Changes in leaf water use after removal of leaf lower surface hairs on <Emphasis Type="Italic">Mallotus macrostachyus</Emphasis> (Euphorbiaceae) in a tropical secondary forest in Malaysia

Leaf hairs may assist in maintaining high leaf water use efficiency in tropical secondary forest tree species. We compared leaf temperature, transpiration, photosynthesis and water use efficiency between hairy and depilated leaves in Mallotus macrostachyus (Euphorbiaceae), to determine the role of leaf hair in leaf water use efficiency (WUE) in tropical degraded secondary forest in Malaysia. Measurements were made on five mature individuals growing in sun-exposed conditions and five in shaded conditions. The hair dry weight per unit leaf area was significantly greater in sun leaves than in shade leaves. The transpiration rate (Tr_max) of depilated leaves in sun-exposed conditions was slightly higher than in hairy leaves in both morning and afternoon measurements. In contrast, Tr_max in the shade leaves was almost identical in hairy and depilated leaves. Leaf stomatal conductance (g _s) in the morning showed almost the same value among leaf types and light conditions. In the afternoon, g _s slightly decreased from the morning values in both sun and shade conditions. In the morning, the leaf water use efficiency (A _max/Tr_max) in both conditions did not differ significantly between hairy and depilated leaves. However, in the afternoon, WUE in the depilated leaves was significantly lower than in hairy leaves in sun-exposed conditions. These observations suggest that leaf hairs in M. macrostachyus contribute to the high leaf water use efficiency in drought conditions, such as high vapor pressure deficit experienced at midday in degraded tropical secondary forests.     

Quantitative analysis of reusing agricultural water to compensate for water supply deficiencies in the Nile Delta irrigation network

The main problem facing farmers in the Nile Delta is water shortages at the ends of irrigation networks and canals. These problems have worsened as water demands have increased. Egypt’s Ministry of Water Resources and Irrigation is currently trying to avoid water deficits by returning agricultural drainage water to the irrigation canals. In the Kafr El-Sheikh Governorate, some canals have an oversupply in some months and deficits in others. Ministry officials started a project by constructing culverts connected canal ends with the main drain (Bhr Nashrat) to provide supplemental agricultural drainage backflows (SADB) channeled through these culverts. However, this return is not controlled, and flows are based only on differences in the hydraulic head. In this study, we evaluated the effectiveness of SADB to counteract water shortages when the water supply from head regulators (WSHR) is insufficient. Our analysis considered the adequacy of the water supply and indicators of dependability and equity of supply. We tested two water supply conditions: (1) WSHR only and (2) WSHR plus SADB. During the summer (May–September) of 2008, SADB significantly improved the system’s ability to meet the irrigation water requirements (IWR) in some months. Adequacy and dependability, therefore, improved from “fair” to “good.” During the following winter (October–April), SADB improved adequacy and equity only in March and April, since water availability was generally sufficient under WSHR.     

Enzymatic solubilization of collagen in the skin of diamond squid Thysanoteuthis rhombus: application of a fungal acid protease

Enzymatic solubilization of collagen from the skin tissue of diamond squid Thysanoteuthis rhombus, an underutilized resource in Japan, was attempted using an acid protease from the fungus Rhizopus niveus. This novel approach was compared with the conventional method using porcine pepsin. Both proteases were able to solubilize most of the skin collagen (>90 % of the total collagen) by performing the treatment in 0.5 M acetic acid at 4 °C for 72 h and at an enzyme/substrate ratio (w/w) of 1/10. The SDS-PAGE patterns of the solubilized collagen preparations were quite similar to each other, and two types of collagen (major and minor collagens) were purified from each preparation by cation-exchange column chromatography. These collagen types from the porcine pepsin-solubilized collagen showed similar features to those from the Rhizopus acid protease-solubilized collagen. These results suggest that the Rhizopus acid protease, a protease of non-animal origin, is applicable for solubilizing collagen in the skin of diamond squid.     

