Length-weight relationship and relative condition factor of the sultan fish, leptobarbus hoevenii broodstock farmed in earthen ponds

The present study was aimed to assess the general health condition of Sultan fish, Leptobarbus hoevenii broodstock through their length-weight relationship (LWR) and relative condition factor (RCF). This broodstock was poly-cultured with the other carp’s species in earthen ponds. Totally, 95 broodstock (35 females and 60 males) were examined in this study. The total length (cm) and body weight (g) ranges of the L. hoevenii broodstock were 32.8 – 43.0 cm and 460 – 1,400 g for the females, while 30.0 – 44.5 cm and 285 – 1,300 g for the males, respectively. The b value of the females was 3.10 (> 3.0), indicating that they have attained positive allometric growth. In opposite, the males and the overall populations have attained negative allometric growth as their b value was 2.66 and 2.92 (< 3.0), respectively. All of these LWRs were significant at α = 0.01 with their correlation coefficient (r) values at 0.88 - 0.90. However, the 95% confidence interval of these b values were in the range of 2.32 – 3.64; they included 3.0 and overlapped each other. This result showed that these b values were not significantly different, indicating that the fish has achieved ideal growth. In addition, the relative condition factors of both females and males have achieved more than 1 (1.04 and 1.01, respectively), indicating that they have achieved their expected weight. Further observation on the LWR of the male L. hoevenii broodstock from the wild is necessary to confirm its optimum b value. Overall, the b value of the broodstock was 2.92 (close to 3), and their RCF value was 0.98 (close to 1). Therefore, the broodstock can be considered in good health condition. However, the influence of poly-culture management on the LWR of this broodstock should be examined in future studies

Malaysian herbs as feeding attractants and enhancers for the giant freshwater prawn (Macrobrachium rosenbergii) and the whiteleg shrimp (Litopenaeus vannamei)

Feeding attractiveness of 21 fresh herbs was examined for the giant freshwater prawn (Macrobrachium rosenbergii) and the whiteleg shrimp (Litopenaeus vannamei) at different growth stages in tanks. The feeding attractant and enhancement were assessed by behavioural observations of the test animals in response to pelleted feeds incorporated with the herbal extracts in different concentrations. For M. rosenbergii, peppermint (Mentha piperita) and dokudami (Houttuynia cordata) were the most attractive herbs at all stages, and garlic (Allium sativum) strongly attracting to the juveniles but only weekly to the adults, postlarvae and larvae. Peppermint significantly enhanced feeding of M. rosenbergii at all stages except for the larvae. Garlic was a significant feeding enhancer for M. rosenbergii juveniles and postlarvae. The inclusion of the herbal extract at high concentrations had a negative effect on the feeding. As far as L. vannamei is concerned, the red chilli (Capsicum annuum) was the best feeding attractant and ginger (Zingiber officinale) and peppermint were moderate attractants for adults and juveniles. While galangal (Alpinia galangal), ginger and yellow onion (Allium cepa sp.) enhanced feeding in L. vannamei adults, but red chilli, garlic and peppermint did not enhance feeding. Evidently, the strong feeding attractants were not necessarily effective feeding enhancers. The incorporation of several herb extracts at higher concentrations caused a negative effect on the feeding of the test animals. This could be due to the presence of feeding deterrents in the herb such as saponins which are known to lower food palatability in insect, decapod crustaceans and fishes. More long-term work is warranted to determine if inclusion of feeding enhancing herbs in artificial feed promotes growth performance of the shrimp

Observation on the embryonic development of Sultan fish, Leptobarbus hoevenii

Sultan fish, Leptobarbus hoevenii, is a popular freshwater fish species that is important to the aquaculture industry in some Southeast Asian countries, including Malaysia and Thailand. This study examined the embryonic development of L. hoevenii in order to fill in the biological knowledge gap and to provide a baseline information to fish farmers for the operations of mass seed production. The fertilized egg of L. hoevenii was obtained through natural spawning with the aid of hormones injection. Egg specimens were sampled randomly for the embryonic development examination. At a water temperature of about 28˚C, the egg fertilization ratio was 85.4%. The egg developed through the cleavage period, morula and gastrula stages, the segmentation periods, and the complete embryo formed at 18 hrs 11 minutes after fertilization (AF); some newly hatched were already seen at this stage. The egg hatching event completed at 22 hrs and 44 minutes AF, and the egg hatching ratio was 87%. Evaluation of the impacts of the water parameters (including temperature), ambient (e.g. water flow and lighting) and broodstock conditions (e.g. age and nutritional status) on the embryonic development duration in L. hoevenii is recommended for future studies

