Path Analysis and Multiple Linear Regression Fitting Study on Body Weight and Visceral Organ Mass of Male and Female Ussuri Catfish (Pseudobagras ussuriensis)

Abstract

Pseudobagras ussuriensis is a valuable freshwater fish species with enormous breeding potential. To clarify the relationship between the main visceral indices and body weight in this species, 139 cultured individuals were randomly selected to measure body weight and six major organs (namely the intestine, liver, swim bladder, kidney, spleen, and gonadal), and then the causal network of internal organs and body weight of one-year-old P. ussuriensis was analyzed by path analysis, and sex-specific regression models were developed. The results showed that the correlations between body weight and the masses of the intestine, liver, swim bladder, kidney, and gonad were significant, while the spleen mass showed a significant positive correlation with body weight. Path analysis revealed that the direct path coefficients of the intestine, liver, swim bladder, kidney, and gonad on body weight were significant, and that of the spleen was significant. Through regression analysis, multiple linear regression equations were established. Importantly, the swim bladder had the greatest direct effect on body weight in males, whereas the intestine exhibited the strongest direct effect in females. These findings provide valuable insights for the selection and breeding of P. ussuriensis based on visceral indices.

1. Introduction

Ussuri Catfish (Pseudobagrus ussuriensis), belonging to Siluriformes, Bagridae, Pseudobagrus, is an important freshwater economic species naturally distributed in Heilongjiang, Wusuli River, Nenjiang, Songhua River, the Pearl River, Hongze Lake, the Taihu Lake, and other water systems in China [1]. In the current context of China’s freshwater aquaculture industry seeking variety diversification and efficiency improvement, the breeding potential of Wusuli catfish is becoming increasingly prominent. It has core advantages such as rapid growth, strong disease resistance, tender meat, and unique flavor, perfectly meeting the growing demand of modern consumers for high-quality and characteristic aquatic products [2,3]. With the shrinking profit margins of traditional large-scale aquaculture species such as grass carp and carp, exploring and promoting high-value characteristic fish such as the Wusuli catfish has become one of the important directions for industry transformation and upgrading. The market value of Wusuli catfish is significant, with wild resources selling for up to 180 yuan/kg due to their rarity and preciousness. The price of large-scale aquaculture products in ponds remains stable at 80–90 yuan/kg, with broad profit margins and outstanding economic benefits. In recent years, its excellent breeding cost-effectiveness has attracted widespread attention in aquaculture, especially in response to its significant growth gender dimorphism (male growth rate is much higher than female), where male fish that mature during the same growth period weigh 2–3 times more than female fish [4,5]. Therefore, strengthening breeding work for the key economic trait of “weight” and analyzing its inherent relationship with physiological functions (such as visceral organ development) is crucial for breaking through breeding bottlenecks, cultivating new varieties with independent intellectual property rights, and enhancing the core competitiveness of the industry.

Body weight is a paramount breeding target in genetic improvement programs. While traditional selection based on correlations between body weight and external morphological traits had been widely applied in aquaculture [6,7,8,9], this approach overlooked the critical role of internal physiological systems. visceral organs, such as the liver and intestine, were fundamental to metabolic efficiency, nutrient absorption, and energy allocation—processes that directly governed growth performance [10]. Consequently, understanding the relationship between body weight and visceral organ development was essential for a more comprehensive breeding strategy. To date, trait selection based on relationships between morphological characteristics and body weight has been widely employed in genetic breeding across animal and plant species, particularly in aquaculture. Numerous studies have investigated the correlation between body weight and external morphological traits in species such as Pampus argenteus [11], Siniperca chuatsi [12], Lates calcarifer [7], and Seudosciaena polyactis [13]. Most of the research is about the correlation between fish weight and other morphological traits. However, there is a lack of research on the correlation between body weight and the development of internal organs (such as liver, intestine, swim bladder, gonads, etc.). Furthermore, organ weight, as an important basis for evaluating the nature and degree of internal organ lesions, is a routine testing item in drug toxicology research and provides reference for drug safety evaluation [14]. At present, there are few reports on aquatic animals such as Larimichthys crocea [15] and Epinephelus marginatus [16]. This knowledge gap was particularly acute for P. ussuriensis, a species exhibiting remarkable sexual dimorphism in, where males significantly outperformed females [4,5]. This pronounced growth disparity suggested that males and females employed divergent physiological strategies for energy utilization and partitioning, which could be reflected in the differential development of their visceral organs. Although understanding the direction and strength of trait correlations is valuable, it alone cannot fully elucidate the direct and indirect effects among dependent variables. Path analysis allows the decomposition of correlations into direct and indirect effects, thereby enabling the evaluation of causal relationships and providing a comprehensive interpretation of trait associations. Currently, most research on P. ussuriensis has focused on fundamental biology and reproductive technologies, leaving a gap in the systematic analysis of the relationship between growth traits (particularly body weight) and internal organ development. Therefore, path analysis was applied for the first time to this species in this study. Through quantification of the influence pathways of six major visceral organs, the dominant role of the swim bladder in males and the intestines in females was revealed, and a critical knowledge gap in this field was thereby filled. This research not only elucidated gender-specific growth strategies from the perspective of physiological mechanisms but also provided new insights for the collaborative selection of multiple traits. Broad implications for the precision breeding of economically significant aquatic fish species were held by its methodological approach and findings.

