Effects of density, starvation and size difference on aggressive behaviour in juvenile yellowtails (Seriola quinquevadiata)

The effects of density, starvation and size difference on aggressive behaviour in juvenile yellowtails, Seriola quinqueradiata (Temminck and Schlegel), wee investigated. When fish were acclimated to densities of 1, 2, 4, 8, and 16 fish L-1, the frequency of aggressive behaviour per fish decreased significantly. Following starvation for 0, 4, 8, 12 and 24 h, the highest aggression was observed at 24 h, while levels of aggression were equal between 0 and 8 h. According to a pair match test from one batch among three groups of different size (total length mm: 16.6 ± 2.0, 21.1 ± 4.9), the highest aggression was observed in the group with the largest size difference. therefore, in view of the three parameters investigated, aggressive behaviour in the yellowtail was concluded to be positively starvation- and size-dependent, but negatively density-dependent. Synthesizing all relevant results, including abiotic factors such as the light condition, a practical method is presented to reduce mortality caused by aggressive behaviour in yellowtail cultures

Age, Growth, and Sexual Development in the Self-fertilizing Hermaphroditic Fish Rivulus marmoratus

We studied age, growth, and sexual development in the early life intervals of the self-fertilizing mangrove killifish, Rivulus marmoratus. Newly hatched (day 0) individuals had sagittal otoliths of 60 μm radius, with about 30 increments. Sequential sampling until about day 60 after hatching yielded otoliths with the number of increments outside the 60 μm radius equal to the daily age of the fish. Alizarin complexone marking of otoliths also confirmed the increments were daily, and demonstrated the applicability of this technique to field studies for capture-mark-recapture, or age and growth estimates. Individuals fed a restricted amount of food formed fewer daily otolith growth increments than fish fed to satiation each day. Using histological analysis for identifying gonad morphogenesis, we found no correlation between gonadal development and external appearance (caudal ocellus, orange fin colouration) in young fish of known ages. The caudal ocellus was not present until 9 mm total length, and developed thereafter. Of 136 individuals examined, fish less than 17.2 mm total length (TL, n = 124) were females. Testicular tissue first appeared among individuals 17-18 mm TL (n = 3), while some individuals greater than 18 mm TL (n = 8) were functional hermaphrodites. The single male in our study was relatively of small body size (9.6 mm, day 37) with a distinct caudal ocellus, indicating that it is presumably a primary male

Improvement of the survival in the seven-band grouper Epinephelus septemfasciatus larvae by optimizing aeration and water inlet in the mass-scale rearing tank

The water flow in larval rearing tanks has been indicated to cause mass mortality of the seven-band grouper Epinephelus septemfasciatus larvae. Therefore, a new aerating method was tested in an actual scale intensive rearing tank (8.0 m in diameter, 1.87 m of water depth, 100 m3 of volume), in which an aerator was positioned at the center of the rearing tank surrounding cylindrical drain (1.2 m in diameter) to generate the flow field, and seven larval rearing trials were performed. The survival rate with the former aeration methods were compared, in which several aerators were located in the rearing tank. The survival rate at 10 days after hatching with the new aeration method (61.5 ± 5.1%, n = 7) was approximately three times higher than the former methods (21.2 ± 13.7%, n = 6). The flow environment of rearing tanks was also examined by quantifying the flow field, and the relationship between the flow field in the rearing tank, behavior of larvae and survival discussed. It was confirmed that the vertical circulating flow was observed in rearing tanks, and determined effectively the survival and the behavior of grouper larvae in patchiness

Early development of the self-fertilizing mangrove killifish Rivulus marmoratus reared in the laboratory

The mangrove killifish Rivulus marmoratus was reared at 25° ± 1°C and 17 ppt salinity from 0 to 100 days after hatching (DAH), and its early development was described by examining growth and morphometric parameters, meristic characters (vertebral and fin-ray counts), bone-cartilage development, and pigmentation. Growth was isometric for preanal length, head length, snout length, body depth, pectoral-fin length, dorsal-fin length, anal-fin length, and caudal-peduncle depth. Negative allometric growth was observed in eye diameter and gape size. Meristic counts (mean ± SD) for vertebrae (34.2 ± 0.4) and dorsal- (8.6 ± 0.5). anal- (11.4 ± 0.5). and caudal-fin rays (30.2 ± 0.8) were complete at 0 DAH (n = 5). whereas pectoral-fin rays and pelvic-fin rays were complete by 30 DAH (14.5 ± 0.4. n = 5) and 60 DAH (4.2 ± 0.8. n = 5). Full ossification of meristic elements proceeded in the following sequence: vertebrae (by 30 DAH), caudal-, dorsal-, and anal-fin rays (by 60 DAH), pectoral-fin rays (between 60 DAH and 100 DAH), and pelvic-fin rays (by 100 DAH). Both morphological characters and meristic counts indicate that this species can be considered to be a juvenile after 9.8 mm in standard length (20 DAH)

Isolation of mixis-related genes from the rotifer Brachionus plicatilis using subtractive hybridization

