Clifford L. W. Jones

Profiling bacterial communities associated with sediment-based aquaculture bioremediation systems under contrasting redox regimes

Deposit-feeding invertebrates are proposed bioremediators in microbial-driven sediment-based aquaculture effluent treatment systems. We elucidate the role of the sediment reduction-oxidation (redox) regime in structuring benthic bacterial communities, having direct implications for bioremediation potential and deposit-feeder nutrition. The sea cucumber Holothuria scabra was cultured on sediments under contrasting redox regimes; fully oxygenated (oxic) and redox stratified (oxic-anoxic). Taxonomically, metabolically and functionally distinct bacterial communities developed between the redox treatments with the oxic treatment supporting the greater diversity; redox regime and dissolved oxygen levels were the main environmental drivers. Oxic sediments were colonised by nitrifying bacteria with the potential to remediate nitrogenous wastes. Percolation of oxygenated water prevented the proliferation of anaerobic sulphate-reducing bacteria, which were prevalent in the oxic-anoxic sediments. At the predictive functional level, bacteria within the oxic treatment were enriched with genes associated with xenobiotics metabolism. Oxic sediments showed the greater bioremediation potential; however, the oxic-anoxic sediments supported a greater sea cucumber biomass. Overall, the results indicate that bacterial communities present in fully oxic sediments may enhance the metabolic capacity and bioremediation potential of deposit-feeder microbial systems. This study highlights the benefits of incorporating deposit-feeding invertebrates into effluent treatment systems, particularly when the sediment is oxygenated.

Filial Cannibalism in the Swordtail Xiphophorus Helleri (Poeciliidae)

To understand behaviour during filial cannibalism in swordtails (Xiphophorus helleri), the parturition behaviour of eight individually kept females was recorded on videotape. Three levels of female activity (low, medium and high) were quantified by measuring the duration of each. Four additional behavioural events (non-cannibalistic feeding, as well as the birth, attack and cannibalism of juveniles) were quantified by determining the frequency of each. Females gave birth most frequently at a low level of activity and at this level of activity they most often gave birth at the top of the tank. Of all the attacks by females on the young, 84.4% occurred in the light. Most attacks were recorded at the bottom of the tank and 84.0% of all cannibalism occurred at the bottom. Cannibalism was most successful at the bottom of the tank with a cannibalism:attack ratio of 1:2.2 and least successful in the middle where no cannibalism was recorded. In the light, females spent more time at the top of the tank, whereas in the dark they spent more time at the bottom. It was suggested that the rate of cannibalism might be reduced if parts of the tank were kept constantly dark and if females were restricted from reaching those areas in the tank where the frequency of cannibalism was highest, namely the top and the bottom of the tank. Experimental designs and working hypotheses for future studies are discussed.

THE EFFECT OF DIETARY PROTEIN LEVEL ON TOTAL AMMONIA NITROGEN AND FREE AMMONIA NITROGEN CONCENTRATIONS IN A SERIAL-USE RACEWAY USED TO FARM SOUTH AFRICAN ABALONE, HALIOTIS MIDAE LINNAEUS, 1758

ABSTRACT Ammonia is a toxic metabolite of protein catabolism that can limit growth and health of aquatic animals. This study investigated the effect of dietary protein level on the average total ammonia (TAN) and free ammonia nitrogen (FAN) concentrations in a serial-use raceway used to farm South African abalone, Haliotis midae Linneaus. Three isoenergetic diets contained 33% (P33), 26% (P26), and 22% (P22) protein. Biomass of abalone was 7.6 ± 0.1 kg/300-L tank (45–55 g/abalone). TAN and FAN concentrations were significantly correlated with dietary protein (P) (P < 0.0001) and flow index (FI; as measured by liters per hour per kilogram; P < 0.0001), and could be estimated using the models TAN = 9.73 P – 110.3 log (FI), and FAN = 0.132 P – 1.10 log (FI). Mean FAN concentration in the P22 and P26 treatments was 67% and 41% lower, respectively, than in tanks fed the P33 diet. Because this species can grow well on low-protein diets, it is hypothesized that a reduction in percentage protein will improve the carrying capacity of serial-use systems. The models estimate to what extent discharge of nitrogen could be reduced through lowering the protein level in the formulated diet.

The Effect of Juvenile Abalone Haliotis midae (Linnaeus, 1758) Weaning Diet on Gut-Bacterial Formation

ABSTRACT Previous research has shown that gut-bacterial populations in farmed abalone are shaped by ontogeny, their macroalgal diet substrates, bacteria present in the environment, and other environmental factors. It has been suggested that weaning postsettlement diatom-fed abalone onto artificial feed may alter the natural succession of bacterial establishment in their guts. The gut-bacterial composition of Haliotis midae (5–9 mm) weaned onto either a commercial formulated feed (Abfeed-S34), fresh kelp (Ecklonia maxima), or a commercial formulated feed containing kelp (E. maxima) (Abfeed-S34K) was compared. The gut microbiota of postsettlement diatom-fed abalone was dominated by Planctomycetes. Weaning to kelp or formulated feed resulted in a significant difference in the gut-bacterial communities, with the Firmicutes becoming dominant in the kelp-fed treatment and the Proteobacteria dominating in the two formulated feed treatments (analysis of similarities: R = 0.77, P = 0.02). The gut microbiota of kelp-fed abalone displayed a relatively low diversity compared with that of abalone fed formulated feeds and was dominated by fermentative Clostridia bacteria. There was no difference in gut-bacterial communities of the abalone fed commercial formulated feed with or without kelp inclusion. The dominance of the Clostridia in the kelp-fed abalone guts is explained by the large volume of fermentable polysaccharides present in macroalgae, whereas the energy-rich formulated feeds appeared to reduce the selectivity of the gut environment resulting in a relatively higher bacterial diversity.