Therefore, this study was designed to address this specific research gap. Our primary research question was to clarify the relationship between body weight and key visceral indicators in P. ussuriensis and to determine how these relationships differed between sexes. Through correlation analysis, path analysis, and regression modeling, we aimed to quantify the direct and indirect effects of major visceral organs on body weight for males and females separately. It is particularly important to clarify these gender specific growth strategies; it has direct significance for improving the diversity and efficiency of aquaculture breeding.

2. Materials and Methods

2.1. Experimental Materials

A total of 139 one-year-old P. ussuriensis specimens were obtained from a breeding base in Luoyang, comprising 66 males, 63 females, and 10 individuals of undetermined sex. The fish were reared in an outdoor cement tank (150 m² surface area, 1.4 m water depth) under continuous micro-flow water exchange conditions, with a daily exchange rate of 100–150%. The water quality parameters were maintained as follows: pH 7.8–8.2, temperature 15–28 °C, dissolved oxygen ≥ 7 mg/L, and stocking density 40–50 individuals/m³. Feeding was conducted at a rate of 3–5% of total body weight, in accordance with established breeding protocols developed by our research group [17]. The sexual maturity age of the P. ussuriensis in the natural environment was generally 1.5 years old, and the breeding season was from May to July, belonging to the type of multiple egg laying. They feed on small aquatic invertebrates and fish in natural environments. This experiment is fed with compound feed, which mainly consists of fish meal, soybean meal, corn protein powder, etc., with a crude protein content of ≥35%.

2.2. Sample Data Measurement

Fish were fasted for 24 h prior to sampling. Each individual was dissected under anesthesia, and the following visceral organs were carefully excised: intestine (I), liver (L), swim bladder (SB), kidney (K), spleen (S), and gonad (G). Wet weights of these tissues were measured using an electronic balance with an accuracy of 0.01 g; the spleen and gonads were weighed to a precision of 0.001 g.

2.3. Data Processing and Analysis

The measured data were compiled and preliminarily processed using Microsoft Excel 2016. Statistical analyses were performed with SPSS 22.0. Descriptive statistics including mean, standard deviation (SD), and coefficient of variation (CV) were calculated. Pairwise correlations among visceral indices were evaluated using Pearson correlation analysis [18]. To examine the relationship between visceral indices and body weight (BW), multiple linear regression analysis was conducted using a stepwise method, with BW as the dependent variable and organ weights as independent variables. This approach helped mitigate multicollinearity issues. Furthermore, path analysis was employed to decompose the correlation coefficients between body weight and visceral organ traits into direct and indirect effects, thereby quantifying the causal relationships among variables [19,20]. The direct path coefficient (DPC) represents the standardized partial regression coefficient of an independent variable on the dependent variable, while the indirect path coefficient (IPC) reflects the effect mediated through other variables. The direct path coefficient (DPC) is obtained by fitting a multiple linear regression model that includes all standardized visceral traits, and its estimated value is the standardized partial regression coefficient. Indirect path coefficient (IPC) is calculated by multiplying the direct path coefficients on the paths between variables. The conceptual model for path analysis is expressed as follows:

$$r_{ij}=p_{ij}+{\sum }_{k\ne j}{r}_{ik}·p_{kj}$$

(1)

where r_ij is the correlation coefficient between trait i and body weight, p_ij is the direct path coefficient of trait i on body weight, and ∑r_ik⋅p_kj denotes the sum of indirect effects of trait i via other traits k.

$$d_i=p_i^2$$

(2)

$$d_{ij}=2r_{ij}\times p_i\times p_j$$

(3)

where p_i represents the direct effect of the independent variable i, r_ij is the correlation coefficient between the independent variable i and the independent variable j, and p_j represents the direct effect of the independent variable j.

