Tamaki Shimose

Age, growth and maturation of the blackspot snapper Lutjanus fulviflammus around Okinawa Island, Japan

The blackspot snapper Lutjanus fulviflammus is one of the most common Lutjanus species landed and consumed on Okinawa Island, Japan. Using 901 fish (29.9–304.2 mm in standard length; SL) obtained from fish markets or caught by angling, the age, growth, maturation size and maturation age were estimated. Each opaque zone formed on the otolith every year correlated with their spawning and was thought to be an annual ring. The main spawning season was estimated to be from April to July, which peaked in May and June, with a few mature fish collected in August and September. Maximum ages were observed as 24 years for both sexes and L∞ (mm SL), K and t0 (years) of the von Bertalanffy growth formula were estimated to be 276, 0.144 and −5.22 for females and 247, 0.227 and −3.18 for males, respectively. First maturation size and age were estimated to be 175 mm SL and 2 years for both sexes. A faster growth rate up to 2 years will allow reproduction at a young age and provide many chances for spawning throughout their long life. Furthermore, the possibility exists that populations would easily recover if regulations were established.

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis (Perciformes: Latidae) around Okinawa Island, Japan

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis were studied using 291 specimens obtained around Okinawa Island, Japan. Otolith opaque zones that formed every year correlated with spawning activity and were thought to be annual rings. Growth of this species was rapid during the first 2 years, reaching 186.2–270.3 mm in standard length (SL). Females (196.6–334.0 mm SL) were larger than males (186.2–288.6 mm SL), caused by differential growth between sexes, which started before 2 years of age. Most of the specimens were 1–11 years old and accounted for 96% in total. Spawning season was estimated to be from April to October by gonadosomatic index (GSI) and histological observation. The smallest mature female and male were 217.0 mm SL (2 years) and 206.0 mm SL (2 years), respectively. After recruitment in rocky areas up to about 200.0 mm SL and 2 years of age, Psammoperca waigiensis were then found to soon mature.

Seasonal occurrence and feeding habits of black marlin, Istiompax indica, around Yonaguni Island, southwestern Japan

The seasonal occurrence of black marlin, Istiompax indica, around Yonaguni Island, southwestern Japan, was analyzed. Black marlin was abundant from April to July, and the majority of landed fish were female (97%). None of these females was reproductively mature. The condition factor of females increased from April to July. Of 56 black marlin examined, 21 individuals contained 12 prey species; the most important prey species was skipjack tuna, Katsuwonus pelamis, and one neonatal silky shark, Carcharhinus falciformis, was also found. These results indicate that the occurrence of black marlin off Yonaguni Island was associated with feeding and not with spawning.

Evidence for use of the bill by blue marlin, Makaira nigricans, during feeding

The function of the rostrum (bill) in istiophorid billfi shes has been theorized and discussed for some time (Wisner, 1958; Rivas, 1975; Nakamura, 1983; Frazier et al., 1994). Billfi shes have been reported to use their bill for striking (Voss, 1953; Baker, 1966; Nakamura, 1983) or spearing prey items (van der Elst and Roxburgh, 1981), and possible use it in defense from large predators (Fierstine, 1997). However, the use of the bill in feeding behavior may not be a necessity, based on observations of healthy billfi sh without bills and/ or marlins, which do not use their bills when pursuing a trolled bait (Rivas, 1975). In this study, the possibility that blue marlin, Makaira nigricans, use their bill to attack prey is examined through observations on the condition of prey items found among stomach contents. Stomach samples were collected from blue marlin caught by the surface troll bait fi shery and landed at Yonaguni Island during February 2003 to February 2006 (sampling details are described in Shimose et al., 2006). Lower jawfork length (LJFL) was recorded to the nearest centimeter (cm) for all blue marlin measured. A total of 339 undigested prey items were obtained from 227 blue marlin over a size range of 169–324 cm LJFL. Mantle length for squid prey and standard length (SL) for fi sh prey were recorded to the nearest millimeter (mm). Observations were also recorded on the presence of any external injuries on prey items that were examined in this study. Striking behavior could not be recognized from the stomach contents because this behavior gives few injuries on a prey body. Spearing situations.—A total of 130 prey items (38% of total) were observed to have injuries attributed to spearing/slashing by the bill; these injuries were categorized into three types. Spearing injuries to the body were observed in 14 prey items (11% of injured prey, Fig. 1A). Slashing injuries to the dorsal, ventral, and caudal portions were observed in 105 prey items (81% of injured prey, Fig. 1B). Ichthyol Res (2007) 54: 420–422 DOI 10.1007/s10228-007-0419-x News and Comments

Interspecific differences in prey items in relation to morphological characteristics among four lutjanid species (Lutjanus decussatus, L. fulviflamma, L. fulvus and L. gibbus)

