In this study, the gene expression levels of collagen metabolism-related factors (prolyl 4-hydroxylase (P4H α(I)), matrix metalloproteinase-9 (MMP-9), and tissue inhibitor of metalloproteinases-2 (TIMP-2)) in red seabream muscle were compared between fish reared by distinct farmers (RA and RB) to investigate the relationship of these genes to collagen content and texture (breaking strength) of red seabream meat. The meat breaking strength and muscle collagen content of RA were significantly higher than those of RB. The gene expression level of MMP-9 in RA was significantly lower than that in RB. On the other hand, the expression levels of P4H α(I), which is involved in collagen synthesis, and TIMP-2 were significantly lower in RA than those in RB. A similar relationship was observed when comparing of mature (soft) and non-mature (tough) fish. These results indicated that the gene expression of MMP-9, a degrader of collagen, is suppressed in rigid muscle tissue while expression of P4H α(I) and TIMP-2, positive effectors of texture and collagen synthesis, are synchronously down regulated. An approach focusing on balancing of collagen synthesis and degradation is necessary in the future studies.
In order to develop a suitable artificial diet for squid, this study investigated the influence of feed salt content on the feeding behavior of oval squid paralarvae Sepioteuthis lessoniana. Experimental feed was either artificial feed (surimi) pre-soaked in seawater or distilled water; or young anchovy Engraulis japonicus pre-soaked in seawater, distilled water, or one of 9 kinds of pure salt solution. The avoidance rate to these feeds was highest for diets pre-soaked in NaCl, and progressively lower in the order of seawater, MgCl2, KCl, and CaCl2. When experimental feeds had been subsequently washed with distilled water, the avoidance rate was reduced. Similarly, artificial feeds were avoided when they had been soaked in seawater, but not when soaked in distilled water. The suckers on the arms of oval squids of age 7 to 28 days were observed by histological staining to have cells on the infundibulum with similar morphology to chemoreceptor cells on the sucker infundibulum described for other cephalopods. It is therefore suggested that oval squids decide whether to accept or reject feed based on the detection of its salt content by chemoreceptor cells in the arm suckers.
We examined the effects of washing filter materials on the ammonia oxidation activity and ammonia oxidizing microorganisms. The experiment used porous filter materials, which enables attachment of nitrifying microorganisms, in the artificial seawater. Washing to remove detrital materials clogging the surface of filter materials resulted in an over two-fold increase in the ammonia oxidation activity. The ammonia oxidation activity of filter materials washed with artificial seawater decreased to 92% of the level before the washing. The relative abundance of an ammonia-oxidizing archaea and bacteria in the filter materials decreased to 94% and 86%, respectively. Washed water had an ammonia oxidation activity accounting for 15% of the total. Both ammonia oxidizing microorganisms were detected in the washed water originating from the flow out by washing the filter materials. Washing filter materials using water 10°C different from the bioreactor operating condition led to an ammonia oxidation activity decrease of less than 10%. The ammonia oxidation activity of the filter materials washed with freshwater decreased by approximately 25%, and immersion in tap water declined by 91%. To maintain optimal efficiency of the ammonia oxidation activity, the water used in washing should conform with the bioreactor operating conditions.
Egg cases with early-middle staged embryos of the oval squid Aka-ika, Sepioteuthis sp. 1, that were spawned on an anemometer set in the deeper layers of the coastal waters of the Ryukyu Archipelago, were collected in 2013, 2016, and 2017. However, of these only the egg cases collected in 2016 were used in this study as they had been kept in stressful conditions; packed without seawater and kept in a refrigerator at 8°C for approximately 25 h immediately after collection and were then raised under normal captive conditions in the laboratory in order to examine the effects that exposure to low temperature and oxygen levels had on later embryonic development, hatching, and hatched juveniles. We also investigated the overall feasibility of aquaculture of this species. Embryonic development proceeded followed by hatching, and the hatched juveniles survived for over 4 months. These records were compared to the survival and growth of Aka-ika Sepioteuthis juveniles not exposed to stressful conditions during their embryonic development that hatched from egg cases spawned on an artificial spawning bed set in the coastal waters of the Ryukyu Archipelago in 2016. This comparison revealed that Aka-ika Sepioteuthis embryos can develop, hatch, survive, and grow normally, even under severe stress conditions during early-middle embryonic development. This suggests that the gelatinous coat of the egg case in cephalopods might function as barrier against changeable environments during the early life phase.
Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are synthesized in the pituitary gland and play important roles in reproduction in teleosts. In this study, the pituitary structure, the immune signals of FSHβ subunit (FSHβ) and LHβ subunit (LHβ), and the localization of these hormones in the pituitary were investigated using four species of grouper. The pituitary in each species consists of the neurohypophysis (NH) and adenohypophysis (AH). The AH is further divided into the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intermedia (PI). FSHβ and LHβ immune signals were detected in the PPD and PI areas in the areolate, red spotted, and honeycomb groupers. However, in the longtooth grouper, although FSHβ signals were detected in the PPD and PI areas, LHβ signals were only detected in the PPD area. These results indicate that FSHβ and LHβ expression in the pituitary differs among grouper species with the same pituitary structure, suggesting that the roles of both hormones may be different between species.
In 2017, field experiments were performed to examine the effect of laver density in laver culture nets on yield-related traits, such as laver thallus length and dried laver quality. Thallus length under high-density conditions was significantly shorter and harvest weight was lower than those under normal-density and low-density conditions. Free amino acid, such as glutamic acid, content was significantly inversely related with laver density. The number of chewing strokes needed to masticate dried laver produced under high-density conditions was greater than that needed for low-density dried laver. The results obtained in the present study suggest that yield and quality traits, such as tasting scores of dried laver, are significantly inversely related with laver culture density.
Online survey data collected from 500 males and 500 females aged 15 to 79 years in Japan were used to assess public awareness and recognition of Japanʼs inland fishery cooperatives. Approximately 60% of respondents were aware of the existence of inland fishery cooperatives in Japan. The proportion of aware individuals was higher among older people and male respondents. Many respondents had a favorable impression of Japanʼs inland fishery cooperatives and felt that cooperatives should continue to exist. Main reasons that respondents felt that Japanʼs inland fishery cooperatives should exist were as follows: “ the cooperatives manage fishery resources ” and “ the cooperatives conserve river and lake environments ”. However, many older male respondents were opposed to the existence of cooperatives. Main reasons that respondents felt that Japanʼs inland fishery cooperatives should not exist were as follows: “ the cooperatives insist on vested rights ”, “ the cooperatives monopolize the rivers and lakes ” and “ the cooperatives think only about themselves ”.
To evaluate suitable salinity conditions for culturing Rhodomonas sp. (Hf-1 strain), the effect of different salinities on the growth and biochemical compositions were studied. A series of culture trials were carried out at five different salinity levels (7, 14, 21, 28, 35 psu) for a period of nine days to investigate the effects on algal growth, fatty acid composition, amount of protein and fatty acids by biochemical analyses. Regarding results, stable algal growths were observed in each salinity group, except at 7 psu. Moreover, among 14 to 35 psu groups, no significant differences were observed in the amount of essential fatty acids, EPA/DHA ratios, and protein contents. Based upon these results, it could be suggested that the present microalga can be cultured under a wide range of salinity conditions without impairing the high EPA and DHA contents and is suitable as a feed organism used in the seedling production of marine animals.
We evaluated vulnerability of pelagic larvae and early settled juveniles in Manila clam Ruditapes philippinarum to various invertebrate predators. Predation trials in laboratory revealed that moon jellyfish Aurelia sp. and oyster Crassostrea gigas prey upon the pelagic larvae of clam. We also found that grass shrimp Palaemon serrifer, Xanthidae crab Leptodius exaratus, subtropical pebble crab Gaetice depressus, sea cucumber Apostichopus japonicus and hermit crab Pagurus minutus feed on clam juveniles, and that P. serrifer and P. minutus consume > 90 clam juveniles within 24 h. Manila clam in the early life stage are thus highly vulnerable to various predators.
We evaluated the protection against viral challenge afforded to oblong rockfish Sebastes oblongus by vaccination with formalin-inactivated VHS virus. The cumulative mortalities in the fish that received the vaccine at 12°C and 20°C were significantly lower than those in the control fish given PBS at the same temperatures (P < 0.01). The relative percentage survival of all the vaccinated fish was 100%. Therefore, immunization with the formalin-inactivated vaccine at both 20°C and 12°C provided significant protection to oblong rockfish against VHS. This is the first report of an efficient vaccine against VHS in the oblong rockfish.
Survival rates of Ayu larvae reared at conditions of several different food densities in a tank for 15 days were studied. The study showed mean larval survival rates of 41-51, 53-57 and 5-6 percent for the larvae respectively fed on 10.0, 1.0 and 0.1 rotifers per milliliter. The survival rate of larvae being fed on 0.1 rotifers / ml was significantly lower than the others. These results suggest an unfavorable influence in the number of Ayu juveniles migrating back to rivers when food quantity in the brackish water area near the coast falls near to 0.1 zooplankton per milliliter level.