Then, the coefficient of determination was computed based on correlation and path analysis results to quantify the explanatory power of each variable. Data are presented as mean ± SD. Statistical significance was defined as p ≤ 0.05 and p ≤ 0.01, respectively.

3. Results

3.1. Body Weight and Organ Masses in P. ussuriensis

The body weight and organ masses of 66 male and 63 female P. ussuriensis are presented in

Table 1. Comparison of body weight and organ mass between male and female P. ussuriensis.

Index	Male		Female
	Mean ± SD	CV	Mean ± SD	CV
Body weight	9.58 ± 5.37	0.59	9.54 ± 5.17	0.60
Intestine	0.12 ± 0.07	0.64	0.13 ± 0.07	0.62
Liver	0.16 ± 0.09	0.62	0.17 ± 0.09	0.62
Swim bladder	0.08 ± 0.05	0.62	0.08 ± 0.04	0.65
Kidney	0.14 ± 0.10	0.64	0.14 ± 0.08	0.76
Spleen	0.01 ± 0.01	1.77	0.02 ± 0.03	0.94
Gonad	0.05 ± 0.04	0.94	0.04 ± 0.04	0.69

. The mean body weight of males was 9.58 ± 5.37 g, with a coefficient of variation (CV) of 0.59, while that of females was 9.54 ± 5.17 g, with a CV of 0.60. Since all specimens used in this study were one year old, no pronounced sexual dimorphism in weight was detected, as indicated in Table 1. It is worth noting that, both male and female body weights exhibited high coefficients of variation, suggesting considerable dispersion in individual weights. Additionally, the spleen mass showed exceptionally high variability, with CV values of 1.77 in males and 0.94 in females. It was much higher than all other measurement indicators, suggesting that its weight may not be a stable morphological feature, but a highly dynamic physiological state indicator. In comparison, the CV of organs such as the intestine, liver, and swim bladder was relatively low, indicating that the weight to body weight ratio of these organs may be more stable and less affected by short-term physiological fluctuations.

3.2. Correlation Analysis of Organ Mass with Body Weight Within Each Sex of P. ussuriensis

In males, the masses of the intestine, liver, swim bladder, kidney, spleen, and gonad were positively correlated with body mass (p < 0.05). Among these, the correlations for intestine, liver, swim bladder, kidney, and gonad were significant (p < 0.01). No significant correlation was found between spleen mass and swim bladder mass, kidney mass, or gonad mass; however, spleen mass was positively correlated with body weight, intestine mass, and liver mass (p < 0.05). The highest correlation coefficient was observed between swim bladder mass and body weight (R = 0.937), indicating the strongest association among all organs (

Table 2. Correlations relationship between visceral organ weights and body weight in male and female P. ussuriensis.

Sex	Index	Body Weight	Intestine	Liver	Swim Bladder	Kidney	Spleen	Gonad
Male	Body weight	1
	Intestine	0.926 **	1
	Liver	0.898 **	0.866 **	1
	Swim bladder	0.937 **	0.866 **	0.819 **	1
	Kidney	0.909 **	0.838 **	0.810 **	0.871 **	1
	Spleen	0.292 *	0.280 *	0.241 *	0.228	0.176	1
	Gonad	0.602 **	0.572 **	0.562 **	0.548 **	0.473 **	0.165	1
Female	Body weight	1
	Intestine	0.945 **	1
	Liver	0.880 **	0.867 **	1
	Swim bladder	0.944 **	0.919 **	0.861 **	1
	Kidney	0.882 **	0.844 **	0.853 **	0.822 **	1
	Spleen	0.280 *	0.283 *	0.282 *	0.266 *	0.316 **	1
	Gonad	0.627 **	0.544 **	0.561 **	0.604 **	0.524 **	0.344 **	1

Notes: * indicates a significant correlation at the p < 0.05 level; ** indicate significance at the p < 0.01 level. The same notation is used in the following tables.

