Effect of incubation temperature on muscle growth of barramundi Lates calcarifer at hatch and post-exogenous feeding.

Muscle morphology was investigated in newly hatched barramundi Lates calcarifer larvae incubated at set temperatures (26, 29 and 31 degrees C) prior to hatching. Three days after hatching (the start of exogenous feeding), larvae from the 26 and 31 degrees C treatments were each divided into two groups and reared at that temperature or transferred over the period of several hours to 29 degrees C (control temperature). Incubation temperature significantly affected muscle cellularity in the developing embryo, with larvae incubated at 26 degrees C (mean +/-s.e. 223.3 +/- 7.9) having on average 14.4% more inner muscle fibres than those incubated at 31 degrees C (195.2 +/- 8.8) and 4.8% more than those incubated at 29 degrees C (213.5 +/- 4.7). Conversely, inner muscle fibre cross-sectional area significantly increased at the warm incubation temperature in L. calcarifer, so that the total cross-sectional muscle area was not different between treatment groups. The total cross-sectional area of superficial muscle fibres and the proportion of superficial to total fibre cross-sectional area in just hatched L. calcarifer were also affected by incubation temperature, with incubation at the cool temperature (26 degrees C) increasing both the total cross-sectional area and proportion of superficial muscle fibres. By 9 days post-hatch, the aforementioned differences were no longer significant. Similarly, there was no difference in total superficial fibre cross-sectional area between any treatment groups of L. calcarifer, whereas incubation temperature still significantly affected the proportion of superficial to total muscle fibre cross-sectional area. Larvae hatched and grown at 31 degrees C had a significantly reduced percentage of superficial muscle cross-sectional area (mean +/-s.e. 5.11 +/- 0.66%) compared with those incubated and grown at 29 degrees C (8.04 +/- 0.77%) and 26 degrees C (9.32 +/- 0.56%) and those incubated at 26 degrees C and transferred to 29 degrees C (7.52 +/- 0.53%), and incubated at 31 degrees C and transferred to 29 degrees C (6.28 +/- 0.69%). These results indicate that changes in muscle cellularity induced by raising or lowering the incubation temperature of L. calcarifer display varying degrees of persistence over developmental time. The significance of these findings to the culture of L. calcarifer is discussed.

Mechanisms of electron acceptor utilization: implications for simulating anaerobic biodegradation.

Simulation of biodegradation reactions within a reactive transport framework requires information on mechanisms of terminal electron acceptor processes (TEAPs). In initial modeling efforts, TEAPs were approximated as occurring sequentially, with the highest energy-yielding electron acceptors (e.g. oxygen) consumed before those that yield less energy (e.g., sulfate). Within this framework in a steady state plume, sequential electron acceptor utilization would theoretically produce methane at an organic-rich source and Fe(II) further downgradient, resulting in a limited zone of Fe(II) and methane overlap. However, contaminant plumes often display much more extensive zones of overlapping Fe(II) and methane. The extensive overlap could be caused by several abiotic and biotic processes including vertical mixing of byproducts in long-screened monitoring wells, adsorption of Fe(II) onto aquifer solids, or microscale heterogeneity in Fe(III) concentrations. Alternatively, the overlap could be due to simultaneous utilization of terminal electron acceptors. Because biodegradation rates are controlled by TEAPs, evaluating the mechanisms of electron acceptor utilization is critical for improving prediction of contaminant mass losses due to biodegradation. Using BioRedox-MT3DMS, a three-dimensional, multi-species reactive transport code, we simulated the current configurations of a BTEX plume and TEAP zones at a petroleum-contaminated field site in Wisconsin. Simulation results suggest that BTEX mass loss due to biodegradation is greatest under oxygen-reducing conditions, with smaller but similar contributions to mass loss from biodegradation under Fe(III)-reducing, sulfate-reducing, and methanogenic conditions. Results of sensitivity calculations document that BTEX losses due to biodegradation are most sensitive to the age of the plume, while the shape of the BTEX plume is most sensitive to effective porosity and rate constants for biodegradation under Fe(III)-reducing and methanogenic conditions. Using this transport model, we had limited success in simulating overlap of redox products using reasonable ranges of parameters within a strictly sequential electron acceptor utilization framework. Simulation results indicate that overlap of redox products cannot be accurately simulated using the constructed model, suggesting either that Fe(III) reduction and methanogenesis are occurring simultaneously in the source area, or that heterogeneities in Fe(III) concentration and/or mineral type cause the observed overlap. Additional field, experimental, and modeling studies will be needed to address these questions.