Aquaculture Research

In recirculating aquaculture systems (RAS), off-flavors can accumulate in fish muscle tissue. They are problematic for consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, the study of off-flavors in fish focused on muddy and earthy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB), but other unwanted flavors and compounds have also been identified. In this study, the selected off-flavors were chemically quantified in fish from a RAS-rearing rainbow trout (Oncorhynchus mykiss) and in different stages of depuration. A group of trained panelists with experience in sensory evaluation was specifically trained in analyzing rainbow trout samples. The panelists evaluated the fish with a sensory profile of 29 sensory attributes (12 odor, 5 taste, and 12 flavor properties). Overall, the concentrations of all the studied off-flavor compounds decreased, some to below the limit of detection and others (e.g., octanal, octanoic acid, phenylacetaldehyde, and acetoin) to a certain low level. Moldy, earthy, and musty odors and flavors especially decreased during depuration compared to fish in RAS. This study shows the consistency of the chemical analysis and sensory profiling. It also provides important information about the effects of the depuration period in RAS and on the chemical and sensorial quality of rainbow trout.

Sex-reversed females are the fathers of all-female fish and their sperm quality directly affects the quality of all-female fish. In this study, fecundity, physiological characteristics, biochemical characteristics, ultrastructure, and viability of sex-reversed female sperm after cryopreservation were investigated to understand sperm quality. (1) The sex-reversed female sperm had a lower fertilization rate, hatching rate, and larval survival rate of 72 hr and higher larval deformation rate compared with normal male sperm. (2) The changes in activation rate between normal male and sex-reversed female sperm under different salinity and pH conditions were the same; the optimum salinity was between 0 and 4%, and the optimum pH was 5.5. (3) The preservation time of sex-reversed female sperm is significantly shorter than that of normal male sperm at room temperature. (4) Sex-reversed female sperm had lower ATPase content and c/p value than normal male sperm. (5) Ultrastructural injury including damaged membranes of the head and mitochondria, broken flagella, greater mitochondrial damage, and mitochondrial membrane expansion were found in the sex-reversed female sperm. (6) The most suitable antifreeze for cryopreservation of sex-reversed female and normal male sperm was 10% ethylene glycol and dilution was D-15, but the activation rate, movement, and life span of sex-reversed female sperm were reduced after cryopreservation. It was speculated that the sperm mitochondria of the sex-reversed female were more damaged than those of the normal male, which led to differences in fertility and cryopreservation.

Six different feeding regimes (FR) were tested from 7 to 38 days post hatching (dph). Five thousand four hundred larvae (7 dph, 0.048 g) were randomly stocked in 18 fiberglass tanks contained 100 L fresh water (300 larvae per each tank). In larvae fed with FR-B, includes Artemia nauplii (AN) + Artemia biomass (AB) + microdiet (MD), the body weight (BW) at the end of trail (38 dph) similar the FR-D (AN + CHL + AB + MD), and E (AN + CHL + AB), was at high level. Survival rate was higher in larvae fed FR-A includes AN + chironomid larvae (CHL) + MD, but had a lower BW (). Moderate BW and survival rate were detected in larvae fed FR-C (AN + DP + MD). Larvae fed only MD (FR-F), had the lowest survival and the highest BW (). Different FR had a significant effect on crude protein (CP), crude fat (CF), ash, and dry weight (). The larvae fed FR-C and D had the highest CP (). The highest CF and ash in larvae were detected in FR-F and C, respectively (). Larvae from FR-A and B had higher levels of n−3 long chain polyunsaturated fatty acids in comparison with others FR (). The use of AB and CHL can increased the weight and survival rate of larvae, respectively. At the end of trail, the activity of pepsin, trypsin, lipase and α-amylase enzyme levels were lower in FR-B and F than others FR. Totally, by using a combination of AN + CHL + AB + MD had better results than others and ordered to H. huso larvae feeding. Using MD alone, can cause lesser development of the digestive system and little attractiveness, therefore it can cause starvation, and the empty digestive tract of larvae.