). In females, all measured organ masses (namely intestine, liver, swim bladder, kidney, spleen, and gonad) were positively correlated with body weight (p < 0.05), with all except spleen showing significant correlations (p < 0.01). Spleen mass was positively correlated with body weight, intestine, liver, and swim bladder mass (p < 0.05), and significantly correlated with kidney mass (p < 0.01). The remaining organ masses also demonstrated significant correlations with body weight (p < 0.01) (Table 2)

3.3. Analysis of the Relationship Between Visceral Organ Mass and Body Weight in P. ussuriensis

Among male P. ussuriensis, the swim bladder exhibited the greatest direct effect on body mass, with a direct path coefficient of 0.292. Furthermore, swim bladder mass was strongly positively correlated with body mass (R = 0.937), identifying it as one of the most influential metric affecting body weight. Regarding indirect effects, the liver demonstrated the largest total indirect effect on body mass, with a cumulative indirect path coefficient of 0.701. Notably, the kidney exerted its strongest indirect influence on body weight via the swim bladder, with an indirect effect value of 0.254. In terms of statistical significance, the direct path coefficients from the intestines, liver, swim bladder, kidneys, and gonads to body weight all reached significant levels (p < 0.01) in males, while that of the spleen was also significant (p < 0.05). In female P. ussuriensis, the direct path coefficients (DPC) of the intestines, liver, swim bladder, kidneys, and gonads similarly attained significance (p < 0.01), with the spleen also reaching a significant level (p < 0.05). Based on the magnitude of DPC values, the organs were ranked as follows: intestines (0.444) > swim bladder (0.271) > kidney (0.237) > gonads (0.120) > spleen (0.038) > liver (0.001). This indicates that the intestine has the most substantial direct effect on body weight in females. From the perspective of indirect path coefficients (IPC), the swim bladder showed the largest indirect effect on body mass through the intestine, with a value of 0.408. However, the liver contributed the greatest total indirect effect (0.898) on body weight among all visceral organs in females (

Table 3. Direct and indirect path coefficient analysis results of visceral organ mass indices on the body weight of male and female P. ussuriensis.

Gender	Independent Variable	Correlation Coefficient	DPC	IPC
				Intestine	Liver	Swim Bladder	Kidney	Spleen	Gonad	Total
Male	Intestine	0.926 **	0.274 **		0.172	0.253	0.182	0.014	0.038	0.659
	Liver	0.898 **	0.199 **	0.237		0.239	0.176	0.012	0.037	0.701
	Swim bladder	0.937 **	0.292 **	0.237	0.163		0.189	0.011	0.036	0.637
	Kidney	0.909 **	0.217 **	0.230	0.161	0.254		0.009	0.031	0.685
	Spleen	0.292 *	0.050 *	0.077	0.048	0.067	0.038		0.011	0.240
	Gonad	0.602 **	0.066 **	0.157	0.112	0.160	0.103	0.008		0.539
Female	Intestine	0.945 **	0.444 **		0.001	0.249	0.200	0.011	0.065	0.526
	Liver	0.880 **	0.001 **	0.385		0.233	0.202	0.011	0.067	0.898
	Swim bladder	0.944 **	0.271 **	0.408	0.001		0.194	0.010	0.072	0.686
	Kidney	0.882 **	0.237 **	0.375	0.001	0.222		0.012	0.063	0.673
	Spleen	0.280 *	0.038 *	0.126	0.000	0.072	0.075		0.041	0.314
	Gonad	0.627 **	0.120 **	0.242	0.001	0.164	0.124	0.013		0.543

* indicates p ≤ 0.05, and ** indicates p < 0.01.

).

3.4. Multiple Linear Regression Analysis of Organ Mass and Body Weight in P. ussuriensis

A stepwise multiple linear regression analysis was performed to model the relationship between organ mass (independent variables, X) and body weight (dependent variable, Y) for both male and female P. ussuriensis. The optimal regression equations obtained are as follows:

For males (R² = 0.943):

Y₁ = 19.857X₁₁ + 11.035X₁₂ + 35.64X₁₃ + 11.993X₁₄ + 21.337X₁₅ + 8.942X₁₆ + 0.217

For females (R² = 0.939):

Y₂ = 30.154X₂₁ − 0.05X₂₂ + 32.072X₂₃ + 14.876X₂₄ − 6.14X₂₅ + 16.371X₂₆ + 0.623

In these equations, Y₁ and Y₂ represent body weight (g) of male and female individuals, respectively. The independent variables X₁₁–X₁₆ and X₂₁–X₂₆ correspond to masses (g) of the intestine, liver, swim bladder, kidney, spleen, and gonads for males and females, respectively. The high R² values (0.943 for males and 0.939 for females), both exceeding 0.85, indicate that the regression models explain over 85% of the variability in body weight, demonstrating strong predictive accuracy and goodness of fit. Detailed parameter estimates for both models are provided in

Table 4. Multiple linear regression parameters for predicting body weight from organ mass in male and female P. ussuriensis.

