Comparison of urohyal bone morphology among gerreid fish (Perciformes: Gerreidae)

Figures & data

Figure 1. (A). Left side view of an urohyal bone in Gerreidae fish. Terminology of urohyal as follows: Ha = hypohyal attachment; Ba = basibranchial attachment; Ve = ventral extension; De = dorsal extension; Dp = dorsal plate; Pde = postero-dorsal edge; Rb = radial band; Lp = lateral plate; Pe = posterior edge; Ve = ventral edge; Vp = ventral plate; Co = condyle (modified from Kusaka 1974). Circle and cross indicating the orientation of urohyal on the body plan: D = dorsal; V = ventral; A = anterior; P = posterior. (B). Urohyal bone position during closure (I) and opening (II) of the oral cavity, exemplified in Eugerres lineatus (Cuvier, 1830), the striped mojarra. Note that only for illustration purposes the bone is depicted over the opercle, disconnected from basibranchial (anterdorsal) and hypohyals (ventral).

Table I. Number of samples (n), standard length range (SL, mm) and mean (m SL) of Gerreidae fish collected and used in the urohyal morphology analysis.

Species	n	SL	m SL
Diapterus auratus	32	75.0–144.0	113.75
Diapterus brevirostris	58	46.0–170.0	115.73
Eugerres lineatus	22	108.0–210.0	160.43
Eugerres plumieri	24	81.0–205.0	149.95
Eucinostomus entomelas	47	58.0–74.0	62.17
Gerres cinereus	39	100.0–225.0	178.66
Totals	222

Table II. Kolmogorov-Smirnov (K-S) test of normality at the 95% confidence level for the urohyal raw untransformed data (RUD), and standardized measurements (SM). Perimeter was transformed by the Box-Cox function. *Not normally distributed.

Measurements	RUD		SM
	K-S	p	K-S	p
Area	0.092	0.0460*	0.038	0.9060
Aspect ratio	0.194	0.0001*	0.145	0.0001*
Diameter max.	0.082	0.1040	0.062	0.3660
Diameter min.	0.117	0.0040*	0.115	0.0060*
Diameter mean	0.151	0.0001*	0.053	0.5570
Perimeter	0.102	0.0200*	0.074	0.1800
Roundness	0.090	0.0560	0.090	0.0560
Feret minimum	0.127	0.0020*	0.069	0.2430
Feret mean	0.103	0.0170*	0.061	0.3770
Form-factor	0.239	0.0001*	0.048	0.6880
Circularity	0.103	0.0180*	0.087	0.0690
Rectangularity	0.041	0.8430	0.045	0.7700
Ellipticity	0.093	0.0420*	0.066	0.2950

Figure 2. Morphology of the urohyal bone in Gerreidae species. (Da) Diapterus auratus, (Db) D. brevirostris, (El) Eugerres lineatus, (Ep) E. plumieri, (Ee) Eucinostomus entomelas and (Gc) Gerres cinereus. Scale bars: for urohyals, 0.5 mm, and 1 cm for fish.

Figure 3. Box plots comparing Feret maximum (Fmx, i.e. the size estimator) for the urohyal bone of six Gerreidae species (raw untransformed data): (Da) Diapterus auratus, (Db) D. brevirostris, (El) Eugerres lineatus, (Ep) E. plumieri, (Ee) Eucinostomus entomelas and (Gc) Gerres cinereus, showing the mean (+), median (dashed lines), quartiles, standard deviations (SDs; grey boxes) and range values (minimum and maximum). Sample sizes are given in Table I (● and * indicate, respectively, individual values greater than 1.5 and 3 times the interquartile range from the nearest quartile).

Table III. Classification matrix as a result of discriminant function analysis testing for differences between analyzed Gerreidae species based on 13 urohyal shape and size descriptors. (Da) Diapterus auratus, (Db) D. brevirostris, (El) Eugerres lineatus, (Ep) E. plumieri, (Ee) Eucinostomus entomelas and (Gc) Gerres cinereus.

Actual group			Predicted	group	membership		Urohyals by species	c.c. %
	Da	Db	El	Ep	Ee	Gc
Da	28	4	0	0	0	0	(32)	87.50
Db	1	56	0	1	0	0	(58)	96.55
El	0	0	19	2	0	1	(22)	86.36
Ep	0	0	2	22	0	0	(24)	91.67
Ee	0	0	0	0	43	4	(47)	91.49
Gc	0	0	0	3	0	36	(39)	92.31
Totals	29	60	21	28	43	41	(222)	91.89

Underlined: quantity of correctly classified urohyals for each species; sample sizes in parentheses. c.c. % = correct classification percentage by species. Overall mean classification success = 91.89%. Cohen’s kappa = 0.90, p < 0.001; G-test = 638.95, p < 0.000.

Figure 4. Scatter plots of first (F1) and second (F2) discriminant functions. Discriminant function analysis (DFA) using 13 urohyal shape and size descriptors of the six species of Gerreidae. The first discriminant axis (F1) explains 71.73% and the second axis (F2) 15.02%. (Da) Diapterus auratus, (Db) D. brevirostris, (El) Eugerres lineatus, (Ep) E. plumieri, (Ee) Eucinostomus entomelas and (Gc) Gerres cinereus.

Table IV. Mahalanobis distances between groups (above the diagonal) and p value of the F test (below the diagonal). Da: Diapterus auratus, Db: D. brevirostris, Ee: Eucinostomus entomelas, El: Eugerres lineatus, Ep: E. plumieri and Gc: Gerres cinereus.

	Da	Db	Ee	El	Ep	Gc
Da	----	3.39324	7.34064	6.43998	8.60100	7.73250
Db	< 0.0001	----	7.61322	7.14226	9.04735	8.17847
Ee	< 0.0001	< 0.0001	----	5.24723	4.81404	3.16790
El	< 0.0001	< 0.0001	< 0.0001	----	3.68138	5.04403
Ep	< 0.0001	< 0.0001	< 0.0001	< 0.0001	----	5.13344
Gc	< 0.0001	< 0.0001	< 0.0001	< 0.0001	< 0.0001	----

Figure 5. Phenogram indicating the phenotypic relationship of the urohyal morphology (shape and size measurements) for Gerreidae species: (Da) Diapterus auratus, (Db) D. brevirostris, (El) Eugerres lineatus, (Ep) E. plumieri, (Ee) Eucinostomus entomelas and (Gc) Gerres cinereus. Dissimilarity based on the Euclidian distance of Mahalanobis distance values, grouping by hierarchical cluster analysis (UPGMA).

Kusaka T. 1974. The urohyal of fishes. Tokyo: University of Tokyo Press.

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