Microorganisms in Fish Feeds, Technological Innovations, and Key Strategies for Sustainable Aquaculture

The current status and development forecasts of vaccines for aquaculture and its effects on bacterial and viral diseases

The aquaculture sector predicts protein-rich meals by 2040 and has experienced significant economic shifts since 2000. However, challenges emanating from disease control measures, brood stock improvement, feed advancements, hatchery technology, and water quality management due to environmental fluctuations have been taken as major causative agents for hindering the sector's growth. For the past years, aquatic disease prevention and control have principally depended on the use of various antibiotics, ecologically integrated control, other immunoprophylaxis mechanisms, and chemical drugs, but the long-term use of chemicals such as antibiotics not only escalates antibiotic-resistant bacteria and genes but also harms the fish and the environments, resulting in drug residues in aquatic products, severely obstructing the growth of the aquaculture sector. The field of science has opened new avenues in basic and applied research for creating and producing innovative and effective vaccines and the enhancement of current vaccines to protect against numerous infectious diseases. Recent advances in vaccines and vaccinology could lead to novel vaccine candidates that can tackle fish diseases, including parasitic organism agents, for which the current vaccinations are inadequate. In this review, we study and evaluate the growing aquaculture production by focusing on the current knowledge, recent progress, and prospects related to vaccinations and immunizations in the aquaculture industry and their effects on treating bacterial and viral diseases. The subject matter covers a variety of vaccines, such as conventional inactivated and attenuated vaccines as well as advanced vaccines, and examines their importance in real-world aquaculture scenarios. To encourage enhanced importation of vaccines for aquaculture sustainability and profitability and also help in dealing with challenges emanating from diseases, national and international scientific and policy initiatives need to be informed about the fundamental understanding of vaccines.

Feeding global aquaculture

The growth of animal aquaculture requires ever more feed. Yet, fish and crustacean farming is argued to be sustainable because wild fish use is low and has improved over time. Here, accounting for trimmings and by-products from wild fish in aquaculture feed, and using four different sources of industry-reported feed composition data, we find ratios of fish inputs to farmed outputs of 0.36 to 1.15-27 to 307% higher than a previous estimate of 0.28. Furthermore, a metric that incorporates wild fish mortality during capture and excludes unfed systems raises the wild fish mortality-to-farmed fish output ratio to 0.57 to 1.78. We also evaluate terrestrial ingredients in aquaculture feeds. Widely cited estimates of declines in wild fish use from 1997 to 2017 entailed a trade-off of more than fivefold increase in feed crops over the same period. Our assessment challenges the sustainability of fed aquaculture and its role in food security.

The Escalating threat of climate change-driven diseases in fish: Evidence from a global perspective - A literature review

Climate change has brought significant alterations to the aquatic environment, leading to the rapid spread of infectious fish diseases with increasing water temperatures. It is crucial to understand how aquatic pathogens will impact fish in the context of climate change. This study aimed to assess the effects of climate change on fish diseases globally. Data from 104 papers published between 2003 and 2022 were analyzed to identify recent trends in the field. The majority of the studies (54%) focused on parasites, particularly proliferative kidney disease, while 22% examined bacteria. The United States accounted for 19% of the studies, followed by Canada at 14%, covering a wide range of fish species. More research was published on farmed fish (54%) than wild fish (30%), with a higher emphasis on freshwater species (62%) compared to marine species (34%). Most published studies (64%) focused on the local environment rather than the farm level (7%). The findings highlight temperature as a significant threat to global aquaculture and fisheries, impacting the progression of fish diseases. These impacts could be exacerbated by factors such as pH, salinity, and ocean acidification, posing challenges to fish health. Therefore, there is a pressing need for enhanced research and management strategies to address these issues effectively in the future.

Towards cleaner environment: recycling microalgal co-product to reduce emissions and impacts while eliminating fishmeal in rainbow trout feed for sustainable aquaculture

The rapid increase in aquaculture over the last several decades has led to concerns about the environmental impact of fish feeds relying on marine resources for fishmeal (FM). We aim to assess Nannochloropsis sp. QH25 co-product as a viable and sustainable replacement for FM in juvenile rainbow trout, Oncorhynchus mykiss, feeds. We formulated four experimental diets: a reference (FM based), 33N, 66N, and 100N diet (33%, 66%, and 100% co-product replacement). Rainbow trout were randomly assigned to one of 16 tanks and randomly assigned an experimental diet to consume throughout the experiment (64 days total), with four replicate tanks per diet. We compared the phosphorus (P) and nitrogen (N) digestibility, emissions, and growth between diets and, compared six environmental impacts (biotic resource use (BRU), global warming potential (GWP), water use, land use, marine eutrophication potential (MEP), and freshwater eutrophication potential (FEP)) of each diet. Our results indicate that replacing FM with co-product did not significantly alter growth. P digestibility of the experimental and reference diets was comparable. BRU conversion ratio was significantly lower in the experimental diets. However, there were significantly higher water and land use conversion ratios but insignificantly higher results in GWP, MEP, and FEP between the reference and 100N diet.

Combined Effects of Yellow Mealworm (Tenebrio molitor) and Saccharomyces cerevisiae on the Growth Performance, Feed Utilization Intestinal Health, and Blood Biomarkers of Nile Tilapia (Oreochromis niloticus) Fed Fish Meal-Free Diets

Aquafeed quality is the most critical factor for aquaculture sustainability. However, limitations of traditional feed ingredients such as fishmeal (FM) need alternative strategies to ensure the nutritional requirements for aquatic animals. In this trial, four test diets were formulated (2 × 2 factorial design), where FM was incorporated in two diets at 10% with or without Saccharomyces cerevisiae (SC) at 1 g/kg. At the same time, FM was replaced with yellow mealworm (Tenebrio molitor) meal (TM) with or without SC at 1 g/kg. The growth performance indices (final weight, weight gain, and SGR), and the feed utilization indices (FCR and PER) were markedly affected by the protein source (FM or TM) and dietary SC (P < 0.05). The protein source (FM or TM) significantly (P < 0.05) affected the whole-body protein and lipid contents, while the moisture and ash contents were unaffected (P > 0.05) by TM or SC. The growth of the intestinal villi showed a marked increase in both height and branching in the treated groups with SC along the whole length of the intestine. Furthermore, the immune cell infiltration was prominent near the intestinal crypts of the middle intestinal segments in the supplemented groups by SC. Dietary TM and SC revealed improved hepatic parenchyma in the liver tissue better than other groups. The hematological indices, including hemoglobulin, hematocrit, red blood cells, and white blood cells, were markedly affected by dietary SC (P < 0.05). The lysozyme activity and phagocytic index were markedly affected by dietary SC, while phagocytic activity was affected by dietary TM (P < 0.05). The catalase, glutathione peroxidase, and malondialdehyde were markedly affected by the interaction between dietary protein source and SC, while superoxide dismutase was affected by dietary SC (P < 0.05). In conclusion, adding SC could enhance the utilization of TM by Nile tilapia with positive effects on the intestinal and liver histological features and the immune and antioxidative responses.