Stocking Density, Growth and Survival Rate of Post-Settled Juveniles of Holothuria scabra (Jaeger 1833) Reared in an Ocean-Based Floating Hapa

Ocean-based nursery system using floating hapa have proved to be the best option for raising early sandfish juveniles. However, the nursery system can be further improved by providing key information that will support their application. The present study provides information on the effect of stocking density on growth and survival of sandfish juveniles reared in floating hapa (1 x 0.5 x 1 m). Three densities were tested, 100, 200 and 400 early juveniles (5 mm; 0.093 g) per hapa net in a randomized set-up. Initial density of 100 and 200 showed significant higher growth rate and final size (0.082–0.074 g/day; 3.76–3.42 g) compared to 400 (0.045 ± 0.002 g/day; 2.11 ± 0.07 g). Moreover, at 100 and 200 densities, > 95% of all juveniles attained release size (2 g) and only 74% for 400 density after 45 days of rearing. Sandfish juveniles showed negative allometric growth and their survival did not display any pattern (100 = 91%; 200 = 35%; 400 = 51.3%). The coefficient of variation for weight of juveniles showed strong positive relationship with initial density (R2 = 0.99, p = 0.039) with CV values of (100 = 48.6%; 200 = 49.8%; 400 = 50.1%). It is therefore concluded that, 100 stocking density should be opted for optimum results, however, 200 can also be considered provided that, the survival is improved. Keywords: Sea cucumber; Ocean-based Nursery; Stocking density; Survival rate; Growth rate

Influence of Recorded Pattern on Background Interference impact in Magnetic Recording

This paper discusses the impact of background interference on a recorded pattern for heat-assisted magnetic recording technology (HAMR). Several patterns of the background track were examined, with the log bit error rate and signal to noise ratio measured via a spin-stand tester using HAMR head and media. It was found that the low frequency pattern gave the highest BER and SNR loss due to the strong magnetic field from the adjacent tracks. Similar to its practical use, the PRBS pattern also showed high interference. These observations may be used to support HDD areal density growth.

Associations Between Cellular Levels of ATP and Prodigiosin Pigment Throughout the Growth Cycle of Serratia marcescens

ABSTRACT Serratia marcescens is a prolific producer of the red, membrane-associated pigment prodigiosin. Earlier work has established both a positive role for prodigiosin in ATP production during population lag phase and a negative role during high-rate, low cell density growth. This study uses the growth rate and growth phase modulation afforded by chemostat culture to extend prodigiosin functional analysis to the high density and stationary phases. Cellular levels of prodigiosin were positively associated with cellular levels of ATP during high-density growth, and artificial pigment induction during this phase increased cellular ATP. Following peak high density ATP per cell, early stationary phase enabled significant population growth while prodigiosin levels remained high and ATP declined. During late stationary phase, ATP per cell was positively associated with prodigiosin per cell while both declined during continued growth. These results provide correlational evidence for multiple effects of prodigiosin pigment on ATP production throughout the growth cycle. Earlier work and the data presented here enable formulation of a working model for the oscillating relationships between cellular levels of ATP and prodigiosin during batch culture.

Modification of Structural Properties Using Process Parameters and Surface Treatment of Monolithic and Thin-Walled Parts Obtained by Selective Laser Melting

Additive manufacturing is one of the most popular technological processes and is being considered in many research works, a lot of which are related to thin-walled parts analysis. There are many cases where different part geometries were manufactured using the same process parameters. That kind of approach often causes different porosity and surface roughness values in the geometry of each produced part. In this work, the porosity of thin-walled and monolithic parts was compared. To analyze additively manufactured samples, porosity and microstructural analyses were done. Additionally, to check the influence of process parameter modification on the manufactured parts’ properties, hardness and roughness measurements were made. Surface roughness and the influence of surface treatment were also taken into account. Porosity reduction of thin-walled parts with energy density growth was observed. Additionally, a positive influence of slight energy density growth on the surface roughness of produced parts was registered. Comparing two extreme-parameter groups, it was observed that a 56% energy density increase caused an almost 85% decrease in porosity and a 45% increase in surface roughness. Additional surface treatment of the material allowed for a 70–90% roughness reduction.

