Axial growth of hexactinellid spicules: Formation of cone-like structural units in the giant basal spicules of the hexactinellid Monorhaphis

The glass sponge Monorhaphis chuni (Porifera: Hexactinellida) forms the largest bio-silica structures on Earth; their giant basal spicules reach sizes of up to 3 m and diameters of 8.5 mm. Previously, it had been shown that the thickness growth proceeds by appositional layering of individual lamellae; however, the mechanism for the longitudinal growth remained unstudied. Now we show, that the surface of the spicules have towards the tip serrated relief structures that are consistent in size and form with the protrusions on the surface of the spicules. These protrusions fit into the collagen net that surrounds the spicules. The widths of the individual lamellae do not show a pronounced size tendency. The apical elongation of the spicule proceeds by piling up cone-like structural units formed from silica. As a support of the assumption that in the extracellular space silicatein(-like) molecules exist that associate with the external surface of the respective spicule immunogold electron microscopic analyses were performed. With the primmorph system from Suberites domuncula we show that silicatein(-like) molecules assemble as string- and net-like arrangements around the spicules. At their tips the silicatein(-like) molecules are initially stacked and at a later stay also organized into net-like structures. Silicatein(-like) molecules have been extracted from the giant basal spicule of Monorhaphis. Applying the SDS-PAGE technique it could be shown that silicatein molecules associate to dimers and trimers. Higher complexes (filaments) are formed from silicatein(-like) molecules, as can be visualized by electron microscopy (SEM). In the presence of ortho-silicate these filaments become covered with 30-60 nm long small rod-like/cuboid particles of silica. From these data we conclude that the apical elongation of the spicules of Monorhaphis proceeds by piling up cone-like silica structural units, whose synthesis is mediated by silicatein(-like) molecules. (C) 2008 Elsevier Inc. All rights reserved.

The influence of diets containing dried bivalve feces and/or powdered algae on growth and energy distribution in sea cucumber Apostichopus japonicus (Selenka) (Echinodermata : Holothuroidea)

In recent years, bivalve feces and powdered algae have been used as the food sources of holothurians in China. In this study, growth and energy budget for sea cucumber Apostichopus japonicus (Selenka) with initial wet body,veights of 32.5 1.0 g (mean +/- SE, n=45) when fed with five different granule diets containing dried bivalve feces and/or powdered algae in water temperature 13.2-19.8 degrees C and salinity 30-32ppt were quantified in order to investigate how diets influence growth and energy distribution and to find out the proper diet for land-based intensive culture of this species. Results showed that diets affected the food ingestion, feces production, food conversion efficiency and apparent digestive ratios, hence the growth and energy budget. Sea cucumbers fed with dried feces of bivalve showed poorer energy absorption, assimilation and growth than individuals fed with other four diets; this could be because feces-drying process removed much of the benefits. Dried bivalve feces alone, therefore, were not a suitable diet for sea cucumbers in intensive cultivation. The mixed diets of feces and powered algae showed promising results for cultivation of sub-adult Apostichopus japonicus, while animals fed with powdered algae alone, could not obtain the best growth. According to SGR of tested animals, a formula of 75% feces and 25% powdered algae is the best diet for culture of this species. Extruded diets were used in the present experiment to overcome shortcomings of the traditional powdered feeds, however, it seems a conflict exists between drying bivalve feces to form extruded diets and feeding sea cucumbers with fresh feces which contain beneficial bacteria. Compared with other echinoderms, in holothurians the energy deposited in growth is lower and the energy loss in feces accounts for the majority of the ingested energy. Such detailed information could be helpful in further development of more appropriate diets for culture of holothurians. (c) 2006 Elsevier B.V. All rights reserved.

Effects of the initial size, stocking density and sorting on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino

During winter months, a novel overwintering mode of transferring juvenile abalones to open seawaters in southern China rather than keeping them in closed land-based nursery systems in northern China is a popular practice. The initial size, stocking density and sorting are among the first considerations when establishing an abalone culture system. This study aimed to investigate the effects of these factors on the growth of juvenile Pacific abalone, Haliotis discus hannai Ino, during overwintering. Juvenile abalones were reared in multi-tier basket form for overwintering in open seawaters in southern China for 106 days. The daily growth rates (DGRs) in the shell length of all experimental groups ranged from 67.08 to 135.75 mu m day(-1), while the specific growth rates (SGRs) were 0.2447-0.3259% day(-1). Variance analysis indicated that both DGRs and SGRs in shell length were significantly affected by the initial body size and stocking density. Furthermore, the effects of stocking density on DGRs and SGRs varied with the initial size. However, sorting abalones according to their initial sizes may not be necessary in practice as sorting did not alter growth significantly at all densities in this study. Factors potentially affecting abalone growth such as genetic control and intraspecific competition were discussed.

Controlled growth of uniform silver clusters on HOPG

We have investigated growth of silver clusters on three different, i.e. normally cleaved, thermally oxidized and Ar+ ion sputtered highly oriented pyrolytic graphite (HOPG), surfaces. Scanning tunneling microscopy (STM) observations reveal that uniformly sized and spaced Ag clusters only form on the sputtered surface. Ar+ sputtering introduces relatively uniform surface defects compared to other methods. These defects are found to serve as preferential sites for Ag cluster nucleation, which leads to the formation of uniform clusters. (c) 2005 Elsevier B.V. All rights reserved.