Reproduction of an isolated Iranian cichlid, Iranocichla hormuzensis

Reproduction of an isolated Iranian cichlid, Iranocichla hormuzensis

Y, Keivany* and E, Daneshvar

Dept. of Natural Resources (Fisheries Division), Isfahan University of Technology, Isfahan 84156-83111, Iran

* Corresponding author’s E-mail: keivany@cc.iut.ac.ir

(Received: Aug. 26.2014 Accepted: Feb. 17.2015)

INTRODUCTION

Cichlids are comprised of about 150 genera and 1300 species, making it the second largest perciform family (Nelson, 2006). Cichlid fishes have a worldwide distribution and they are found in fresh and brackish waters of Central and South America, Africa, Madagascar, the Levant, southern India, Sri Lanka and southern Iran.  Due to cichlid’s economic importance, they are becoming increasingly prominent in freshwater aquaculture at many regions of the world. Cichlids have a dazzling array of body shape and color, which makes them one of the most important groups of aquarium fishes (Berra, 2001). Cichlids exhibit a broad range of morphological, ecological and behavioral variations. The Iranian cichlid, Iranocichla hormuzensis Coad, 1982, is the only endemic species of cichlids in Iran (Coad, 1982; Berra, 2001). This species is found in the Hormuz basin (southern Iran) in rivers with warm and salty water (Esmaeili et al., 2008). They are recognized by the darkened rays and lack of spots in the pectoral fin and specially, by the single nostril opening on each side of the head (Coad, 1982). Trewavas (1983) placed Iranocichla in the genus Danakilia but also agreed with (Coad, 1982) who believed that Iranocichla and Danakilia might be related to the genus Tristramella. Esmaeili et al., (2008) investigated some aspects of reproductive biology of I. hormuzensis in the upstream of Mehran River. In this study we present information on sex ratios, reproduction, gonadosomatic index (GSI), hepato-somatic index (HIS), fecundity and condition factor of I. hormuzensis from lower Mehran River which is ecologically different from the upstream (e.g. higher salinity, higher temperature, etc.).

Fig. 1. Map of Iran, showing the collection site in Mehran River.

Materials and methods

The specimens were sampled from the Dezhgan in Mehran River at 26°52´53˝N, 55°16´21˝E (Hormuzgan Province) (Fig. 1). The bottom structure of sampling area was sandy-muddy. During August 2008 and August 2009, a total of 486 individuals were captured using seine net (8 m × 1 m, 5 mm mesh size), by searching the substrate for 120 to 150 minutes. During each collection, the temperature of the water surface was recorded once a month. Then, specimens were fixed into 10% formalin and transferred to the laboratory for further examination. Information recorded for each specimen were total length (TL) and standard length (SL), to nearest 1 mm and body mass (M) to the nearest 0.01 g. Condition factor was calculated according to the formula: K = (W/ L3) × 100, Where W = body mass in g and L = total length (TL) in mm (Bagenal, 1978, Ricker, 1975). The gonads and liver were removed and weighed with a digital scale to the nearest 0.001g. To determine the reproductive cycle and the breeding season, we measured five indices including gonadosomatic index (GSI = 100×Gonad Mass/Body Mass) (Nikolsky 1963), hepatosomatic index (HIS = 100 × Liver Mass/Body Mass), modified gonadosomatic index (MGSI =100×Gonad Mass /Fish Mass− Gonad Mass) (Nikolsky, 1963), Dobriyal index (DI = ) (Dobriyal et al. 1999) and reproductive condition. The ratio of gonad mass to the length, RC = GW/TL where GW is gonad mass in g and TL is total length in mm (Way et al., 1998) was calculated. The absolute fecundity, as the number of mature ova likely to be spawned, was calculated using ripe ovaries with higher gonadosomatic index (Batts, 1972). Fecundity was estimated from 15 fish in the ripe macroscopic stage. The ovaries were placed in Gilson’s solution. The maximum length and width of oocytes in ovaries preserved in 4% formalin solution was measured using an ocular micrometer. Fertility co-efficient (FC) was estimated according to Riedel (1969): FC = E/TL3, Where E = number of eggs produced and TL = total length of female fish (mm). The regressions between fecundity (F) and total length (TL), body mass (M), condition factor (K) and ovary mass (GW) were calculated. All statistical analyses were carried out using SPSS ver. 15.

