Digestive enzyme activity in the intestine of Nile tilapia (Oreochromis niloticus L.) under pond and cage farming systems

Protein hydrolysates derived from aquaculture and marine byproducts through autolytic hydrolysis

Autolysis technology has shown potential for protein hydrolysates production from marine and aquaculture byproducts. Viscera are a source of cheap proteolytic enzymes for producing protein hydrolysates from the whole fish or processing byproducts of the most valuable commercial species by applying autolysis technology. The use of autolysis allows economical production of protein hydrolysate and provides an opportunity to valorize downstream fish and shellfish processing byproducts at a lower cost. As a result, production and application of marine byproduct autolysates is increasing in the global protein hydrolysates market. Nevertheless, several restrictions occur with autolysis, including lipid and protein oxidation mediated by the heterogeneous composition of byproducts. The generally poor storage and handling of byproducts may increase the formation of undesirable metabolites during autolysis, which can be harmful. The formation of nitrogenous compounds (i.e., biogenic amines), loss of freshness, and process of autolysis in the byproducts could increase the rate of quality and safety loss and lead to more significant concern about the use of autolysates for human food applications. The current review focuses on the autolysis process, which is applied for the hydrolysis of aquaculture and marine discards to obtain peptides as functional or nutritive ingredients. It further addresses the latest findings on the mechanisms and factors contributing the deterioration of byproducts and possible ways to control oxidation and other food quality and safety issues in raw materials and protein hydrolysates.

Effective mechanisms of water purification for nitrogen-modified attapulgite, volcanic rock, and combined exogenous microorganisms

The study tested the water purification mechanism of the combination of microorganisms and purification materials via characteristic, enzymatic, and metagenomics methods. At 48 h, the removal rates of total nitrogen, total phosphorous, and Mn chemical oxygen demand in the combination group were 46.91, 50.93, and 65.08%, respectively. The alkaline phosphatase (AKP) activity increased during all times tested in the volcanic rock, Al@TCAP, and exogenous microorganism groups, while the organophosphorus hydrolase (OPH), dehydrogenase (DHO), and microbial nitrite reductase (NAR) activities increased at 36-48, 6-24, and 36-48 h, respectively. However, the tested activities only increased in the combination groups at 48 h. Al@TCAP exhibits a weak microbial loading capacity, and the Al@TCAP removal is primarily attributed to adsorption. The volcanic rock has a sufficient ability to load microorganisms, and the organisms primarily perform the removal for improved water quality. The predominant genera Pirellulaceae and Polynucleobacter served as the sensitive biomarkers for the treatment at 24, 36-48 h. Al@TCAP increased the expression of Planctomycetes and Actinobacteria, while volcanic rock increased and decreased the expression of Planctomycetes and Proteobacteria. The growth of Planctomycetes and the denitrification reaction were promoted by Al@TCAP and the exogenous microorganisms. The purification material addition group decreased the expression of Hyaloraphidium, Chytridiomycetes (especially Hyaloraphidium), and Monoblepharidomycetes and increased at 36-48 h, respectively. Ascomycota, Basidiomycota, and Kickxellomycota increased in group E, which enhanced the nitrogen cycle through microbial enzyme activities, and the growth of the genus Aspergillus enhanced the phosphorous purification effect.

The Effect of Adding Molasses in Different Times on Performance of Nile Tilapia (Oreochromis niloticus) Raised in a Low-Salinity Biofloc System

This study aimed to evaluate the effect of adding molasses in different times on water quality, growth performance, body biochemical composition, digestive and hepatic enzymes of Nile tilapia in the biofloc system. Tilapia fingerlings (1.53 ± 0.14 g) were distributed in five treatments including control, BFT24 (adding molasses to the tanks every 24 h), BFT48 (48 h), BFT72 (72 h), and BFT96 (96 h) and reared for 37 days in fiberglass tanks (130 L), with a stocking density of one fish per litre. The results showed that highest increases in biomass (740.12 g) and survival (98.97%) were obtained in BFT24 treatment (P<0.05). The body composition was affected by the experimental treatments so that the highest protein content was obtained in the BFT72 (P<0.05). Digestive enzymes activities were significantly (P<0.05) higher in BFT treatments than the control group. The current study showed higher biomass and survival ratio for Nile tilapia were observed in BFT24 treatment. The liver and digestive enzymes of Nile tilapia were affected by the different addition times of molasses to the rearing tanks.

Changes in digestive enzyme activities during the early ontogeny of the South American cichlid (Cichlasoma dimerus)

Cichlasoma dimerus is a neotropical cichlid that has been used as a biological model for neuroendocrinology studies. However, its culture is problematic in terms of larval feeding to allow having enough fry quantity and quality. Larviculture requires full knowledge about the digestive system and nutrition; therefore, this study was intended to assess the digestive enzymes' changes at different ages during the early ontogeny. Acid protease activity was detectable from the first day after hatching (dah), increasing to its maximum peaks on 9 dah. In contrast, alkaline proteases had low activity in the first days of life but reached their maximum activity on 17 dah. Chymotrypsin, L-aminopeptidase, and carboxypeptidase A activities increased at 6 dah, while trypsin activity was first detected on 13 dah and reached its maximum activity on 17 dah. Lipase and α-amylase activity were detectable at low levels in the first days of life, but the activity fluctuated and reaching its maximum activity at 21 dah. Alkaline phosphatase continued to oscillate and had two maximum activity peaks, the first at 6 dah and the second at 19 dah. Zymograms of alkaline proteases on day 6 dah six revealed four activity bands with molecular weights from 16.1 to 77.7 kDa. On 13 dah, two more activity bands of 24.4 and 121.9 kDa were detected, having a total of six proteases. The enzymatic activity analyzes indicate the digestive system shows the low activity of some enzymes in the first days after hatching, registering significant increases on 6 dah and the maximum peaks of activities around at 17 dah. Therefore, we recommend replacing live food with dry feed and only providing dry feed after day 17 dah.

