patterns showed that young whitefish larvae have a preference for small cyclops, while older larvae selectively predate cladocerans. Our experimental observations showed that the capture success rate also varied in relation to ontogenetic development in fish. Young larvae were more successful in capturing small copepods, whereas old larvae were more successful in capturing Daphnia. In addition, the larvae were able to adjust their predatory behavior (speed, pursuit) according to the swimming pattern of the prey. These observations suggest that the selective predation on cladocerans observed in old larvae is the outcome of both active and passive choices depending on the escape swimming behavior of the prey, and handling time of the predator

Oxygen consumption and ammonia excretion of the searobin Prionotus punctatus (Scorpaeniformes, Triglidae) at two different temperatures

Routine oxygen consumption and ammonia excretion were measured at 20ºC and 25ºC in the searobin Prionotus punctatus collected in Ubatuba region (22º30'S), SP, Brazil, in western South Atlantic, to investigate energy expenditure and losses through metabolic processes. IndividuaIs ranging from 1.00g to 88.47g and from 1.79g to 56.50g were used in experiments at 20ºC and 25ºC, respectively. At 20ºC and 25ºC, the averages of weight-specific oxygen consumption for the weight class of 1.00 - 10.00g, common to both temperatures, were 162.46µ 39.51 µ.10z/g/h and 200.47µ 92.46 µ.10z/g/h, respectively; for the weight class of 50.01 - 60.00g these values were 112.30 µ 22.84 µ.10z/g/h and 114.60 µ 20.36 µ.10zlg/h. At 20ºC and 25ºC, the averages of weight-specific ammonia excretion for the weight class of 1.00 to 1O.00g were 1.03 µ 0.37 fJ.M/g/h and 1.21 µ 0.65 µ.M/g/h, respectively; for the weight class of 50.01 -60.00g these values were 0.68 µ 0.13 fJ.M/g/h and 0.60 µ 0.22 µ.M/g/h. The energy budget for the species was calculated at both temperatures using the experimental data and a model for marine teleosts proposed in the literature.<br>O consumo de oxigênio de rotina e a excreção de amônia de Prionotus punctatus coletados na região de Ubatuba (22º30'S), SP, Brasil, foram medidos a 20ºC e 25ºC, para avaliar os gastos e perdas de energia com os processos metabólicos. Foram utilizados indivíduos variando de 1,00g a 88,47g e de 1,79g a 56,50g, em experimentos a 20ºC e 25ºC, respectivamente. As médias de consumo específico de oxigênio a 20ºC e 25ºC para a classe de peso de 1,00 - 10,00g, comum a ambas as temperaturas, foram 162,46µ 39,51 µ.10z/g/h e 200,47 µ 92,46 µ.10z/g/h, respectivamente; para a classe de peso de 50,01 - 60,00g esses valores foram 112,30 µ 22,84 µ.10z/g/h e 114,60 µ 20,36 µ.10z/g/h. A 20ºC e 25ºC, as médias de excreção específica de amônia para a classe de peso de 1,00 a 10,00g foram 1,03 µ 0,37 e 1,21 µ 0,65 µ.M/g/h, respectivamente; para a classe de peso de 50,01 - 60,00g esses valores foram 0,68 µ 0,13 µ.M/g/h e 0,60 µ 0,22 µ.M/g/h. O orçamento energético para a espécie foi calculado para cada temperatura utilizando-se os da.dos experimentais e modelo proposto na literatura