Sex	Variable	Parameter Estimates	SD	t	Sig.
Male	Constant number	0.217	0.337	1.851	0.000
	Intestine	19.857	5.851	5.154	0.000
	Liver	11.035	3.728	−0.013	0.000
	Swim bladder	35.64	10.647	3.012	0.000
	Kidney	11.993	4.003	3.717	0.000
	Spleen	21.337	5.521	−1.112	0.012
	Gonad	8.942	5.693	2.876	0.000
Female	Constant number	0.623	0.337	1.851	0.000
	Intestine	30.154	5.851	5.154	0.000
	Liver	−0.050	3.728	−0.013	0.000
	Swim bladder	32.072	10.647	3.012	0.000
	Kidney	14.876	4.003	3.717	0.000
	Spleen	−6.140	5.521	−1.112	0.020
	Gonad	16.371	5.693	2.876	0.000

and

Table 5. Coefficient of determination (R²) of the multiple regression model for predicting body weight in male and female P. ussuriensis.

Model	R	R2	Adjusted R2	S. E.	Change Statistics
					R2 Chang	F Chang	Sig.
Male	0.974a	0.948	0.943	1.19666	0.948	179.888	0.000
Female	0.972a	0.945	0.939	1.24959	0.945	156.646	0.000

. The significance test was conducted on the multiple regression equations constructed for these two groups using the F-test method. The results showed that the regression equations for both groups reached a significant level (p < 0.01), indicating that the constructed regression equations had statistical significance (

Table 6. Variance analysis of multiple regression equations for male and female P. ussuriensis.

Sex	Model	Total Sum of Squares	df	Mean Square	F	Sig.
Male	Regression	91,798.079	6	15,299.680	398.767	0.000
	Residual	18,186.170	60	76.735
	Total	109,984.249	66
Female	Regression	34,650.436	6	5775.073	432.395	0.000
	Residual	4354.603	57	13.356
	Total	39,005.039	63

).

4. Discussion

As a core phenotypic trait for assessing growth performance, fish body weight holds crucial significance in commercial aquaculture and genetic breeding programs [21]. It is not only directly tied to the economic output of the processing industry but also serves as a key composite indicator reflecting individual growth rate, feed conversion efficiency, disease resistance, and reproductive potential. This study represents the first systematic investigation into the quantitative genetic relationships between the mass of major internal organs and body weight in one-year-old P. ussuriensis.

4.1. Correlation and Path Analysis

This research systematically quantified the contribution pathways through which major internal organs influence body weight in one-year-old P. ussuriensis. The results demonstrated that the direct path coefficients of the intestine, liver, swim bladder, kidney, and gonads all reached significant levels, with the spleen also showing a significant effect. This indicates that the development of these organs may be among the primary drivers of weight gain. Notably, the swim bladder exhibited the strongest direct effect in males, along with the highest simple correlation coefficient with body weight, underscoring its vital role in energy metabolism and buoyancy regulation in male growth strategies [22]. In females, the intestine had the most substantial direct impact on body weight, significantly exceeding that observed in males. This suggests that females may prioritize enhancing the developmental efficiency of nutrient-absorbing organs such as the intestines to meet the high energy demands associated with future ovarian development. The intestine and liver, as central digestive organs, play essential roles in nutrient absorption and metabolic regulation [23]. An organism’s feeding and digestive capabilities directly influence its growth trajectory; a more developed digestive system typically corresponds with stronger feeding capacity and more rapid growth [24]. In this study, all organs except the spleen showed significant correlations with gonadal mass, indicating that sexual dimorphism influences organ development. The generally higher body weight observed in males may be attributed to sex-based differences in foraging behavior and feed intake rates, ultimately leading to divergent growth patterns between sexes—a finding consistent with previous reports [15]. Path analysis further elucidated not only the direct contributions of organs but also the network of indirect effects mediated through interorgan interactions [25]. In males, the kidney exerted the largest indirect effect on body weight via the swim bladder, implying a functional synergy between the kidney and swim bladder in maintaining osmotic balance and energy allocation conducive to growth. In females, the most notable indirect effect was that of the swim bladder acting through the intestine, highlighting a robust functional coupling between these organs—where swim bladder condition (implicated in gas exchange and possibly metabolic regulation) significantly influences intestinal function and thereby weight gain. Although the spleen’s direct effect on body weight was modest (0.050 in males, 0.038 in females), it showed significant positive correlations with body weight and multiple visceral indices (e.g., intestine and liver), particularly reaching a significant correlation with the kidney in females (p < 0.01). This suggests the potential existence of an “immune–growth axis.” Moreover, the high coefficient of variation in spleen mass may reflect substantial interindividual differences in immune status or stress response, a phenomenon also documented in other teleost species such as yellow catfish [26], rainbow trout [27], and eel [28]. These variations likely indirectly modulate growth performance through interactions with other organs—a compelling direction for future research incorporating immunohistological approaches.

