Investigation on the contribution of swim bladder to hearing in crucian carp (Carassius carassius).

The swim bladder in some teleost fish functions to transfer the sound energy of acoustic stimuli to the inner ears. This study uses the auditory evoked potential tests, micro-computed tomography scanning, reconstruction, and numerical modeling to assess the contribution of the swim bladder to hearing in crucian carp (Carassius carassius). The auditory evoked potential results show that, at the tested frequency range, the audiogram of fish with an intact swim bladder linearly increases, ranging from 100 to 600 Hz. Over this frequency, the sound pressure thresholds have a local lowest value at 800 Hz. The mean auditory threshold of fish with an intact swim bladder is lower than that of fish with a deflated swim bladder by 0.8-20.7 dB. Furthermore, numerical simulations show that the received pressure of the intact swim bladders occurs at a mean peak frequency of 826 ± 13.6 Hz, and no peak response is found in the deflated swim bladders. The increased sensitivity of reception in sound pressure and acceleration are 34.4 dB re 1 µPa and 40.3 dB re 1 m·s-2 at the natural frequency of swim bladder, respectively. Both electrophysiological measurement and numerical simulation results show that the swim bladder can potentially extend hearing bandwidth and further enhance auditory sensitivity in C. carassius.

Call properties of the large yellow croaker (Larimichthys crocea) during reproduction with insight into directivity.

The investigation of the large yellow croaker (Larimichthys crocea) deserves more attention due to its high commercial value as an important aquaculture fish species. This study was initiated by deploying a passive acoustic monitoring device to record the calls from the L. crocea during the spawning process in an aquaculture facility. The subsequent analysis suggested the croakers produced at least two types of calls with considerable energy distributed up to 1000 Hz. The acoustic data and the computed tomography scanning of an adult croaker were used to develop a numerical model to address the directivity of the calls at frequencies up to 1000 Hz. The radiation patterns at all frequencies were assigned with respective weights and then combined to estimate an overall acoustic radiation pattern for both types of the calls. The backward transmission was greater for both types of calls by 1.85 dB on average. The reduction of size by 20% in the swim bladder resulted in a stronger sidelobe in the frontal direction, indicating its influence on call directivity. These results provided information on the directivity of the croaker calls and understanding of fish acoustics.

Marinicella rhabdoformis sp. nov., isolated from coastal sediment.

A Gram-stain-negative, rod-shaped, facultative anaerobic bacterium, designated strain 3539T, was isolated from coastal sediment of Weihai, PR China. Optimal growth occurred at 28 °C, pH 7.5-8.0 and in the presence of 3.0 % (w/v) NaCl. Results of phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 3539T formed a robust clade with members of the genus Marinicella and was closely related to Marinicella litoralis JCM 16154T, Marinicella sediminis F2T and Marinicella pacifica sw153T with 97.7, 96.2 and 95.4 % sequence similarity, respectively. The average amino acid identity, percentage of conserved proteins, average nucleotide identity and digital DNA-DNA hybridization values between strain 3539T and M. litoralis JCM 16154T were 64.9, 68.3, 72.8 and 18.9 %, respectively. The genomic DNA G+C content of strain 3539T was 42.0 mol%. The dominant respiratory quinone was ubiquinone-8, and the major fatty acids were iso-C15 : 0 and summed feature 3 (C16 : 1 ω7c/C16 : 1 ω6c). The polar lipids of strain 3539T consisted of phosphatidyldimethylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, one unidentified aminophospholipid, one unidentified lipid and three unidentified phospholipids. Based on the combination of phylogenetic, phenotypic and chemotaxonomic data, strain 3539T is considered to represent a novel species within the genus Marinicella in he family Alcanivoracaceae, for which the name Marinicella rhabdoformis sp. nov. is proposed. The type strain of the new species is 3539T (=KCTC 72414T=MCCC 1H00388T).