There is a need to enhance the availability of a larger range of tiny sized live feeds in order to diversify the number of species farmed within the marine fish trade. Copepod nauplii are a great choice of live feed before moving on to rotifers. However, their culture’s existing constraints must be overcome.
Assistant Professor
Mandapam Centre for Sustainable Aquaculture, TNJFU
INTRODUCTION
The demand for adequately sized live food as a first feed is the limiting element in the production of high value marine finfishes. This is related to the small gape size of several commercially important fish species. The scarcity of acceptable live feeds has caused a bottleneck in the production of marine fish species, and new developments are needed to allow for the expansion of this culture business. Ingestion, digestion, and assimilation of live prey are essential for the early life stages of marine animals. As a result, the utilisation of live feeds is crucial for the proper upbringing of juveniles of nearly all cultured species. Fish larvae find prey through movement, with neuromasts on their bodies detecting water motion and plankton frequencies and eyes recognising proper movement patterns. As a result, inert meals rarely stimulate fish larvae.
EXIGENCIES
Live feeds are the vital link between the cessation of endogenous yolk supply and post-metamorphosis, when gastric glands have grown and artificial diet digestion is possible. Formulated diets, on the other hand, can help juvenile fish grow quickly while also offering adequate nutritional contents at a lesser cost. Live food must be of appropriate size for the species and age to avoid poor larval growth. Rotifers are usually fed first, then Artemia nauplii, and lastly enriched Artemia as gape size grows. Currently grown marine finfishes can consume routinely used live feeds. While brine shrimp are particularly suitable to commercial culture, feeding rotifers has been noted to be problematic due to their tiny size, nutritional heterogeneity, and rotifer culture’s vulnerability to crashing. Although Artemia nauplii are extensively used as live food, it is far from the best live food organism in terms of nutritional requirements of fish/shrimp. The most significant disadvantages of Artemia are significant differences in cost, physical qualities, and nutritional quality among different sources. As a result, the production of very small, rapidly developing, and extremely sensitive larvae continues to be a bottleneck in the commercially viable culture of many marine fish species.
EMINENCES
Nutritional components such as n-3 fatty acids, essential amino acids (EAA), and protein content in live feeds are vital for larval finfish and crustaceans’ survival and growth. As a consequence, the development of copepods becomes increasingly important. Copepods are the most numerous creatures in marine habitats. Their nauplii are the natural food of most wild fish larvae, making copepod nauplii a better diet for rearing fish than rotifers or Artemia nauplii. Copepod nauplii are an appealing prey item for larval fish because their chaotic “zig-zag” motion which stimulates foraging animals. Copepod nauplii are also considered great live food because they do not require enrichment due to the high quantities of fatty acids in their diet. Marine copepods are regarded as “nutritionally superior live feeds” for commercially important cultivable species because they are a valuable source of protein, lipid (especially HUFA, 20:5 n3 and 22:6 n3), carbohydrates, and enzymes (amylase, protease, exonuclease, and esterase), all of which are required for larval survival, growth, digestion, and metamorphosis, and have a relatively high weight specific caloric content. Furthermore, the calanoids’ maturation stages from first nauplius to adult present a diverse range of prey sizes (80 to 900 μm in length and 3–5 μg in dry weight) which makes them a suitable prey for a wide variety of developing fish sizes.
ENCUMBRANCES
The advantages of raising marine fish using copepod nauplii are self-evident. Smaller nauplii, on the other hand, may be unable to maintain larger larvae once they reach a certain size. The appropriate copepod species should be chosen based on these facts. The biggest challenge they will have if they are approved by the mainstream aquaculture business is finding a practical use. A live culture is essential to ensure a consistent supply of nauplii. While captive-bred cultures typically have densities less than two adults or ten nauplii per millilitre, live cultures seldom have densities greater than two adults or ten nauplii per millilitre. Maintaining copepod densities in higher levels of culture, however, does not always result in increased output. Cultures should be kept at or below maximum density to maximise output.
Most copepods do better on phytoplankton than on other types of diet when farmed. Despite the fact that phytoplankton production is expensive and complex, use of rice bran can be a cheap and good diet for smaller facilities. The long-term viability of prepared algae diets is unclear. Continuous breeding of the top performing individuals from cultures fed prepared diets could be used to create resistant copepod strains. As a result of selective breeding, less complex copepods would be more appealing to aquaculture operations.
The removal of nauplii from the culture is a time-consuming process. Although sieving can be used to harvest cyclopoid and calanoid nauplii, it is difficult and time consuming for harpacticoids, which have nauplii living in close proximity to adults. The extra labour is noticeable when compared to rotifer or Artemia nauplii harvesting methods that feed the entire population. The removal of the nauplii alone may have an effect on the culture’s population dynamics. Overharvesting is likely to reduce the population, potentially leading to a crash. This technique may be optimised in a controlled abiotic setting with a known population. It may enable for optimum harvest while preserving the culture’s integrity. The precise parameters of such a system, however, are unknown.
Copepod cultures are vulnerable to contamination. Although copepod species can dominate wild zooplankton populations, contamination in hatcheries is a severe concern. Copepod cultures are not only prone to ciliate infestations, but they are also commonly contaminated by rotifer species, which are likely kept on site. Copepod cultures are unlikely to out-compete invaders such as ciliates since they devour available food quickly.
CONCLUSION
There is a need to enhance the availability of a larger range of tiny sized live feeds in order to diversify the number of species farmed within the marine fish trade. Copepod nauplii are a great choice of live feed before moving on to rotifers. However, their culture’s existing constraints must be overcome. As a conclusion, focus should be given to the innovations required to overcome the bottlenecks now present in the commercial ornamental fish aquaculture trade.
References are available on request.
About R. Dinesh
Dinesh has been an Assistant Professor in the Department of Aquaculture at the Mandapam Centre for Sustainable Aquaculture (MCeSA) of Tamil Nadu Dr.J. Jayalalithaa Fisheries University (TNJFU), India since 2021. He undertakes strategic and applied research in the field of Mariculture, offering extension services to farmers as well. Dinesh completed his Master’s degree in Fisheries Science with a special focus on Aquaculture at the Central Institute of Fisheries Education (CIFE) and his undergraduate studies at TNJFU. His research interests lie in Aquaculture and Aquaculture Nutrition. Before joining academics, he was directly involved with the shrimp production industry for five years as a Technical officer and Aqua feed formulator, working with different corporates. He has won prestigious awards and has authored several books and peer-reviewed articles. Dinesh serves as a reviewer for high-impact journals, and he’s a member of various professional and academic societies.