4.2. Analysis of Multiple Linear Regression

The development of sex-specific multiple linear regression models (males: R² = 0.943; females: R² = 0.939) signifies a shift from traditional phenotype-based selection toward breeding strategies targeting key internal organs. By weighting organ-level contributions to body weight (BW) via standardized path coefficients and regression weights, these models unveil the physiological underpinnings of sexual dimorphism (Du and Chen, 2010, [25]). In males, the swim bladder possessed the highest direct path coefficient (0.292) and regression weight (35.64), significantly surpassing those of other organs (p < 0.05), indicating a tight coupling between swim bladder mass gain and overall weight increase. This may be attributed to the swim bladder’s dual functions in buoyancy control and optimization of energy metabolism. corroborating Evans and Page (2003) [22], who reported a positive correlation between swim bladder length and body size across 18 perciform species. In females, intestinal dominance was evident, reflected in the highest regression coefficient for intestinal weight (30.154–51.8% higher than in males) and the strongest direct effect (path coefficient = 0.444). This aligns with energy allocation theory, wherein nutrient absorption efficiency is prioritized in support of ovarian development and reproductive investment. Notably, negative coefficients emerged in the female model—liver weight (−0.050) and spleen weight (−6.140) correlated negatively with body weight—although no significant direct negative effects were detected in path analysis. This may indicate that these organs divert energy away from growth processes. The negative coefficient for liver weight might reflect an energy allocation trade-off in sexually maturing females. The liver is the primary site for vitellogenin synthesis, a highly energy-demanding process crucial for ovarian development. Thus, energy investment in reproductive preparation via hepatic function might divert resources away from somatic growth, leading to a negative association in the model when other organs are accounted for. Similarly, the substantial negative coefficient for spleen weight could signify an ‘immuno-growth’ trade-off. An enlarged spleen is often associated with enhanced immune activity or response to pathogens. Sustained immune activation is energetically costly, potentially limiting the energy available for growth. Hence, a heavier spleen might indirectly indicate an individual under physiological stress, which compromises weight gain.

Overall, the regression models facilitate early growth prediction by integrating six visceral indicators across sexes of P. ussuriensis. The resulting equations, which incorporate intestine, liver, swim bladder, kidney, spleen, and gonads as independent variables, exhibit high explanatory power (R² > 0.90), providing a predictive tool for estimating body weight variation resulting from combined visceral contributions. The limitation of this study lies in the fact that only one-year-old Pseudobagrus ussuriensis were used, which somewhat restricts the generalizability of the findings across different growth stages. The relationship between visceral organs and body weight may indeed change with sexual maturation and aging, particularly in organs closely associated with metabolism and reproduction, such as the gonads and liver. However, as research on P. ussuriensis continues to expand, fundamental datasets will be further refined. Additionally, in this study, all organ weights were measured and analyzed using the original wet weight. Although this approach effectively reflects the absolute developmental level of the organs, it was not standardized for body weight, which may introduce slight bias when significant individual size differences exist. It is recommended that future studies incorporate relative organ indices (such as organ weight/body weight) or histological indicators (such as tissue structural integrity, cell count, etc.) to more accurately assess organ functional status and its relationship with growth performance. Collectively, this study established an “organ-targeted” breeding framework that integrates physiological mechanisms with genetic improvement strategies.

5. Conclusions

In this study, we employed path analysis to investigate the causal network linking visceral organ development and body weight in one-year-old P. ussuriensis. For the first time, the direct and dominant contributions of the swim bladder in males and the intestine in females—as core organs—to growth performance were quantitatively assessed. Based on these findings, a high-precision sex-specific regression model was developed to accurately predict growth traits from organ metrics. This research addresses a significant gap in understanding the systematic relationship between visceral development and overall growth in P. ussuriensis. The results provide foundational insights into the physiological correlations between key organs and body weight, thereby supporting future efforts in genetic breeding and variety improvement of this species.