Clarifying interspecific differences in prey items in relation to morphological characteristics is a fundamental aspect to understand the mechanism enabling the diversity of feeding ecology of fishes. The aim of the present study was to clarify the relationship between prey items and body shape variation, teeth and mandible characteristics for four lutjanid species: Lutjanus decussatus, L. fulviflamma, L. fulvus and L. gibbus. Stomach contents analysis revealed that the main prey items of L. decussatus were fishes, L. fulviflamma were crabs and fishes, and L. fulvus and L. gibbus was crabs. Body shape analysis revealed that L. decussatus and L. fulviflamma had a shallower body depth whereas L. fulvus and L. gibbus had a deeper body depth. The two species with a shallower body had long teeth whereas the other two species with a deeper body depth had shorter teeth. The jaw-lever mechanics were compared and L. decussatus and L. fulviflamma have a faster mouth opening–closing mechanism. Canonical correspondence analysis revealed that fishes was the major prey item for the species having a shallower body depth, higher teeth length and lower ratios of in-lever to out-lever of mandibles, whereas crabs was the major prey item for the species having a deeper body depth, lower teeth length and higher ratios of in-lever to out-lever of mandibles. It is suggested that the interspecific differences in main prey items among the four species are directly related to behavioral differences based on body shape, teeth characteristics and jaw-lever mechanics.

Quantitative Analysis of Distribution of Lutjanus Fishes (Perciformes: Lutjanidae) by Market Surveys in the Ryukyu Islands, Okinawa, Japan

Abstract: Distribution patterns of Lutjanus fishes (Perciformes: Lutjanidae) in the Ryukyu Islands, Okinawa, Japan, were quantitatively investigated by fish market surveys in Okinawa Island (26° N, 127° E) and Ishigaki Island (24° N, 124° E). At Okinawa and Ishigaki, totals of 296 and 326 ports × days surveys recorded 8,866 and 8,246 individual Lutjanus fishes, respectively, of 19 species. Frequency of occurrence and number landed for some commercial Lutjanus species were different between the two islands during comparison within the same gear type. Five species (e.g., L. fulviflammus, L. gibbus) that were common (>1.0% in frequency of occurrence) at both islands were thought to have main distribution from south of the Ryukyu Islands to around Okinawa Island. Two species (L. decussatus, L. rivulatus) that were common at Ishigaki and not at Okinawa were thought to have main distribution from south of the Ryukyu Islands to around Ishigaki Island. Three species (e.g., L. bengalensis, L. stellatus) that were not common at both islands were thought to have main distribution outside the Ryukyu Islands. The remaining five species (e.g., L. malabaricus, L. vitta) were common at Okinawa but not at Ishigaki, despite the fact they are widely distributed in the area south of the Ryukyu Islands. This distribution pattern looks discontinuous and implies that the environments around Ishigaki Island are not preferable for nursery grounds or adult habitats of these species. Both qualitative (only presence or absence) and quantitative descriptions of the distribution will facilitate understanding of their biogeography.

Life history of an invasive and unexploited population of Nile tilapia (Oreochromis niloticus) and geographical variation across its native and non-native ranges

Although the life history traits of Nile tilapia, Oreochromis niloticus have been studied since the early 20th century, the potential range of life history parameters in unexploited populations and geographical variability in life history traits are still poorly understood. We explored life history traits (age composition, growth rate, mortality, size, and age at maturity) of an invasive and unexploited population in the Tabaru River, Yonaguni-jima Island, southwestern Japan, through comparisons with exploited populations across the species’ global distribution. Analysis of sectioned otoliths from 307 fish revealed that growth and maximum age were sexually dimorphic (females growing less but having greater longevity). Large-scale comparisons with exploited populations revealed that the unexploited Tabaru River population had a greater life span than exploited populations in other regions, but the growth rate was in the middle of the range of observed values. Although a high variation in life history parameters was observed among populations (L∞, K, maximum age), we found no significant variation in life history traits by latitude or between African and non-African populations. Such a combination of long life span and high variability in life history traits in response to environmental and fishing pressures may aid the success of non-native Nile tilapia in various environments.

Age determination and growth estimation from otolith micro-increments and fin spine sections of blue marlin (Makaira nigricans) in the western North Pacific

Age determination and growth estimation of blue marlin (Makaira nigricans) were performed by combining method of otolith micro-increment counts of 27 young (17–185-cm lower jaw–fork length, LJFL) and sectioned dorsal fin spines of 571 adult individuals (155–352cm). Otolith micro-increments were counted with ages of 26–338 days old. The estimated mean length (185cm) at Year 1 and growth rate were used to predict the position of the first annual growth band in sectioned fin spines. Distinct growth bands were formed in fin spines annually between September and October. Indistinct growth bands were considered false-annual growth bands. The observed and back-calculated LJFLs at each age were highly variable for both sexes. Von Bertalanffy growth parameters were estimated using mean back-calculated LJFL data as: L∞=295cm, k=0.23, t0=–3.31 years for females and 212cm, 0.29, –4.49 years for males. Females grew to >200cm in 2 years and to >250cm in 5 years on average, whereas the growth of males slowed appreciably after they reached the age of 1 year. This is the first study of blue marlin growth for entire life stages.