Comparison of horseshoe crabs (Tachypleus gigas) morphometry between different populations using allometric analysis

Studies on horseshoe crabs morphometrics found that they have maintained their descendent features from the Late Ordovician Period to present day. In the present study, we applied the allometric study to evaluate the correlation of body growth in three populations of the Asian horseshoe crab (Tachypleus gigas) collected from Balok (Pahang), Cherok Paloh (Pahang) and Merlimau (Melaka), Malaysia, coastal areas. The aims of this study are to examine the logarithmic growth of horseshoe crabs between three populations by analyzing the variation of their body weight (BW), carapace length (CL), carapace width (CW) and telson length (TEL) to determine their growth and maturity. Their body parameters were analyzed by the allometric method. There are no significant differences between males weight in all populations (p>0.05). However, females from Merlimau were smallest (BW: 519.7±66.3 g; CL: 21.1±1.1 cm; CW: 19.6±0.9 cm) among the three populations; Balok (BW: 928.5±123.2 g; CL: 23.8±1.0 cm; CW: 23.3±1.0 cm) and Cherok Paloh (BW: 939.8±125.7 g; CL: 25.4±1.5 cm; CW: 25.1±1.6 cm). Males and females of T. gigas in Merlimau could be classified as less matured among Balok and Cherok Paloh, since the increment of CL/CW were higher than their BW. Further study on T. gigas allometry along Malaysian coastal area is needed to understand the variation growth between populations. The study could be an alarming condition to a particular T. gigas population

Morphometric study of horseshoe crab’s spawning population in a coastal area of peninsular Malaysia

Two Asian horseshoe crabs Tachypleus gigas and Carcinoscopius rotundicauda are commonly found on some coastal habitat in the east coast of Peninsular Malaysia during their spawning season. The number is small if compared to the Atlantic species, Limulus polyphemus which could be related to their foraging ground on sea bottom. It is not easy to ascertain the reason of the small landing population of horseshoe crab in the east coast of the Malay Peninsula. Some morphometric information on spawning population of horseshoe crab was studied at mangroves and sandy beach habitat in Balok coastal area of Pahang. Morphometric parameters measured in this study included body weight (Wt), inter-ocular length (IOL), dorsal prosoma breadth (DPB), dorsal body length (DBL), ventral prosoma breadth (VPB), telson length (TL), central height (CH), frontal length (FL), frontal margin height (FMH), and regional length (RL). Weight of T.gigas ranged from 290 to 1200g and 180 to 420g for female and male respectively while C. rotundicauda ranged from 260 to 340g and 100 to 260 for female and male respectively. Parameter with the highest mean value is weight. The lowest mean value was found for IOL with 88.64±6.62mm (male) and 120.42±9.95mm (female) and 62.87±14.39mm (female) and 77.0±6.57mm (male) for T.gigas and C. rotundicauda respectively. Statistically it was found that the males and females T. gigas could grow with the same rate in DPB and DBL. Nonetheless, male C. rotundicauda has the most increase of size of prosomal breadth in DPB than DBL. There was no evidence of imbalance growth of both sexes of the species collected from the study area. The findings indicate a good growth condition for both species. The relationship between the surrounding bottom habitat and the diet of horseshoe crab should be studied further to understand the contribution of sea bottom habitat to horseshoe crabs

Development of model system for cost-effective pico hydro turbine

One of the main obstacles of rural electrification programme is to find an alternative energy to replace power generated by generator. The ever increasing fuel price and its cost of transportation to the remote location limited the availability of electricity to certain time of the day. Since the rural settlement usually located near water source, renewable energy based on hydro is suggested. This paper will discuss about the development of model system for cost-effective pico-hydro turbine. The size of the turbine will be based on low flow and low head application. Two types of turbine, propeller or also known as axial-flow and cross-flow, are evaluated under these conditions. Both of the turbines were installed in one model system equipped with storage tanks and piping system. Centrifugal pump is used to ensure the circulation of the water between main storage tank into the flowing tank simulating the run-of river application for pico hydro system. The head of the model system is fixed with variable parameter of water flow rate is controlled by using controller valve and flow meter for power data collection for each turbine. The performance of both turbines were also simulated and evaluated by using CFD's software. Techno-economics evaluations are done so that the model of the system will be able to select the optimum size of the turbine based on the flow rate for a cheap efficient and costeffective hydro turbine

CFD anallysis on cost effective pico hydro turbine: A case study for low head and low flow rate condition

