Estuarine fishes in two large eastern Australian coastal rivers—does prawn trawling influence fish community structure?

Fish communities were sampled quarterly over a 2-year period at sites along the estuarine gradient of two large coastal rivers, the Richmond and Clarence, located in eastern Australian (NSW). A total of 175 582 fish from 73 species was captured, with two species making up 65% of this total. Many fish species of economic importance in local coastal waters were captured, predominantly as juveniles. Multivariate analysis revealed three significantly different groupings of sites corresponding to the marine, brackish and tidal-freshwater zones of the two rivers. The two rivers were remarkably similar in terms of overall abundance and diversity of fish, and structuring of fish communities, despite a large-scale and intensive prawn trawling industry operating on the Clarence River. Dependency of fishes on estuarine habitats and the distribution of some of the dominant fish species in relation to estuarine gradients are discussed.     

Can we adjust a marine cyclopoid copepod to freshwater?—First step towards a ‘universal’ live feed product for fish and shrimp larvae

The copepod Apocyclops royi tolerates very low salinity while being highly capable of synthesizing n-3 fatty acids based on PUFA-poor diets. The feasibility of culturing A. royi in freshwater fed with baker's yeast was evaluated. The copepods were adjusted for 8 days by decreasing stepwise from salinity 20 to freshwater diluting with deionized water. Initially, the cultures exhibited adequate survival and reproduction. However, after 10 days in freshwater, they stopped reproducing presumably due to the lack of vital ions in the medium. Therefore, before continuing the freshwater cultures, we tested the survival of a batch of salinity 1 pre-acclimated adults and copepodites in various types of freshwater: deionized, bottled ‘mineral’ and tap water for 48 h. All copepods died in deionized water, but a significantly higher survival, 29% ± 11%, was found in mineral water versus 11% ± 8% in tap water. Hence, we continued culturing the copepods in freshwater using ‘Maglekilde spring’ water as diluter. The copepods regained and kept reproducing until day 71 where the experiment was terminated. After a 48 h freshwater versus salinity 20 exposure, nauplii survival was significantly less in freshwater 25 ± 12 versus 79 ± 20 (±STD) at salinity 20 but not different in mean body length. For the first time, we conducted NMR metabolomics revealing a large decrease in glycine betaine and a large increase in lactate in the copepods when challenged by freshwater versus salinity 20. There is obviously a ‘price to pay’ when culturing not only the copepods in freshwater, but also perspectives in developing a ‘universal’ A. royi live-feed product.     

The ‘killer shrimp’ Dikerogammarus villosus (Crustacea,Amphipoda) invading Alpine lakes: overland transport by recreational boats and scuba‐diving gear as potential entry vectors?

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Do network relationships matter? Comparing network and instream habitat variables to explain densities of juvenile coho salmon (Oncorhynchus kisutch) in mid‐coastal Oregon,USA

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An analysis of the effect of diet and genotype on protein and energy utilization by the black tiger shrimp,Penaeus monodon – why do genetically selected shrimp grow faster?

Selected (G8) and wild‐type (W) genotypes of black tiger shrimp (Penaeus monodon) juveniles (initial weight G8 = 9.14 ± 0.36 g per animal and W = 8.44 ± 0.10 g per animal) were fed either of two diet types in a clear‐water tank trial to examine the effects of diet type and genetics on growth and feed utilization parameters. Animals were fed twice daily at one of the five ration levels from starvation to apparent satiety. All uneaten feed was accounted for and moults removed. Starved animals were measured after 3 weeks; those fed were measured at both three and 6 weeks. Diet type varied by protein content, raw material choice and the presence [high‐specification diet (HSD)] or absence [low‐specification diet (LSD)] of bioactive substances. At the end of the study, faecal samples were also collected to determine the digestible protein and energy content of each diet by each genotype. Whole animal protein and energy content were also assessed from samples from the initial populations and those from each tank. Growth after 6 weeks of those animals fed to satiety showed that the G8 animals fed the HSD diet had grown at a rate of 2.56 g week^?1, significantly faster than any other treatment. Those G8 animals fed the LSD diet (1.81 g week^?1) had grown significantly faster than the W animals fed the HSD diet (1.25 g week^?1), while those W animals fed the LSD diet (0.61 g week^?1) grew the slowest. Using the data from the varying ration levels, we were able to define that the growth gains of the G8 animals were achieved not only by a greater appetite, but also through lower maintenance energy costs (29 versus 57 kJ kg^?0.8 day^?1) and a more efficient energy conversion (19.5% versus 11.6% when fed the HSD diet). Use of a low‐specification diet with the G8 and W shrimps limited their growth and impaired their potential as demonstrated by a curvilinear response of growth to intake. By comparison, those shrimp fed the HSD diet had a relatively linear growth response to intake.     

Adapting bioenergetic factorial modelling to understand the implications of heat stress on barramundi (Lates calcarifer) growth,feed utilisation and optimal protein and energy requirements – potential strategies for dealing with climate change?

The implications of temperature on bioenergetics for barramundi (Lates calcarifer) were defined in an improved factorial model that encompassed revised parameters accounting for effects over the temperature range of 16–39 °C and size range of 10–3000 g. A revised growth function describing weight gain by barramundi as a function of fish weight and temperature was derived from farm and laboratory data and included a term for a shift in optimal temperature with fish size: Gain (g fish^?1 day^?1) = (K + xT + yT ² + zT³) * (weight)^ax+b. Maintenance energy and protein demand functions were also derived on a similar form, and all three functions combined to form the basis of a factorial model for energy and protein demand. Using this model, optimal iterative feed specifications were defined for a range of fish sizes at temperatures of 25, 30 and 35 °C. A feed demand model was also developed based on the demand for digestible energy (DE) at each of these temperatures. The model shows that at high temperatures (35 °C), there is an increase in digestible protein (DP) to DE demand, and that with increasing size, there is a decrease in the DP to DE demand.