In this study, the complete cDNA sequence (1552 bp) of the cold-inducible RNA binding protein gene (cirbp gene) was successfully cloned from the liver in Acanthopagrus schlegelii (initial weight: 15.0 ± 2.3 g). Results showed that Ascirbp (cirbp gene from A. schlegelii) gene has 24 phosphorylation sites, no signal peptide, and no transmembrane helix structure. AsCIRBP, with a molecular weight of 18.84 ku and an isoelectric point of 9.04 was a stable protein that encodes 182 amino acids. Subcellular localization analysis of this protein showed that it was located in the nucleus. Sequence alignment results showed that the AsCIRBP amino acid sequences of various fishes including black porgy were highly conserved, especially the RNA recognition motif (RRM). Those results of real-time quantitative PCR (qRT-PCR) demonstrated that Ascirbp gene was specifically expressed in the liver tissue of black porgy and its expression was significantly increased under cold stress or cold acclimation. The RNA interference experiment results showed that Ascirbp-dsRNA could suppress the expression of Ascirbp gene in the liver of black porgy through intraperitoneal injection. After silencing the expression of Ascirbp gene, RNAi groups were more severely damaged in the structure of the liver tissue and more prone to apoptosis under cold stress than control groups. The results of the study on the linkage between Ascirbp gene expression and mitochondrial apoptosis pathways showed that changes in the expression of the Ascirbp gene had a significant effect on the expression of key genes of apoptosis. The most striking result from silencing the expression of the Ascirbp gene was that expressions of the bcl-2 and apaf-1 gene in the liver of black porgy decreased significantly, which can block the normal apoptotic process. After the disruption of the normal apoptotic process, the expressions of p53, bax, cyto-c, caspase-9, caspase-3, diablo, and caspase-1 gene were significantly affected. These results suggest that Ascirbp gene can inhibit apoptosis and protect tissue structure in the liver tissue of black porgy at low temperatures.

In Ghana, aquaculture offers acceptable opportunities for generating income. Cage aquaculture has a lot of potential for growth in Lake Volta. In this region, cage aquaculture farmers perform aquaculture in a variety of ways that fall into three major groups: commercial, medium scale, and small scale. In this study, the profitability and production economics of small-scale aquaculture operations in Lake Volta were examined. The average total revenue accrued and the average total costs of production were Gh₵395231.25 and Gh₵267970.15, respectively. The overall gross margin and net return for all the farms were Gh₵130294.02 and Gh₵127,261.10 per cycle, respectively. The overall assessment of the profitability performance indicators such as the benefit-cost ratio (BCR), the return on investment (ROI), the net present value (NPV), the operating expense ratio (OE), the operating profit margin (OPM), and the gross margin ratio (GMR) were 1.47, 47.49%, Gh₵407625.47, 0.77%, 32.20%, and 33.00%, respectively. These indicators showed that small-scale cage fish farming in the study area is profitable. The sensitivity analysis further demonstrated that small-scale cage fish production was robustly profitable. In light of this, the study suggests that stakeholders educate small-scale cage aquaculture farmers on the profitability of the business and make a concerted effort to teach and equip farmers with best management practises (BMPs), water quality management, feeds, and feeding management.

Melanoma differentiation-associated gene 5 (MDA5) and the laboratory of genetics and physiology 2 (LGP2) are family members of retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), which play important roles in the immune response against pathogens invasion. In the present study, MDA5 and LGP2 genes were identified in largemouth bass (Micropterus salmoides), a fish species with a great economic value. The two proteins contained similar conserved domains and motifs as their counterparts of other vertebrates, including the DExDc domain (the DEAD/DEAH box helicases domain), HELICc domain (helicases superfamily domain), and regulatory domain (RD). Real-time qPCR revealed that the two genes were constitutively expressed in tissues of healthy fish and could be induced in the spleen by polyinosinic and polycytidylic acid (polyI:C) challenge in vivo. Also, selective pressure analysis revealed that the negative selection had roles in the evolutions of the two genes. Furthermore, the dsRNA binding mechanism of msLGP2 and msMDA5 were analyzed by the molecular docking strategy. The amino acids of msLGP2 involved in dsRNA binding were V604, N663, L682, and L684, which were located in the regulatory domain (RD) of msLGP2. The amino acids of msMDA5 involved in dsRNA binding were G429, H434, L842, and L845, which were located in the DExDc domain and the RD domain of msMDA5. These results indicated that fish LGP2 and MDA5 might share similar functions and ligand binding mechanism as their mammalian counterparts.