Characterization of Arthrospira platensis cultured in wastewater of Clarias catfish farming media: DNA barcode, helical form, growth, and phycocyanin

Wijayanti M, Syafudin M, Yulisman, Nurianti Y, Hidayani A, Gofar N. 2020. Characterization of Arthrospira platensis cultured in wastewater of Clarias catfish farming media: DNA barcode, helical form, growth, and phycocyanin. Biodiversitas 21: 5872-5883. Arthrospira production technology in catfish waste media can be an alternative to reduce environmental pollution. However, some environmental factors such as nutrition, light, and water content can influence characterization of Arthrospira at the genetic and physiologic level. Arthrospira platensis is one of the phycocyanin-producing cyanobacteria and can be cultured using catfish culture wastewater. Water quality especially pH and salinity can effect of growth rate and residue of phycocyanin from Arthrospira platensis. This study aimed to identify the species and morphological forms of Arthrospira cultured using technical fertilizer and waste media, as well as to know the phylogenetic trees between species in this study and the GeneBank based on the 16S rRNA gene, and determine the optimum of pH and salinity required in the medium of catfish culture wastewater to phycocyanin maximum production of Arthrospira. The optimation of pH and salinity method used Completely Randomized Design (CRD) factorial with 2 factors consisting of the first factor with 3 treatments and the second factor with 4 treatments and 3 replications. The first factor was pH of culture medium i.e. pH 6.5 ± 0.2, pH 8.5 ± 0.2 and pH 10.5 ± 0.2. The second factor was salinity of culture medium, that was salinity 0 ppt (parts per thousand/‰), 10 ppt, 20 ppt, and 30 ppt. Parameters observed in Arthrospira include density, growth rate, rendement of phycocyanin, and decreased total nitrogen and phosphate content in culture media. The results showed that morphology Arthrospira cultured on technical fertilizer media (AF) had a longer and helix filament compared to Arthrospira cultured on waste media (AW) which showed several linear and shorter filaments. Both samples have a genetic distance of 0.068 (6.8%). Phylogenetic trees indicated that AF had a close relationship with Arthrospira platensis petH from Japan (bootstrap value 95%). While AW formed a separate sub-cluster of AF isolates and Arthrospira platensis petH from Japan (bootstrap value of 85%). The best treatment in this study was P2S3 (pH 8.5 ± 0.2 with salinity 20 ppt), which produced 0.867 grams maximum density, growth rate of 22.026 %.day-1 and 11.347 mg.g1 rendement of phycocyanin.

The influence of wet feed distribution on the density, growth rate and growth variability of Tenebrio molitor

Mealworm larvae have the potential to be a future food and feed. One of the difficulties in rearing mealworms efficiently, is their need for both dry and wet feed. Extensive research has been done on dry feed and distributing this feed is easy with the existing technology. However, the wet feed (frequently chopped up vegetables) comes with several challenges. The nature of the wet feed (neither solid nor liquid) complicates automation, making manual feeding still the norm in many farms. This may result in an unequal distribution of the wet feed. The goal of this study was to assess the influence of distance to the wet feed (substituted by agar) on density, growth rate and growth rate variability of mealworm larvae. The entire larval growth stage was assessed from less than 1 mg up to more than 100 mg, as differences in mobility were expected for different sized larvae. The results indicate that the distribution of the agar plays a major role in the distribution and growth of the larvae, with less larvae and a decrease in growth rate observed when the agar was more than 5 to 10 cm away from the larvae. Few mealworms were found more than 15 cm from the agar, and their growth was inhibited resulting in a biomass up to 150 times lower than near the agar. The effects were mainly observed in larvae weighing less than 30 mg, heavier mealworms were mobile enough to crawl to and from the agar. Based on the results, and in order to ensure that all larvae sizes grow equally well and are well distributed in the crate, we strongly advise against distances of 10 cm or more and we recommend the placement of wet feed within 5 cm from the larvae.