Taxonomic and genetic confirmed findings of snow crab (Chionoecetes opilio) larvae in the Barents Sea

The snow crab (Chionoecetes opilio) is an Arctic cold-water species native to the northwestern Atlantic Ocean and the northern Pacific Ocean. During the recent decades, a population has established in the Barents Sea. Several aspects of the snow crabs’ biology in this area have not been described, including time of hatching, intermoult duration of the different larval stages and larval distribution. Insight into the early-life stages might increase the understanding of the population's dynamics and further spreading in the Barents Sea as well as inform basis for making monitoring and management decisions. The present study investigated the presence and developmental stage of snow crab larva in plankton samples obtained in the central Barents Sea during a research survey in June and July 2019. Presence of snow crab larvae was confirmed through taxonomic and genetic identification. All larvae were identified as zoea I, which gives an indication of the timing of the hatching period. Morphological measurements coincide well with those reported in studies from the species native distribution range. No larvae of native Hyas spp. were found and overlap in temporal and spatial distribution is discussed. The study provides important information for development of further research into the biology of the snow crab in the Barents Sea.

Crab Larvae Counter Using Image Processing

Very small larval size, high mortality rate of crab larvae, the absence of an accurate crab larva counter at affordable price, the density of larvae that are not known accurately, the ratio of feed that not in accordance with the number of larvae to damage water quality and cannibalism, water quality can not be adjusted to the density of distribution, and economically unprofitable both in terms of feed efficiency and buying and selling transactions. By knowing the number of crab larvae accurately the survival rate of crab larvae increases and is economically beneficial. In this study larvae counters were designed and developed. This tool uses digital imagery to detect and count the crab larvae zoea-1 phase. The accuracy of crab larva counter is 89,8%.

SUBSTITUSI PENGGUNAAN NAUPLIUS ARTEMIA DENGAN PAKAN MIKRO DALAM PEMELIHARAAN LARVA KEPITING BAKAU, Scylla olivacea

Adanya molting death sindrom yang umumnya terjadi pada stadia zoea-5 ke megalopa dan ke krablet-1 pada kepiting bakau, Scylla olivacea, diduga berkaitan dengan ketidakcukupan nutrien yang dikonsumsi larva, sehingga perlu dicobakan penggunaan pakan buatan (mikro) pada stadia tersebut. Penelitian ini bertujuan untuk mendapatkan dosis optimum penggunaan pakan mikro (micro diet, MD) untuk mensubstitusi penggunaan nauplius Artemia (Art) dalam pemeliharaan larva kepiting bakau. Hewan uji yang digunakan adalah larva kepiting bakau stadia zoea-4—5. Hewan uji tersebut dipelihara dalam wadah bak fibre berisi air laut 150 L dengan kepadatan 12 ind./L. Perlakuan yang dicobakan adalah pemberian pakan uji berupa: nauplius Artemia sebanyak 100% (100% Art), nauplius Artemia 75% + pakan mikro 25% (75% Art + 25% MD), nauplius Artemia 50% + pakan mikro 50% (50% Art + 50% MD), nauplius Artemia 25% + pakan mikro 75% (25% Art + 75% MD), dan pakan mikro 100% (100% MD). Pemberian pakan uji dilakukan pada pagi dan sore hari selama 15 hari pemeliharaan (hingga larva mencapai stadia krablet-1). Hasil penelitian menunjukkan bahwa pada penggunaan nauplius Artemia 50% + pakan mikro 50% didapatkan sintasan krabet-1 tertinggi (5,6%) dan berbeda nyata (<0,05) dengan sintasan krablet pada penggunaan 100% nauplius Artemia (sintasan 2,4%) dan 100% pakan mikro (sintasan 2,1%). Bobot badan, lebar karapaks krablet, dan aktivitas enzim pencernaan relatif sama di antara perlakuan. Penggunaan pakan mikro dapat menggantikan 50% penggunaan Artemia dalam pemeliharaan larva (zoea-5 hingga krablet-1) kepiting bakau.Cases of molting death syndrome generally occur on the transitional stage of zoea-5 to megalopa stage and to crablet-1 of mud crab, Scylla olivacea. It is suspected that the event could be related to nutrient insufficiency consumed by the larvae which can be supplemented using artificial diet (micro diet). This study aims to obtain an optimum dosage use of the micro diet (MD) to substitute the use of Artemia nauplii (Art) in the crab-larva rearing. Test animals used were mud crab larvae of zoea-4—5 stadia. The test animals were reared in the fiberglass containers, filled with seawater as much as 150 L, and stocked with a density of 12 ind./L. The treatments tested were feeding tests in the form of: Artemia nauplii as much as 100% (100% Art), Artemia nauplii 75% + micro diet 25% (75% Art + 25% MD), Artemia nauplii 50% + micro diet 50% (50% Art + 50% MD), Artemia nauplii 25% + 75% micro diet (25% Art + 75% MD), and micro diet 100% (100% MD). The larvae were fed daily in the morning and afternoon for 15 days until the larvae reach crablet stage. The results showed that the use of Artemia nauplii 50% + 50% micro diets obtained the highest survival rate (5.6%) of crablet-1 and significantly different (<0.05) with the survival rates of crablet fed with 100% of Artemia nauplii (survival rate of 2.4%) and crablet fed with 100% micro diet (survival rate of 2.1%). Body weight, carapace width of crablet, and digestive enzyme activities were relatively similar between the treatments. The use of micro diet could replace 50% of the utilization of Artemia nauplii in larvae (zoea-5 to crablet-1) rearing of mud crab.

Positive phototaxis of the brine shrimp Artemia salina to monochromatic light

The brine shrimp Artemia salina was photopositive in response to monochromatic light of approximately equal quantum intensity of two absolute levels. At the higher level (about 3 × 1014 quanta s−1 cm−2), the spectral response was bimodal with peaks near 560 and 700 THz frequency (about 535 and 430 nm wavelength, respectively), with an antimode at about 640 THz (465 nm). Response at the lower level (about 2 × 1014) was slightly lower and the midspectrum peak was shifted to higher frequencies (shorter wavelengths) and depressed relative to the high-frequency peak near 700 THz. The results suggest that positive phototaxis is mediated by two visual pigments, the high-frequency (short-wavelength) pigment being activated at lower illuminations than the midspectrum pigment. A similar bimodal response is known from a crab larva, but this appears to be the first anostracan crustacean to have been tested.