Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.

The Philippines is one of the significant contributors to world fisheries. In 2018, the total production from three sectors, e.g., aquaculture, municipal, and commercial fisheries, was about 4.36 million MT. With this, the Philippines ranked 13th as the top fish-producing country and placed 4th as the major seaweed producer worldwide. The total export earnings of the country from the fisheries sector was US$1.6 billion. The Philippine fisheries sector is an essential contributor to the national economy, providing income from foreign exchange and livelihood sources to almost 2 million Filipino fisherfolks. This review aimed to provide an overview of fisheries and aquaculture in the Philippines.

Fish protein hydrolysate (FPH) is the enzymatic hydrolysis of protein into smaller peptide and free amino acids, which has recently captured considerable attention as a supplementary ingredient in the aqua-feed industry sector. The present research aimed to observe the physiological, biochemical, and bacteriological study of FPH-treated diets and its effects on growth, hematology, plasma biochemistry, liver and gut histopathology, and resistance to Aeromonas hydrophila infection in Pabda (Ompok pabda). Four experimental diets (35% crude protein) were formulated with graded FPH supplementation (0, 0.5, 1, and 2%). The feed physiological parameters such as expansion ratio, bulk density, water stability, and floatability were not significantly affected by dietary FPH levels (p > 0.05), except for the pellet durability index (PDI). Furthermore, the diets with 1% and 2% FPH were more palatable to fish than other treatment diets. The total bacteria (TB) in fish diets and guts followed an increasing trend with the increase in various levels of FPH in diets. The significantly highest body weight, specific growth rate (SGR), total biomass (TB), survival rate (SR), condition factor (CF), and hepatosomatic index (HSI) were noted in 2% FPH-fed fish when compared with other treatment groups (p < 0.05). The feed intake of fish was significantly increased when increasing the FPH in diets (p < 0.05). The fish fed with a 2% FPH diet had significantly higher neutrophil, monocyte, lymphocyte, red blood cell, and platelet levels (p < 0.05). The blood glucose, creatinine, total protein, and globulin were significantly lower in control fish compared to other treatment groups (p < 0.05). The histopathological observation of mid intestine tissues displayed that 2% of FPH-diet-fed fish had a well-anchored epithelial wall with well-arranged goblet cells, a long villus structure, stratum compactum, and tunica muscularis compared to other treatments of FPH. The inclusion of FPH in diets up to 2% significantly improved the liver health of fish. The fish fed with 2% FPH had a significantly lower cumulative percent mortality (16.67%) against A. hydrophila infection in the bacterial challenge test (p < 0.05). Therefore, the present results suggested that using 2% FPH in the aqua-feed industry improves the growth performance, health status, and disease resistance of Pabda fingerlings in captivity.

Kappaphycus spp. and Eucheuma spp. are two economically significant seaweed species cultivated globally due to their carrageenan content with numerous commercial applications. They are mainly cultivated in the Philippines, Indonesia, Malaysia, and Tanzania. The culture of these seaweeds also provides income sources for many coastal dwellers. In 2018, the total global production from these seaweeds was about 11 million tonnes. One of the primary problems that affect seaweed production is the incidence of ice-ice disease. In this article, we reviewed the reported scientific journals on the ice-ice disease of two commercially cultured seaweed species (Kappaphycus spp. and Eucheuma spp.), focusing mainly on causes, occurrence, and control measures. The ice-ice disease is caused by both abiotic and biotic factors manifested by the presence of white and soft parts in the infected seaweeds. The occurrence of this disease varies from species, places, and seasons. Control measures may include proper farm management, polyculture with other seaweeds, pre-soaking with antibacterial substances and nutrient enrichment before out-planting, and possibly using genetic engineering.

Probiotics are gaining popularity both empirically and scientifically as eco-friendly alternatives in aquaculture. The present research proposed to examine the influences of selective probiotics on the growth, hematology, microbes, and morphology of the intestine of stinging catfish (Heteropneustes fossilis) in a biofloc system. Additionally, this study evaluated the benefit–cost ratio (BCR) of specific probiotics used in the biofloc system. Stinging catfish fingerlings (average weight 0.86 ± 0.26 g) were equally distributed (250 fingerlings/400 L water-filled PVC tank) into three treatment groups and reared for 16 weeks. Two commercial probiotics (CP-1 and CP-2) and one laboratory-developed probiotic were used in the study. The results showed significantly higher growth (weight gain and specific growth rate), feed efficiency, improved intestinal microbiota, and enhanced morphology in fish reared with laboratory-developed probiotics in the biofloc system. Moreover, indicators of increased immune responses, such as enhancements in the intestinal mucosal fold, width of enterocytes and lamina propria, and abundance of goblet cells, were also observed in fish reared with laboratory-developed probiotics. The BCR, which determined business profitability, was also highest for the laboratory-developed probiotics in the biofloc system. Therefore, the results suggest that laboratory-developed probiotics are economically viable and environmentally friendly growth stimulators for stinging catfish culture in a biofloc system.

The Philippines, being positioned in the center of the coral triangle, is among the major-fish producing countries globally. However, in many parts of the country, illegal fishing is rampant, particularly destructive fishing practices (DFPs). Fisheries involving DFPs cause direct ecological damage to the corals. These fishing activities threaten both natural habitats and aquatic resources. In this review paper, we reviewed available scientific literature reporting the DFPs in the Philippines from 1979 to 2022. Results revealed that most DFPs, such as dynamite fishing, cyanide fishing, and muro-ami fishing, were prevalent and remained a lingering problem in the Philippines from the 1930s up to this date. The weak enforcement of the existing laws and regulations fuels these activities, compromising the productive coral reef areas in the Philippines. Thus, it is urgently necessary to cease these DFPs as well as protect the integrity of vital and fragile ecosystems. It is therefore recommended that strict implementation of the laws and regulations at local and national levels is likely to stop or if not least, reduce the pressing issues of destructive fishing techniques.