Pico-hydro turbine has been widely used for off-grid settlement especially for stand-alone domestic application. Jn most cases there is a trade-off between the flow rate and the available head. The fluctuation of water flow rate between wet and dry seasons obviously affected the performance of the turbine. The problem is compounded when a specific turbine is used in low head and low flow application. This paper discusses the performance of an axial-flow (propeller) turbine in this particular condition. Evaluation is made based on the blade parameters in order to improve its existing performance. Comparisons are made between the current blade and a modified version of it, in term of hub to tip ratio and the number of blades used. The values of hub to tip ratio ranging between 0.4 to 0.7. The numbers of blades used are 3, 4, 5, and 6. Simulation analysis was done using Computational Fluid Dynamics (CFD) software. Analyses were done on each of the turbine blade to find the optimum stream velocity and power output which can be derived for each combination of turbine parameters.The analysis results show that with lowest value of hub to tip ratio which is 0.4 and the lowest number of blades which is 3, contributed the best performance of the axial-flow turbine

Ecdysis failure in Asian horseshoe crab larvae of Tachypleus gigas under laboratory observation

Horseshoe crab has recently been categorized as a halal commodity which exposed them to un-sustainable exploitation. As grouped among the arthropods, Asian horseshoe crab, Tachypleus gigas, rely on ecdysis to grow. The stage of ecdysis itself is the most crucial step in their life cycle and could cause death if it cannot be completed successfully. This study investigated the different types of ecdysis failure in the larval stage using Scanning Electron Microscope (SEM) technique. Samples of the molted skeleton that were left behind after the ecdysis process were immediately collected and prepared for SEM. Three types of molting failures were identified from the observation prosomatic failure, opishosomatic failure, and appendage failure. These failures were classified according to the position of the larvae body part where the exuviae were stuck at. Two out of three failures, pro-somatic and opisthosomatic ecdysis failure would cause death instantly as the exuviae stuck at the vital organ, gills, and prevent it to function well in the breathing process. The micrograph obtained from the SEM study could be an important record for an evolutionary and growth study of this living fossil. It will also contribute to the understanding of the conservation effort for the species

Feeding mechanisms of adult tropical horseshoe crab, Tachypleus gigas toward Feeds' conditions

Information on feeding behaviour of tropical horseshoe crabs, Tachypleus gigas (M¨uller, 1785) is still scanty compared to Limulus polyphemus (Linnaeus, 1758). Foods condition such as decayed, sheltered and etc., would substantially influence the edibility of food by the T. gigas. However, horseshoe crabs might have specific behaviour to manipulate the foraged food. The aim of this paper was to investigate the feeding mechanism of T. gigas toward different feed conditions. Experiments were conducted inside a glass tank. A total of 30 males and females respectively were introduced to five different natural potential feeds, namely, gastropods (Turritella sp.), crustacean (Squilla sp.), fish (Lates calcarifer ), bivalve (Meretrix meretrix ) and polychaete (Nereis sp.). We have manipulated the condition of introduced feed based on the several potential foods conditions in nature such as sheltered (protected with shell, hard outer skin or host tube), unsheltered and decayed before introduced the feeds to the crabs. In present study, female crabs took shorter response period towards surrounding feed compared to males. Overall, they prefer to consume freshly dead feeds and would totally reject the sheltered feeds, such as, shell, hard outer skin and tube host. Male crabs have particular feeding behaviours to manipulate the edibility of the decayed feeds. Detailed experiments on the feeding mechanism of T. gigas could provide more information on their foraging activity in the wild

Food intake, gut transit time and defecation pattern of Asian horseshoe crab, Tachypleus gigas

Nowadays, the numbers of wild horseshoe crab harvested for study are increasing. However, general information on Tachyplues gigas satiation level, gut transit time, defecation pattern and acclimation period in captivity during holding period are still scanty. The aims of this study are to identify T. gigas food intake, gut transit time and defecation pattern during the rearing period by introducing the crabs with gastropod (Turritella sp.), crustacean (Squilla sp.) and bivalve (Meretrix meretrix ) in several feed ratios; 0.2%, 0.6%, 1.0%, 1.4%, 1.8% and 2.2% expressed of crabs’ body weight. The defecation of T. gigas was monitored for every three hours after being fed to measure their gut transit time and defecation pattern. Male crabs did not significantly eat until two weeks in captivity, while the females started to eat in the early first week after being harvested from the wild. The satiation levels of the females (gastropod: 1.8%±0.04; crustacean: 1.7%±0.08; bivalve: 1.8%±0.06) were significantly higher than the males’ (gastropod: 1.7%±0.08; crustacean: 1.4%±0.02; bivalve: 1.6%±0.05) for all feed types. Gut transit time of the males were significantly longer than the females’. Male crabs took shorter time (1±0 hr) to achieve their satiation than female crabs (2±0 hrs). This study provides useful information for T. gigas rearing activity and for designing a better rearing system