Vision-mediated feeding behaviour of early juvenile Sultan fish, Leptobarbus hoevenii

The Sultan fish, or ‘Jelawat’, Leptobarbus hoevenii is a cyprinid with a natural distribution in streams, rivers and lakes of some Southeast Asian countries, including Malaysia and Thailand (Mohsin & Ambak, 1983; Vidthayanon et al., 1997). It has value as a freshwater food fish (Mohsin & Ambak, 1983; Roberts, 1989), and its flesh is rich in protein, vitamin B and minerals (Tee et al., 1989). The Sultan fish has been introduced into several countries, including Taiwan and China, for aquaculture and as an ornamental species (Liao et al., 2001; Xiong et al., 2015). Captive breeding, seed production and farming techniques of this fish have been established (Liao et al., 2001; Meenakarn, 1986; Saidin et al., 1988; Truong et al., 2003), and there is information available about its feeding and nutritional requirements (Au et al., 2020). However, the major sensory modalities used by L. hoevenii at early life-history stages to detect prey are still unknown

Reproductive characteristics of the pond-farmed Sultan fish (Leptobarbus hoevenii)

Sultan fish (Leptobarbus hoevenii) is a high value freshwater fish, cultured in some Southeast Asian countries, including Malaysia and Thailand. However, information on its reproductive characteristics is very scarce. This study examined the gonadosomatic index (GSI), fecundity, egg diameter, and determined whether L. hoevenii is a single-or multiple-spawner. Twenty male and female pond-farmed L. hoevenii broodstock were obtained to measure their total length (TL), body weight (BW), and gonad weight to calculate the GSI. Ten females were randomly sampled from the 20 to determine their fecundity. A total of 1,500 eggs were sampled from each female. The egg diameter was measured then its frequency distribution was analyzed to detect the number of egg class group, and to determine whether L. hoevenii is a single-or multiple spawner. The female L. hoevenii examined were 32.2-47.1 cm and 350-1,200 g, while the males were 30.7-45.8 cm and 180-970 g in TL and BW, respectively. All female specimens contained gonads. The potentially smallest mature samples were recorded at 350 g (female) and 180 g (male). GSI for the female and male L. hoevenii were 1.81-12.28 % and 1.03-5.09 %, respectively. The fecundity was 35,467-128,067 eggs, while the highest fecundity was observed in a 1,000 g fish. The observed egg diameter ranged from 500 to 1,855 μm. Two to five groups of egg class were detected, indicating that L. hoevenii is a multiple spawner

Yolk-sac absorption, mouth size development, and first exogenous feeding of sultan fish, leptobarbus hoevenii

Sultan fish, Leptobarbus hoevenii is an important species for aquaculture in several Southeast Asian countries, including Thailand and Malaysia. However, knowledge on its yolk absorption, mouth size development, and first food ingestion timing is still lacking up-to-date. This information on the correct feeding of the L. hoevenii larvae are crucial to farmers. The present study hence examined these parameters in the L. hoevenii. The newly hatched L. hoevenii larvae were obtained through natural spawning with the aid of chemicals injection, and sampled consecutively every 2 hours to measure their yolk volumes, mouth height, and to confirm the ingestion time of the first Moina into the larval gut. Also, a starvation experiment was conducted to detect the larval point-of-no-return (PNR). It was found that the yolk sac volume of the newly hatched L. hoevenii larvae was 77.51 µm, and it was completely absorbed at 108 hours after hatching (hAH). The larval mouth has first opened at 36 hAH (mouth height 215±22.59 µm) but the larvae only commenced first exogenous feeding on Moina (approximately 207 μm in width) at 62 hAH, when its mouth height reached 372.91±79.11 µm. The L. hoevenii larvae required about 18 hrs from 62–80 hAH, to adapt themselves to feed on the given Moina, and the PNR was estimated to happen at 70–72 hAH. It was recommended that Moina should be given to the L. hoevenii larvae best within 62–72 hAH, at the rearing water temperature of 27 to 29°C