RESULTS

Monthly water temperature during this study varied from 16ºC to 34ºC, decreasing from August to February and then increasing from February to August (Fig. 2). Water temperature in reproductive season (March to May) was 23ºC to 30ºC with an average of 27ºC. The salinity of water decreased from 37‰ in August to 34‰ in May. In March, the number of I. hormuzensis increased in deeper waters, and at that time, nests observed in shoreline with calm and clear water (Fig. 3a). The number of nests rapidly increased in April and May and decreased afterwards (Fig. 3b). These nests were usually observed on muddy-sandy bottoms in multiple groups (3-4). The length and width of these nests were about 20×25 cm.

A total of 486 specimens of I. hormuzensis with distinct gonads were examined. Therewere 252 (51.85%) males and 234 (48.15%) females. The sex ratio of the collected samples was 1Male:0.93Female. Overall Chi-square test (χ²) showed an insignificant difference between the two sexes (χ², df = 1, P = 0.414), but in some months, sex ratio changed significantly (Table 1). There was a significant difference in the male/females ratio in the five size classes of I. hormuzensis (Table 2). The ovarian mass ranged between 0.0035 g and 0.4782 g. (Mean ± SD: 0.0350 ± 0.0568 g). Monthly variations in GSIrevealed that both sexes follow nearly the same pattern. The gonadosomatic index (GSI) varied significantly in different months (ANOVA, df = 12 P = 0.0001) (Fig. 4). The GSI showed higher values for females (7.12 ± 1.0206) than males (0.8149 ± 0.1047) from February to June with a peak in March, while the lower ones occurred from July to January. There was an increase in spawning intensity in early March to end of May and lasted until the early June. The total number of ripe eggs in the ovary (absolute fecundity) ranged between 48-167 eggs with a Mean ± SD of 107 ± 35.2 for fish with total length range (TL) of 58-76 mm and a Mean ± SD egg diameter of 1.92 ± 0.73 mm (0.58–2.93 mm). Fecunidity was better correlated with total body mass (M), condition factor (K) and total length (TL) (Table 3). The Mean ± SD fertility co-efficient for this fish was 0.0003949 ± 0.00009246. Fertility co-efficient did not correlate with body mass and length, it showed the highest correlation with gonad mass (linear regression, r² = 0.4105).

The hepatosomatic index (HSI) is an indicator of annual morphological changes in the liver and associated with gonad development. The hepatosomatic index (HSI) showed a sharp decreaseforboth sexes, when GSI was elevated (from February to March) (Fig. 5). In April, HSI increased for males, but decreased for females. The hepatosomatic index (HSI) showed a general increase for males and females immediately following the end of the reproductive season. These data indicate that excess energy gained by I. hormuzensis is used for reproduction during February to May, and is stored as glycogen in the liver after the reproduction season.The monthly Mean ± SD condition factor for females and males ranged from 0.0696 to 0.5127 (0.1747 ± 0.0665) and 0.0412 to 0.4671 (0.1882 ± 0.0689), respectively. Condition factor values for females were the highest in April and October and the lowest in February and December. On the other hand, for males, the highest values were in November and December and the lowest in September and August.

Fig. 2. Monthly water temperature in lower Mehran River during August 2008-August 2009.

Fig. 3. Nest of I. hormuzensis in March (a) and April (b) in lower Mehran River.

Table 1. Monthly proportion of male and female I. hormuzensis in lower Mehran River.

Table 2. Percentage of male and female I. hormuzensis in different size groups in lower Mehran River.

Table 3. Relationship between Fecundity and body mass, condition factor and total length in I. hormuzensis.

Fig. 4. Monthly variations in the gonado-somatic index of I. hormuzensis.

Fig. 5. Monthly variations in the hepato-somatic index of I. hormuzensis.