Ecology and life history of penaeid shrimps

Fourteen species of penaeid shrimps with commercial value in Batan Bay and Tigbauan-Guimbal waters were identified as follows: Penaeus monodon, P.semisulcatus, P.japonicus, Metapenaeus ensis, M.burkenroadi, M.endeavouri, Metapenaeopsis palmensis, M.stridulans, Trachypenaeus fulvus, and Parapenaeus longipes. Among the 14 penaeids, P.semisulcatus, M.ensis and M.palmensis were found to be the dominant species within each genus. There are seven existing fishing gears for shrimping in the Batan Bay and Tigbauan-Guimbal waters: fish corrals, lift net, filter net, gill net, skimming net, baby trawler and commercial trawler. In general, female penaeids are larger than males. The largest P.monodon female measured was 81 mm in carapace length with 23 g in body weight. The largest male measuring 59 mm in carapace length with 119 g of body weight was caught in Batan Bay. Judging from spermatozoa occurrence on both sexes of P.monodon, the biological minimum size for male is 37 mm in carapace length and 49 mm for female. A total of 133 Penaeus postlarvae obtained from the offshore were identified by comparison with those reared in the laboratory. The postlarvae of P.japonicus-latisulcatus complex were quite dominant (60 . 2%), followed by P.semisulcatus (18 . 0%), and P.merguiensis-indicus complex (17 . 3%). The number of P.monodon postlarvae was relatively small (4 . 5%). The modal carapace length of P.monodon postlarvae from the offshore was 1 . 3 mm with three or four dorsal and no ventral spines on the rostrum, while P.monodon fry from the shoreline had 2 . 3 mm with five or six dorsal and one or two ventral spines.

Developmental and ecological stages in the life history of milkfish Chanos chanos Forsskal

Seven stages in the life history of the milkfish C. chanos , are recognized and suggested: A, embryonic; B, yolksac larval; C, larval; D, postlarval; E, juvenile; F, subadult; G. adult. An outline is presented of the life history. It is concluded that the milkfish, throughout the known stages of their life history are well adapted and equipped for optimal survival. High swimming performance, broad flexibility in feeding habits, high adaptability to a wide range of physicochemical conditions of the environment are but a few of the adaptations. The main driving force in all developmental stages is the evolutionary response to food distribution and availability followed by predation pressure.

The Genomes of Oryza sativa: A history of duplications

We report improved whole-genome shotgun sequences for the genomes of indica and japonica rice, both with multimegabase contiguity, or almost 1,000-fold improvement over the drafts of 2002. Tested against a nonredundant collection of 19,079 full-length cDNAs, 97.7% of the genes are aligned, without fragmentation, to the mapped superscaffolds of one or the other genome. We introduce a gene identification procedure for plants that does not rely on similarity to known genes to remove erroneous predictions resulting from transposable elements. Using the available EST data to adjust for residual errors in the predictions, the estimated gene count is at least 38,000 - 40,000. Only 2% - 3% of the genes are unique to any one subspecies, comparable to the amount of sequence that might still be missing. Despite this lack of variation in gene content, there is enormous variation in the intergenic regions. At least a quarter of the two sequences could not be aligned, and where they could be aligned, single nucleotide polymorphism ( SNP) rates varied from as little as 3.0 SNP/kb in the coding regions to 27.6 SNP/kb in the transposable elements. A more inclusive new approach for analyzing duplication history is introduced here. It reveals an ancient whole-genome duplication, a recent segmental duplication on Chromosomes 11 and 12, and massive ongoing individual gene duplications. We find 18 distinct pairs of duplicated segments that cover 65.7% of the genome; 17 of these pairs date back to a common time before the divergence of the grasses. More important, ongoing individual gene duplications provide a never-ending source of raw material for gene genesis and are major contributors to the differences between members of the grass family.

The natural life history of milkfish

Following brief descriptions of the various phases in the natural life history of the milkfish (Chanos chanos), namely adults, eggs and embryos, larvae, fry and metamorphosis, juveniles and sub-adults, a summary is provided of the life history, providing also a schematic diagram.