A highly stable raw starch digesting α-amylase from Nile tilapia (Oreochromis niloticus) viscera

A raw starch digesting α-amylase from Nile tilapia (Oreochromis niloticus) intestine was identified. The α-amylase, AMY-T, had an estimated molecular weight of 60 kDa and purified to near homogeneity. AMY-T showed an apparent K_M 4.78 mg/mL and V_max 0.44 mg/mL/min) towards soluble starch. It was highly stable for 24 h in the pH range 3.0-10.0, and to solvents like methanol, isopropanol, butanol, dimethylformamide, DMSO and ethyl-ether. AMY-T was able to digest different carbohydrates, mainly showing endo-activity. Importantly, AMY-T was catalytically efficient and adsorbing towards raw potato starch at temperature documented for other raw starch digesting α-amylases. Thin layer and anion exchange chromatography characterization showed that the end products of raw starch hydrolysis were glucose, maltose and maltodextrins, with degree of polymerisation ranging 1-8. Scanning electron microscopy analysis of the AMY-T treated starch granules documented both granular exo- and endo-attack by AMY-T. These catalytic capabilities suggest high potential for AMY-T for industrial use.

Metabolic Effect of Dietary Taurine Supplementation on Grouper (Epinephelus coioides): A 1H-NMR-Based Metabolomics Study

Taurine is an indispensable amino acid for many fish species and taurine supplementation is needed when plant-based diets are used as the primary protein source for these species. However, there is limited information available to understand the physiological or metabolic effects of taurine on fish. In this study, ¹H nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted to identify the metabolic profile change in the fish intestine with the aim to assess the effect of dietary taurine supplementation on the physiological and metabolomic variation of fish, and reveal the possible mechanism of taurine's metabolic effect. Grouper (Epinephelus coioides) were divided into four groups and fed diets containing 0.0%, 0.5%, 1.0%, and 1.5% taurine supplementation for 84 days. After extraction using aqueous and organic solvents, 25 significant taurine-induced metabolic changes were identified. These metabolic changes in grouper intestine were characterized by differences in carbohydrate, amino acid, lipid and nucleotide. The results reflected both the physiological state and growth of the fish, and indicated that taurine supplementation significantly affects the metabolome of fish, improves energy utilization and amino acid uptake, promotes protein, lipid and purine synthesis, and accelerates fish growth.

Changes in digestive enzymes activities during the initial ontogeny of wolf cichlid, Parachromis dovii (Perciformes: Cichlidae)

ABSTRACT Wolf cichlid, Parachromis dovii, is a species with a high potential for aquaculture in Central America; however, the knowledge of the digestive physiology in larvae period is limited. For these reason, this study evaluated the changes on digestive enzymes (alkaline and acid proteases, trypsin, chymotrypsin, aminopeptidase, carboxypeptidase, lipases, amylases, and phosphatases) during early ontogeny by biochemical analysis. All digestive enzymes were detected at first feeding (6 days after hatching, DAH, 9.49 mm, 168 degree-days DD). Afterwards all enzymes reached two main peaks in activity at 14 or 22 DAH (15.10 mm, 364 DD and 20.83 mm, 550 DD, respectively). Later, there was a gradual decrease in activity for trypsin and acid and alkaline phosphatases until reach the lowest values at 41 DAH. In the case of acid proteases, chymotrypsin, aminopeptidase, carboxypeptidase, lipase and amylase, all activities reached their maximum values at the end of the larval period, except for alkaline proteases, which showed the maximum value at 14 DAH (15.10 mm, 364 DD). Parachromis dovii larvae have an early capability to hydrolyze exogenous food, agreeing with other carnivorous neotropical cichlid species, for this reason we proposed that the weaning process could begin at 14 DAH.

Aluminium sulfate exposure: A set of effects on hydrolases from brain, muscle and digestive tract of juvenile Nile tilapia (Oreochromis niloticus)

Aluminium is a major pollutant due to its constant disposal in aquatic environments through anthropogenic activities. The physiological effects of this metal in fish are still scarce in the literature. This study investigated the in vivo and in vitro effects of aluminium sulfate on the activity of enzymes from Nile tilapia (Oreochromis niloticus): brain acetylcholinesterase (AChE), muscle cholinesterases (AChE-like and BChE-like activities), pepsin, trypsin, chymotrypsin and amylase. Fish were in vivo exposed during 14days when the following experimental groups were assayed: control group (CG), exposure to Al₂(SO₄)₃ at 1μg·mL^-1 (G1) and 3μg·mL^-1 (G3) (concentrations compatible with the use of aluminium sulfate as coagulant in water treatment). In vitro exposure was performed using animals of CG treatment. Both in vivo and in vitro exposure increased cholinesterase activity in relation to controls. The highest cholinesterase activity was observed for muscle BChE-like enzyme in G3. In contrast, the digestive enzymes showed decreased activity in both in vivo and in vitro exposures. The highest inhibitory effect was observed for pepsin activity. The inhibition of serine proteases was also quantitatively analyzed in zymograms using pixel optical densitometry as area under the peaks (AUP) and integrated density (ID). These results suggest that the inhibition of digestive enzymes in combination with activation of cholinesterases in O. niloticus is a set of biochemical effects that evidence the presence of aluminium in the aquatic environment. Moreover, these enzymatic alterations may support further studies on physiological changes in this species with implications for its neurological and digestive metabolisms.