Relations of coral reef benthos composition and horseshoe crabs’ gut content

Intensive earlier studies on horseshoe crab feeding ecology are focused on the Atlantic species, Limulus polyphemus (Linnaeus, 1758). However, the distribution of species, food abundance, and availability of benthos in a particular environment might influence the horseshoe crab's preference for diet in a particular region. The aims of this research are to analyse the benthos composition in Tachypleus gigas spawning site and coral reefs located near the spawning ground in Cherok Paloh, Pahang, and compare it with the food composition inside the T. gigas digestive track. A total of 30 samples of male and female horseshoe crabs, T. gigas respectively, were harvested by using a fishing net during the incoming high tide. Their guts were dissected, and the contents were analysed according to Squires and Dawe criteria. Results showed that echinoderm was the main food composition in the gut of males (54.27%) and females (51.44%) during the open sea migration phase. Amuk-amuk coral reef (3°41'51"N 103°24'13"E), Raja Muda coral reef (3°38'01"N 103°28'23"E) and Air Leleh coral reef (3°35'38"N 103°29'00"E) are the nearest sea urchin habitats to the sampling area. Benthos analysis showed higher echinoderm composition in those coral reefs (31.58 – 42.11%). There is no echinoderm composition found in the spawning site sediment. Further study is needed to provide reliable data on the significance of coral reefs in the horseshoe crab's foraging ecology

Morphology description of early larval stages of the Asian horseshoe crab, Tachypleus gigas, and their exuviae

Knowledge of the growth and ecdysis or molting process in horseshoe crabs as a primitive member of arthropods is limited. This study aimed to investigate the development and ecdysis in the Asian horseshoe crabs through a Scanning Electron Microscope (SEM) approach. The fertilized eggs of Tachypleus gigas were collected from the natural breeding site at Kg. Johor Lama, Johor, and brought back to the laboratory for incubation and hatching. The molted exoskeletons (exuviae) from the first and second ecdysis were collected right away after each molting process, carefully dried and further processed and critical-point dried before coated with gold. The same preparation was made to examine the morphological feature for instars. They were then examined with the SEM. All prosomal appendages are in a complete form during the first instar stage as well as in the exuviae. The second instar stage is noted with the presence of the telson. The exuviae for the first (from instar 1), and then the second molt (from instar 2) showed consistently the suture opening located along the anterior edge of the prosoma at the exuviation suture. This suture is absent from the exoskeleton which is still intact with the larvae. There are notably two hinge pores located at both ends of the hinge which is the central dorsal part that joins the prosoma and opisthosoma. These pores are absent on the intact larvae’s exoskeleton. The findings contribute to further improving the understanding of early growth and ecdysis in this living fossil

Feeding ecology and food preferences of Cherok Paloh, Pahang horseshoe crab, tachypleus gigas

Intensive previous studies on horseshoe crabs feeding ecology were mostly focus on Limulus polyphemus. Their food preference might be different depend on the availability and abundance of feeds in the particular environment. This paper aims to investigate the feeding ecology and food preferences of Cherok Paloh, Pahang Tachypleus gigas. Ten samples of male and female horseshoe crabs, Tachypleus gigas were trapped in fishing net during the incoming high tide and 10 samples of male and female were hand-harvested at the spawning beach during pre and post-mating respectively. Their gut content was analysed by the Electivity Index. Results showed that Tachypleus gigas coming to spawn with full gut content. Echinoderm served as a main food composition in the gut of males (50%) and females (51.94%) during the open sea migration phase. The main composition was substituted by macrophyte (males: 59.51% to 65.15%; females: 36.36% to 58.10%) as they arrived to shore. Based on Electivity Index, male crabs showed positive preference toward polychaete (EI: 0.04) and macrophyte (EI: 0.19) at the spawning site while, the females showed positive preference toward bivalve (EI: 0.46). Further study on feeding ecology is needed in order to improve the population of Tachypleus gigas in Malaysia