The history of fish communities, biodiversity and environment of Lake Victoria and the lessons learnt

The first fishery survey of Lake Victoria was conducted between 1927 and 1928 (Graham 1929). Atthat time, the lake had a diverse fish fauna and the fishery was dominated by two endemic tilapiine cichlids; Oreochromis esculentus (Graham 1929) and O. variabilis (Boulenger 1906). There were a number of other species such as Protopterus aethiopicus Heckel 1851, Bagrus docmac (Forsk.) 1775, Clarias gariepinus (Burchell), Barbus species, mormyrids, Synodontis spp, Schilbe intermedius (Linn.) 1762 and Rastrineobola argentea Pellegrin, 1904 that were also abundant in the lake most of which made a significant contribution to the fishery (Graham 1929, Worthington 1929, 1932, Kudhongania & Cordone 1974). Haplochromine cichlids were represented by at least 300 species more than 99% of them endemic (Greenwood, 1974; Witte et al., 1992 a & b). The fishery of Lake Victoria was similar to that of lakes Kyoga and Nabugabo (Worthington 1929; Trewavas 1933; Greenwood 1965, 1966; Beadle 1962, 1981). There were also important fisheries on the inflowing rivers of Lake Victoria, the most important of which were Labeo victorianus and Barbus altianalis (Cadwallader 1965). The small sized species notably Rastrineobola argentea and haplochromines cichlids were not originally commercially exploited.

Laboratory measurement of strength mobilisation in kaolin: Link to stress history

This letter presents data from triaxial tests conducted as part of a research programme into the stress-strain behaviour of clays and silts at Cambridge University. To support findings from earlier research using databases of soil tests, eighteen CIU triaxial tests on speswhite kaolin were performed to confirm an assumed link between mobilisation strain (γ M=2) and overconsolidation ratio (OCR). In the moderate shear stress range (0.2c u to 0.8c u) the test data are essentially linear on log-log plots. Both the slopes and intercepts of these lines are simple functions of OCR.

Diatom community succession in the recent history of a eutrophic Yunnan Plateau lake, Lake Dianchi, in subtropical China

Fish introduction, eutrophication and disappearance of aquatic vegetation are important disturbances of aquatic ecosystems, especially in plateau lakes, which are generally considered to be very vulnerable. Fish were introduced to Lake Dianchi, a eutrophic plateau lake in southwest China, in the late 1950s and 1970s. After the introduction, invasive fish became the dominant species, and the total fish yield increased. Meanwhile, the trophic level of Lake Dianchi had a tendency to increase in the past decades because of the increases in human activities in the watershed area. In addition, the area of aquatic vegetation decreased from more than 90 to 1.8% of the lake area from the 1950s to 2000. This study investigated the effects of fish introduction, eutrophication and aquatic vegetation on the diatom community of Lake Dianchi by examining the changes of microfossil diatom assemblage and abundance. Results showed that the absolute abundance and diatom assemblages changed after fish were introduced. The endemic species, Cyclotella rohomboideo-elliptica, disappeared with the introduction of fish and increasing trophic levels after 1958. Fragilaria crotonensis entered into the lake with the introduction of fish and gradually thrived in the lake after 1958. Diatom species numbers also decreased gradually from 21 to 9 from the past to present. Epiphytic diatoms disappeared with the decrease of aquatic vegetation after 1985. Our study indicated that eutrophication was the most important process determining diatom abundance, and fish introduction was a secondary process determining diatom abundance, while aquatic vegetation had a more important role in structuring the diatom community in this eutrophic plateau lake.