The monogonont rotifer Brachionus plicatilis produces resting eggs through sexual reproduction (mixis), which is affected by external and internal factors. We collected resting eggs from rotifers cultured at 15 and 25°C and hatched them with and without 14-day dormancy in the dark. Stem females hatched from both conditions were further cultured at 15, 20 and 25°C. We obtained two phenotypes, one with high mixis (more than 50%), which was hatched from resting eggs formed at 15°C without dormancy, and another in which sexual reproduction occurred at 25°C and resting eggs were formed at 15°C with a 14-day dormancy. In the latter phenotype, mictic females appeared at 15°C, but not at 25°C. Using subtractive hybridization, we isolated one gene from the latter phenotype of females that had no significant similarity to known genes in BLAST searches. We propose that this gene is unique to rotifer mictic reproduction. Ongoing characterization of this gene attempts understand its role in mixis.The original publication is available at www.springerlink.co

Administration of tetrodotoxin protects artificially raised juvenile tiger puffer Takifugu rubripes from predators

We examined the effects of tetrodotoxin (TTX) administration on artificially raised tiger puffer Takifugu rubripes juvenile survival after release into a mesocosm with predators to clarify the ecological significance of TTX. Pellets containing three different concentrations of TTX [0 as the control, 7 and 14 mouse units (MU)/g diet] were fed to non-toxic artificially raised T. rubripes juveniles for 10 days. TTX accumulation in the various tissues of fish was detected except for in the control diet group. TTX administration did not affect survival or growth of the fish. One hundred fish from each diet group were released together after TTX administration into a salt pond mesocosm (2650 m2) with predators (Lateolabrax sp.) for 5 days. Survival after release was significantly higher in both the fish fed with the 7 MU TTX/g diet (62%) and the 14 MU TTX/g diet (74%) than in the control fish (32%)

Larval fish behavior can be a predictable indicator for the quality of Japanese flounder seedlings for release

In the Japanese flounder (Paralichthys olivaceus), a typical shivering behavior in the metamorphosing larvae called the Ω (Ohm)-posture is often observed; it disappears after the transition from the larval to juvenile stage, coinciding with the onset of aggressive behavior. From previous studies, I hypothesized that there is a positive correlation between the Ω-posture and aggressive behavior. A rearing experiment using individual otolith markings by ALC (Alizarin complexone) was conducted. On day 21 after hatching (metamorphosing stage), 200 fish showing Ω-posture (Ω fish) were labeled with ALC and another 200 fish (non-Ω fish) were not labeled before being transferred into the same tank and reared until day 58 (juvenile stage). Reverse sets of 200 otolith-labeled non-Ω fish and 200 otolith-unlabeled Ω fish were reared in the same manner. From behavioral observation of a total of 100 juveniles, I found a social rank with three categories: dominants, intermediates and subordinates, with the body sizes of the former being the largest. There was a positive correlation between Ω-posture and aggressive behavior as was revealed by checking the otolith label. Therefore, the Ω-posture is defined as a precursor behavior of aggression in the metamorphosing stage, indicating that we can predict the aggression of juveniles in this species by their behavior in the metamorphosing stage

Onset and development of aggressive behavior in the early life stages of the seven-band grouper Epinephelus septemfasciatus

Onset and development of aggressive behavior were observed in the early life stages of seven-band grouper Epinephelus septemfasciatus. Fish culture was divided into two terms: the first term, from hatch until 21 days after hatching (DAH); and the second term, from 21 DAH until settlement (65 DAH). During the second term the effect of different aeration rate on survival was investigated. Survival during the first term was 14.1 ± 7.1%. In the second term, survival in control tanks (aeration rate 200 mL/min) was 14.7 ± 10.2% and 18.8 ± 7.8% in the increasing aeration tanks (aeration rate 200-800 mL/min). Behavioral observations were conducted at about 8-day intervals and aggressive behavior was quantified by the frequency of chase behavior. Aggressive behavior was first observed on 52 DAH when pigment appeared on the dorsal area of the metamorphosing larvae (standard length 16.6 ± 6.0 mm). Aggressive behavior significantly increased from 59 DAH coinciding with the beginning of settlement

Whole-Body Cortisol Concentrations and Ontogeny of Aggressive Behavior in Yellowtail (Seriola quinqueradiataTemminck & Schlegel; Carangidae)

Ontogenetic changes in whole-body immunoreactive cortisol concentrations (IRC) and aggressive behavior were examined in yellowtailSeriola quinqueradiata(Temminck & Schlegel; Carangidae). Baseline IRC significantly increased during the transition from larval to juvenile stage and was correlated with the onset of aggressive behavior. Handled fish (13.1 ± 2.6 ng/g tissue) showed an IRC level about three times higher than unhandled fish (4.7 ± 1.4 ng/g tissue), indicating that whole-body immunoreactive cortisol level may be an indicator of stress in juvenile yellowtails. Behaviorally subordinate fish (8.6 ± 1.6 ng/g tissue,n = 4) showed IRC levels significantly higher than dominant fish (0.6 ± 0.3 ng/g tissue, n = 4). Whole-body immunoreactive cortisol levels may thus reflect stress and social status in juvenile yellowtails, and the inverse relationship between social rank and IRC may result from agonistic interactions