Optimization Effects Of Arachidonic Acid (ARA) On Ovarian Development And Reproductive Performance Of Female Breeder Cherax Quadricarinatus

As a globally significant economic crustacean, the quality of seedlings and reproductive efficiency of Cherax quadricarinatus are critical bottlenecks limiting industry development. A study published in 2025 in Aquaculture (DOI: 10.1016/j.aquaculture.2025.742358) systematically revealed the crucial role of arachidonic acid (ARA) in regulating ovarian maturity, lipid metabolism, and hormone synthesis in breeders, providing important scientific evidence for optimizing broodstock feed formulations and enhancing reproductive performance.

I. Research Background and Experimental Design

(1) Industry Challenges and Scientific Issues

C. quadricarinatus has characteristics of batch spawning and yolk nutrition dependence, with the nutritional status of breeders directly determining egg quality and juvenile survival rates. However, there is currently a lack of specialized feeds targeting their reproductive stages, especially regarding fatty acid nutritional requirements. As an essential n-6 polyunsaturated fatty acid (HUFA) for aquatic animals, ARA plays a dual role in gonadal development: appropriate supplementation can promote oocyte maturation, but excess may cause oxidative stress. This study aims to determine the optimal addition level of ARA in broodstock feed and its mechanism of action.

(2) Experimental Methods

- Feed Design: Five groups of equal nitrogen (39% protein) and equal fat (9% fat) feeds were formulated, with ARA addition levels of 0% (control), 0.6%, 1.2%, 1.8%, and 2.4%, using soybean oil to make up for fat differences.

- Experimental Subjects: Female breeders weighing 52.14±0.25 g were selected, with a breeding cycle of 10 weeks, evaluating ovarian development and reproductive performance at weeks 6 and 10.

- Detection Indicators:

- Growth and Reproduction: Survival rate, weight gain rate (WG), hepatosomatic index (HSI), spawning quantity, egg nutrient composition.

- Physiological Mechanisms: Serum sex hormones (progesterone, 17β-estradiol, farnesyl methyl ester), ovarian histology (yolk granule deposition, oocyte maturation), lipid metabolism (cholesterol, triglyceride transport), metabolomics (ARA metabolic pathway and prostaglandin levels).

II. Key Research Findings

(1) Promotion of Ovarian Development by ARA

- Gonadosomatic Index and Hormonal Regulation: The gonadosomatic index (GSI) of breeders in the 1.8% ARA group was significantly higher than that of the control group (p<0.05). Progesterone and 17β-estradiol levels increased by 42% and 35%, respectively, indicating that ARA accelerates ovarian maturation by enhancing steroid hormone synthesis. Notably, the highest levels of farnesyl methyl ester (a precursor to crustacean molting hormones) were found in the control group, suggesting that high concentrations of ARA may inhibit molting-related hormones, specifically promoting reproductive development.

- Histological Evidence: In the 1.8% ARA group, the proportion of mature oocytes in the ovary reached 65%, significantly higher than 32% in the control group, with a 58% increase in yolk granule deposition. However, excessive follicular cell proliferation was observed in the 2.4% ARA group, possibly due to inflammation caused by excess ARA, leading to developmental obstruction.

(2) Regulation of Lipid Metabolism and Nutrient Deposition

- Hepatopancreas-Ovary Lipid Transport: ARA significantly enhances the efficiency of total cholesterol and triglyceride transport from the hepatopancreas to the ovary. The lipid content in the hepatopancreas of the 1.8% ARA group decreased by 22% compared to the control group, while ovarian lipid content increased by 39%, indicating that ARA optimizes nutrient distribution by activating lipid transport proteins (such as apolipoproteins).

- Egg Fatty Acid Composition: With increasing levels of ARA in the diet, the ARA content in eggs showed a dose-dependent increase (1.2% in the control group vs. 3.1% in the 1.8% group), while optimizing the n-6/n-3 fatty acid ratio, which is beneficial for early embryonic energy supply and cell membrane stability.

(3) Molecular Mechanisms Revealed by Metabolomics

Serum metabolomic analysis showed that the ARA metabolic pathway was significantly upregulated in the 1.8% ARA group, with prostaglandin E₂ (PGE₂), F₂α (PGF₂α), and 14,15-deoxy-Δ12,14-PGJ₂ levels increasing by 2.3 times, 1.8 times, and 1.5 times, respectively. These active metabolites function through the following pathways:

- PGs-mediated signaling pathways: PGE₂ promotes oocyte meiotic maturation, and PGF₂α induces ovulation-related muscle contractions.

- Neuro-endocrine interactions: Activation of neuroactive ligand-receptor pathways synergistically regulates the release of gonadotropins, enhancing the sensitivity of the ovary to hormonal signals.

III. Dose-effect Relationship and Optimal Levels for Reproductive Performance

(1) Spawning Quantity and Egg Quality

The single spawning quantity of breeders in the 1.8% ARA group reached (285±18) eggs, an increase of 48% compared to the control group (192±15 eggs), with a 21% increase in fertilized egg hatching rates. Protein, total lipids, and essential amino acids in eggs increased first and then decreased with increasing ARA levels, reaching a peak in the 1.8% group, indicating that appropriate ARA levels enhance yolk substance accumulation.

(2) Determination of Optimal ARA Addition Levels

Through quadratic regression analysis, combining GSI, spawning quantity, and hormone levels, the optimal addition range of ARA in female C. quadricarinatus breeder feed was determined to be 1.675%-1.768%. Below this range, insufficient hormone synthesis leads to delayed maturation; above this range, ovarian tissue damage may occur due to oxidative stress.

IV. Research Significance and Application Prospects

(1) Theoretical Value

For the first time in crustaceans, it was confirmed that ARA regulates ovarian development through a "PGs-steroid hormones-lipid metabolism" axis involving three mechanisms, contributing to the theory of reproduction nutrition in aquatic animals. The discovery of antagonistic effects between farnesyl methyl ester and ARA provides new insights into understanding the interaction between reproduction and molting in crustaceans.

(2) Industrial Implications

- Optimization of Feed Formulations: It is recommended to add approximately 1.7% ARA to the feed of C. quadricarinatus breeders, potentially using fish oils rich in ARA (such as squid oil) combined with soybean oil to balance cost and efficacy.

- Precision Farming Management: Dynamically adjust ARA supply according to the ovarian development stage of breeders, reinforcing supplementation during vitellogenesis (2-3 weeks before spawning) to improve the synchronization of spawning and the efficiency of mass production of juveniles.

- Sustainable Farming Directions: Reduce dependence on traditional fishmeal in feeds by partially replacing animal fats with plant-based ARA (such as fungal oils), reducing environmental pressure.

This study systematically elucidated the optimization effects and molecular mechanisms of ARA on the reproductive performance of C. quadricarinatus breeders, with findings applicable to other economically important crustaceans such as Litopenaeus vannamei and Scylla paramamosain. Future research should further explore the synergistic effects of ARA and n-3 HUFA (such as DHA), as well as the mediating role of gut microbiota in fatty acid metabolism, laying the foundation for building an integrated "nutrition-gut-reproduction" regulation model. As aquaculture moves towards intensification and refinement, precision nutrition technology based on fatty acids will become a core driving force for enhancing industrial competitiveness.

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Reference:

Optimal arachidonic acid supplementation enhances ovarian development and reproductive performance in female Redclaw crayfish (Cherax quadricarinatus) https://doi.org/10.1016/j.aquaculture.2025.742358