Origin of Gymnocypris przewalskii and phylogenetic history of Gymnocypris eckloni (Teleostei : Cyprinidae)

The origins and phylogenetic patterns were assessed for G. przewalskii and G. eckloni by analyzing the complete mtDNA cytochrome b gene sequence (1140bp). Phylogenetic analyses further supported that there were three mtDNA lineages (A-C) identified in G. przewalskii and G. eckloni, demonstrating that outer rakers of the first gill have little significance in the phylogeny of the Gymnocypris fishes. The network established showed that G. eckloni of the Yellow River specific haplotype A1 was a founder and it radiated all haplotypes of G. przewalskii which suggested G. przewalskii might only originate from one of two maternals of G. eckloni from the Yellow River. Fs test and mismatch analysis showed at least two expansion events in the population of G. przewalskii about 0.2734 Ma and 0.0658 Ma, while G. eckloni from Qaidam Basin could have experienced severe bottleneck effect about 0.0693 Ma. The population expansion was detected in subclades A1 and A21 with the most recent common ancestor (TMRCA) about 0.2308 +/- 0.01 Ma and 0.1319 +/- 0.015 Ma, respectively, which were within the geological age range of "Gonghe Movement" event that caused the separation of Lake Qinghai from the upper Yellow River. These results suggested the effect of the fish diversification by rapid uplift of the Qinghai-Tibetan Plateau in the Late Pleistocene.

Changes in the life history of Abbottina fivularis in Lake Fuxian

After invading Lake Fuxian, China, Abbottina rivularis showed marked changes in its life history traits, including alterations in annuli formation, extension to the length of the breeding season, and an increase in fecundity and growth rate. The results are explained in the context of the enemy release hypothesis. (c) 2007 The Authors. Journal compilation (c) 2007 The Fisheries Society of the British Isles.

Rearing of Procypris rabaudi during early life-history stages

The early life-history of Chinese rock carp Procypris rabaudi was investigated during a 56-day rearing period: 318 artificially propagated P. rabaudi larvae were reared throughout metamorphosis in a small-scale recirculation system (345 L water volume, 10 x 18 L rearing tanks, 150 L storage and filter compartment with bioballs, 20-30 larvae L-1) at the Institute of Hydrobiology, Wuhan, Hubei Province, China. The newly hatched larvae had an initial total length of 8.93 +/- 0.35 mm SD (n = 10) at 3 days post-hatch and reached an average total length of 33.29 mm (+/- 1.88 mm SD, n = 10) 56 days after hatching. Length increment averaged 0.45 mm day(-1), resulting in a mean growth of 24.4 mm within the 56-day period. High mortality rates of up to 92% derived from an introduced fungus infection and subsequent treatment stress with malachite green. Our results indicate that Chinese rock carp can be raised successfully from artificially fertilized eggs. We therefore assume this species to be a candidate for commercial aquaculture.

Life history and production of Sphaerium lacustre (Mollusca : Sphaeriidae) in a shallow subtropical Chinese lake

A fingernail clam, Sphaerium lacustre, was studied in subtropical Lake Donghu from June 1999 to May 2000. The S. lacustre population was characterized by a single annual reproduction period starting in March and ending in October; the population comprised three size groups, of which the 1999 cohort was dominant. The annual average density and biomass were 100.2 ind./m(2) and 12.11 g/m(2), respectively The annual production was 43.02 wet weight g/m(2), and the corresponding annual production/biomass ratio was 3.55.

Life history characteristics of three types of females in Brachionus calyciflorus Pallas (Rotifera) fed different algae

This study describes the life history characteristics of amictic, unfertilized mictic and fertilized mictic females of the rotifer Brachionus calyciflorus cultured individually on two different algae at 0.1 mg ml(-1) food concentration and 27 degreesC. The duration of the juvenile period of amictic females was significantly shorter on Chlorella pyrenoidosa Chick than on Scenedesmus obliquus Kutz or both algae together. The duration of the juvenile period of unfertilized mictic females was significantly longer, and the number of eggs produced by amictic females was significantly larger on Chlorella pyrenoidosa than on S. obliquus. When fed the same type of alga, the duration of the juvenile period of the fertilized mictic females was the longest among the three types of females, and the durations of the reproductive period of the amictic females and the post-reproductive period of the fertilized mictic females were longer than, or equal to those of the other two types of females, respectively. The number of eggs produced by an unfertilized mictic female was the largest among the three types of females, and that of amictic females was larger than or equal to that of fertilized mictic females, depending on the type of diet.