Temporal fluctuation in the abundance of alginate‐degrading bacteria in the gut of abalone Haliotis gigantea over 1 year

In this study, we identified and enumerated alginate‐degrading bacteria in the gut of abalone over 1‐year period. From a total of 360 colonies growing on agar medium enriched with alginate, 251 isolates (70%) had the ability to degrade alginate. In addition, a high number of viable alginate‐degrading bacteria were detected throughout the survey period. Alginate‐degrading bacteria were more abundant in the cold season relative to the summer season (10⁷ vs. 10⁴ CFU g^?1, respectively). Strong positive correlation was also observed between the number of alginate‐degrading bacteria and feed intake (R = 0.854; P < 0.01). The identified alginate‐degrading bacteria comprised of 35 species grouped into 11 genera including Algibacter, Formosa, Polarybacter, Tamlana, Tenacibaculum (CFB group), Roseobacter, Ruegeria, Silicibacter (α‐proteobacteria), Agarivorans, Shewanella and Vibrio (γ‐proteobacteria) respectively. More than 80% of the isolated alginate‐degrading bacteria belonged to the genus Vibrio, showing high homology to Vibrio cyclotorophicus, Vibrio splendidus, Vibrio halioticoli and Vibrio neonatus. Based on the results, it was suggested that algal‐polysaccharide (alginate) degrading bacteria (mainly Vibrio) commonly exist in the gut of abalone and may play an important role in the degradation and digestion of the host's feed.     

Prevention of hypermelanosis by rearing Japanese flounder Paralichthys olivaceus in net-lined tanks

Fisheries Science - In artificially reared flatfish, especially the Japanese flounder Paralichthys olivaceus, pigmented skin (hypermelanosis) frequently appears on the fish’s blind side after...     

Hot-water solubility of mantle collagens in several cephalopod molluscs

The mantle muscles of five cephalopod species, Todarodes pacificus, Photololigo edulis, Sepioteuthis lessoniana, Sepia esculenta, and Sepia longipes, were extracted with 0.1 M NaOH to prepare crude collagen fiber, called ‘residue after alkali extraction’ (RS-AL). Solubility of the collagens in water was examined in the temperature range 20–90°C. The collagens showed a similar tendency in solubility, which gradually increased depending on the treating temperature, and the values at 40–90°C were constantly less than 47.0% for all the species examined. In addition, the collagens were estimated to denature in the approximate temperature range of 37.5–42.5°C. These results suggest that the collagens in RS-AL from these species may have relatively high resistance to hot-water extraction even after their denaturation.     

Swimming angle and target strength of larval Japanese anchovy (<Emphasis Type="Italic">Engraulis japonicus</Emphasis>)

The swimming angle of larval Japanese anchovy (Engraulis japonicus) was measured in a tank, and target strength (TS) was calculated using a theoretical scattering model. The mean swimming angle was 12.8° (SD ±22.1). Increased speeds of flow led to increased mean swimming angles. The mean swimming angle at flow of 5 cm s⁻¹ was higher than at other speeds. TS values were estimated using a distorted-wave Born approximation model for two cases. Average values were 1–3 cm s⁻¹ (11.5° ± 22.1) and 5 cm s⁻¹ (16.6° ± 21.7) for cases 1 and 2, respectively. For case 1, TS ranged from −92.0 to −74.7 dB with a mean of −79.4 dB at 120 kHz. For case 2, TS ranged from −92.2 to −75.2 dB with a mean of −79.9 dB. The mean TS in case 2 was lower than that in case 1, with the maximum difference being 1.0 dB at 120 kHz (standard length 22.0 mm). However, there were no significant differences between the regression lines of cases 1 and 2. Thus, changes in flow speed altered the swimming angle of larval Japanese anchovy, but had little influence on TS.     

Effects of turbidity on survival of larval ayu and red sea bream exposed to predation by jack mackerel and moon jellyfish

We conducted laboratory experiments to examine the effects of turbidity on the survival of red sea bream Pagrus major and ayu Plecoglossus altivelis altivelis larvae when exposed to either visual (jack mackerel juveniles) or tactile (moon jellyfish) predators. The experiments were conducted in 30-l tanks with three different levels of turbidity obtained by dissolving 0, 50, or 300 ppm kaolin. Predators were introduced to the experimental tanks followed by larvae of either red sea bream (mean ± standard deviation 6.1 ± 0.3 to 11.4 ± 2.1 mm standard length) or ayu (6.6 ± 0.3 and 24.4 ± 1.8 mm). When exposed to jack mackerel, the mean survival rate of larvae was significantly higher in 300 ppm treatments compared with the other turbidity levels. When exposed to moon jellyfish, however, there was a less marked difference in the survival rates among different turbidity treatments. Survival rates of ayu larvae exposed to moon jellyfish were generally lower than those of red sea bream. Our study indicates that anthropogenic increases of turbidity may increase the relative impact of jellyfish predation on fish larvae.