Determining and quantifying components of an aquaculture soundscape.

Recirculating aquaculture systems have a unique anthropogenic-based soundscape which is characterized by the type of equipment utilized, the structural configuration of walls, tanks, equipment, the substrate the tanks are situated on and even the activities of the personnel operating the facility. The soundscape of recirculation facilities is inadequately understood and remains poorly characterized, although it is generally accepted that the dominant sounds found in such facilities are within the hearing range of fish. The objective of this study was to evaluate the soundscape in a recirculating aquaculture facility from an intra-tank perspective and determine how the soundscape is shaped by a range of characteristics within the facility. Sounds were recorded across an operating aquaculture facility including different tank designs. The sounds recorded fell within previously measured pressure level ranges for recirculating systems, with the highest maximum sound pressure level (SPL) recorded at 124 dB re 1 mu Pa-2/Hz (with an FFT bin width of 46.9 Hz, centered at 187.5 Hz). The soundscape within the tanks was stratified and positively correlated with depth, the highest sound pressure occurring at the base of the tanks. Each recording of the soundscape was dominated by a frequency component of 187.5 Hz (corresponding centre of the 4th 46.9 Hz FFT analysis bin) that produced the highest observed SPL Analysis of sound recordings revealed that this peak SPL was associated with the acoustic signature of the pump. The soundscape was also evaluated for impacts of tank hood position, time of day, transient sounds and airstone particle size types, all of which were found to appreciably influence sound levels and structure within the tank environment. This study further discusses the distinctiveness of the soundscape, how it is shaped by the various operating components and considers the aquaculture soundscape in relation to natural soundscapes found within aquatic tropical environments.

Analysis of sexually dimorphic growth in captive reared cobia (Rachycentron canadum) and the occurrence of intersex individuals

The growth of three cohorts of captive reared cobia, grown in a combination of flow-though and recirculating aquaculture systems, was progressively measured to determine the existence and extent of sexually dimorphic growth in cobia. Approximately 100 fish from each cohort were individually identified and regularly weighed until the average weight of the fish was approximately 5 kg. The sex of individuals was determined through gonadal observations at the conclusion of each trial and the gender fitted retrospectively to the growth data set. Intersex gonads were observed in the first two cohorts of cobia, with 16.9% incidence in cohort 1 and 6.8% in cohort 2. Cobia is considered a gonochoristic species. This was the first reported observation of intersex gonads in cobia and the first reported occurrence of intersex gonads from a gonochoristic fish species from Australian waters. Only one fish out of the 182 examined in the third cohort was identified as intersex. There was no sexually dimorphic growth in cobia when there was a relatively high incidence of the intersex anomaly, as seen in the first two cohorts of fish. In the relative absence of the intersex condition, female cobia was significantly larger than males from 2 kg onwards. The weight of female cobia was almost 30% more than that of males at 17 months of age when average weight of the cohort was 4.6 kg. It is likely that the first two cobia cohorts were exposed to endocrine disruption in some form, and the possible sources are discussed. Statement of relevance This study demonstrated that female cobia grow significantly faster than male fish and that investigations into monosex culture could lead to significant productivity gains for cobia aquaculture. It also demonstrated that cohorts containing intersex fish did not exhibit sexually dimorphic growth. It is likely that the reproductive anomaly is the result of disruption to the endocrine system.

Assessment of Lotus (Nelumbo nucifera) in wastewater bioremediation

This project assessed the efficiency of lotus reducing the amount of nutrients that are generated in a freshwater aquaculture system. Barramundi were produced at a stocking density similar to industry practices. Lotus was grown to determine if it was capable at reducing the nutrient loading from an aquaculture system

Limb-loss in pond-reared blue swimmer crabs Portunus pelagicus (L.): Effect on growth in an indoor shedding system

Limb-loss in crustaceans can reduce moult increment and delay or advance the timing of moulting, both aspects that are likely to impact upon soft-shell crab production. Pond-reared blue swimmer crabs Portunus pelagicus were harvested and maintained in a crab shedding system. The wet weight, carapace width (CW) and the occurrence of limb-loss were assessed before stocking in the shedding system and after each of the next three moults. Many of the crabs were initially missing one or two limbs and these did not grow as much as the crabs that were intact at the start of the trial. Despite its strong correlation with wet weight, CW changes proved to be misleading. Limb-loss reduced the %CW increment but not the per cent weight increment (where the later is calculated from the actual pre-moult weight). Pre-moult weight explained much of the variation in post-moult weight, with crabs moulting to approximately double their weight. Limb-loss reduced 'growth' and production from the pond because it reduced pre-moult weight but limb-loss did not alter the weight change on shedding a given weight of crabs, although some of that change now included regeneration of limbs. One can hypothesize that much of the size variation seen in pond-reared crabs may be due to accumulated effects of repeated limb-loss, rather than genetic variation.