Sense organs development in larvae of the Sultan fish Leptobarbus hoevenii

At hatching, the sense organs of the Leptobarbus hoevenii larvae were morphologically immature. However, these sense organs had developed and became functional (including first occurrence of the intra-oral taste buds) to facilitate the larval first exogenous feeding at 3 days post-hatching (dph), before the yolk sac was completely absorbed at 5 dph. During the larval metamorphosis period (5–30 dph), the larval notochord flexion and fin development had completed. The retinal rods appeared at 5 dph, and its number increased with larval growth. The lagena was formed and the inner ears were fully calcified at 15 dph, indicating that the inner ears were completely developed. The olfactory organ development was completed when the anterior and posterior pits were formed at 30 dph. Canal neuromast was first found in the 30 dph L. hoevenii head portion, but none was observed at its trunk. Further examination of the elder stage (> 30 dph) of L. hoevenii is necessary to confirm the timing of trunk canal neuromast development. These findings have provided new biological information related to the L. hoevenii migratory life history in the field, as well as insight to improve the L. hoevenii larval rearing protocols

Valorization of Bokashi leachate as feed additive in tilapia farming

The Bokashi leachate (BL) is a by-product from the anaerobic digestion of food waste, following the Bokashi composting method. Bokashi leachate is acidic and it contains effective microorganisms hence it has potential to be a functional feed additive to the plant proteins based diets for fish farming. This study evaluated the growth performance and feed utilization of the red tilapia (Oreochromis sp.) fingerlings fed with the BL supplemented soybean meal (SBM) based diets. After an 8-week feeding trial, fish fed with the 5% BL supplemented SBM diet attained the highest weight gain. This result was significantly higher (p 0.05) to those fed with the control full fish meal (FM) diet. Generally, dietary inclusion of BL enhanced the fish feed intake on the SBM diet but it did not show clear sign of improvement in their feed utilization. In addition, no significant difference was found across the hepatosomatic index and viscerosomatic index from all dietary treatments. These outcomes concluded that dietary inclusion of BL can enhance the feed intake and growth performance of the red tilapia fingerlings fed with the SBM based diet without compromising their health, and the optimum BL inclusion level was 5%. Nevertheless, further study on the properties and substances content of the BL produced from different types and ratios of food waste is strongly recommended. In this study, BL was also discovered to be capable of reducing the crude fiber content in the SBM diets. Such observation deserves a further exploitation on the application of BL to manipulate the crude fiber content in the plant proteins based diets in fish farming

Feeding and nutrient requirements of Sultan fish, Leptobarbus hoevenii: A review

Sultan fish (Leptobarbus hoevenii) is a commercially important freshwater fish with high potential for aquaculture production in the Southeast Asian countries, including Malaysia. Many studies have been focused on its nutrition and trophic biology but the feeding practices in the farming have not yet been reviewed. This paper reviews on nutritional management of L. hoevenii broodstock, larvae and juveniles in culture systems. In general, there are feeding guidelines developed for the L. hoevenii farming but they are not fully supported with the scientific studies. Knowledge on the larval developmental biology is lacking to fully understand the feeding ecology of this fish. In addition, there is a paucity of data on requirements of various major nutrients in L. hoevenii at different life stages. Further studies on these topics are essentially required to improve the feeding practices in the farming of L. hoevenii

Touch-sensitive bristles on the carapace of the mud crab Scylla paramamosain may be receptors for courtship signals

Bristle patches on the carapace behind the eyes were found for the first time in both males and females of the four species of mud crab Scylla spp. Electrocardiography revealed that the bristle patches of Scylla paramamosain were sensitive to touch (with a glass capillary) but not to chemical stimulation (with sugarcane juice). To elucidate the function of these touch signals, the courtship behaviour of S. paramamosain was video-recorded in a broodstock tank. A male approached a female, extended a walking leg over her carapace, touched her bristle patches with a dactyl, mounted her, and probed the bristle patches further with the third maxillipeds. Touch stimulus may be a signal for courtship in Scylla and one of the chain stimuli for the completion of mating behaviour.This study was partially funded by Universiti Malaysia Sabah grant SDK0028-2018