Length-weight relationship and condition factor
In the present study, the b value of
L. microdon was estimated 2.57 (male), 2.51 (female)and 2.54 (pooled) whereas coefficient of determination (r
2) was 0.94 (male), 0.94 (female) and 0.90 (pooled) respectively (Table 1 and Fig 2).
In the length-weight relationship of fishes, the b values were typically found between the estimated ranges of 2.5-3.5 (
Froese, 2006).
Ontomwa et al., (2018) and
Matthews et al., (2019) have estimated growth co-efficient (b) estimates for
L. microdon (2.6)
, which are in the same line of the present findings.
Mehanna et al., (2017) and
Al Kamel et al. (2020) observed b values as 2.9 and 3.1 for
L. microdon which is higher than the recent findings, confirming the presence of a negative allometric pattern in this species, which is in line with the present study.
Rajathy et al., (2021) estimated the slope value for
L. lentjan (2.9) and
L. microdon (2.8) which is higher than the current investigation.
Grandcourt et al., (2010) and
Daliri et al., (2012) registered a b value of 3 for
L. microdon from the Southern Arabian Gulf and Northern Persian Gulf, which is higher than present observation.
Thangaraj et al. (2022) reported b value for
L. microdon (2.8) which is slightly higher than the present estimation.
Vasantharajan et al., (2014) and
Zaahkouk et al., (2017) estimated an almost identical b value of 3.0 for another species of lethrinid (
L. lentjan) along the Indian coast and Red Sea, which are lower than the current findings.
Currey et al. (2009) and
Vasantharajan et al., (2014) reported a slope value of 2.9 for
L. nebulosus from the Great Barrier Reef and Thoothukudi, Southeast coast, India, confirming the negative allometric as observed in the present study. Additionally,
Daliri et al., (2012) reported a slope value of 2.6 for
L. nebulosus from the Northern Persian Gulf, which is in conformity with the current observation. In comparison with the previous estimates, some variations in the b values were noted in the current study. These differences could be due to several factors, including fish physiology, growth phase, sex, sexual maturity, season, stomach fullness, length range and sample size, habitat, feeding rate, dietand health (
Le Cren, 1951;
Froese, 2006;
Mondol et al., 2017). Additionally, sampling bias might also occur due to the use of different gears, or absence of an independent and uniform sampling technique or relatively small sample size or narrow size range which may also affect the accuracy of b values as mentioned by
Roul et al., (2017c).
The fulton condition factor (
KF) of
Lethrinus microdon were estimated 1.22 for male, 1.33 for female and 1.19, for pooled, which reveals that these species are in good condition in the waters of the Gulf of Mannar (Table 1).
Rajathy et al., (2021) recorded a
KF value of
L. nebulosus as 1.44 from the Thoothukudi coast, India, which is in conformity with the present study.
Ravikumar et al., (2023) reported the Fulton condition factor values from 1.3357 to 2.5846 for demersal reef fishes from the Gulf of Mannar, India, which is higher than the present findings. The results indicate that the ecological conditions in the waters of the Gulf of Mannar, located off the southeast coast of India, are favourable for the growth of
Lethrinus microdon species. Additionally, the condition factor values nearing to one and more than 1 could be attributed to the well-being of the fish in the ecosystem besides the optimal environmental factors which are very conducive for the better growth and reproduction of the species. The health of fish varies slightly from habitat to habitat, possibly due to factors such as population size, food intake, reproductive development, sex, time of year and geographic location. When the condition factor e” 1, it indicates healthy growth condition of fish, whereas <1 signifies poor growth condition
(Jisr et al., 2018). It can be influenced by both living and non-living factors, such as water quality and the food availability and predators
(Blackwell et al., 2000).
Food and feeding habits
The analysis of gut contents indicated that fish constitutes the majority of the diet (50-60%), followed by crustaceans (40-50%) and mollusca (20-30%) and echinoderms (10%). The primary and most significant prey items were teleosts, crustaceans (including brachyurans and carideans)and molluscs (both gastropods and bivalves). In addition to the prey items, coral rubble and sand particles were also found in the gut. After analysed the gut samples,
L. microdon can be regarded as a piscivorous species. These fish have a low-bodied form with conical teeth, enabling them to feed on fast-moving prey like nekton (
Carpenter, 1996). The present observations also found similar results like studies by
Randall (1995) and
Carpenter and Allen (1989) which indicate that their primary prey consists of fish, followed by crustaceans, mollusksand polychaetes. This result is confirmed by
Ali et al., (2016), but does not correspond to
Fischer and Bianchi (1984) who stated that
L. microdon feeds on crustaceans, mollusks and small fish.
L. microdon typically feed primarily on fish, crustaceans, molluscan, with a smaller portion of their diet consisting of benthic prey. Clupeidae was the main prey, making up the largest percentage of
L. microdon diets. Smaller specimens were found to consume an abundance of benthic invertebrates, while larger individuals showed a dietary shift. This change is attributed to their solitary behavior, wider home rangeand body morphology, which allows for faster swimming and the ability to target more mobile prey compared to subadults or juveniles. In younger specimens, mollusks, particularly bivalves, were found in notable amounts, whereas in adult fish, nekton became the primary dietary component due to their higher nutritional needs. The results also indicate ontogenetic changes in diet composition, which vary based on growth patterns, seasonal factorsand prey availability. The Gastrosomatic index (GaSI) value of
L. microdon were ranged from 1.45-2.37 for male and 1.89-4.34 for female, respectively (Table 2 and Fig 3).
The Hepatosomatic index (HSI) value were ranged from 0.45-2.54 for male and 1.11-3.21 for female, respectively (Table 2).
Reproductive characteristics
Sex ratio
The overall sex ratio of male and female was observed to be 1:0.67 (Table 3).
The observed sex ratio was tested against 1:1 using the chi-square test for (n-1) degrees of freedom at 5% level of significance. The chi-square test indicated that there was no significance difference (p>0.05) in the average sex ratio and month-wise sex ratio (Fig 4).
Grandcourt et al., (2010) observed the overall male: female ratio of
L. microdon was 1:1.6, which is higher than present findings. In his study, male was more dominant than female in the present study. According to
Al-Areeki et al., (2007) reported a overall sex ratio for
L. lentjan were estimates to be 1:1.1 (Male:Female) in the Red Sea coast of Yemen which is higher than the present findings. Other similar study were reported by
Damora (2018) 1:1.08 for
L. lenjan in Indonesia waters;
Degoon and Ali (2016) estimated the overall sex ratio was 1:1.7 for
L. mahsena in the Sudanese Red Sea,.
Kulmiye et al., (2002) estimated sex ratio was of
L. lentjan were estimated to be 1.0:1.10 in Kenyan coastal waters, present findings. In the study males were more dominant than female. The sex ratio may fluctuate from the predicted 1:1 ratio from species to species, or even within the same population adaptability, reproductive behavior, food availability and environmental conditions
(Asut et al., 2019).
The gonadosomatic index (GSI) value of
Lethrinus microdon was ranged from 1.21-2.21 for male and 1.85-2.31 for female (Fig 5).
Al-Areeki et al., (2007) reported a maximum GSI value of 2.43 (March) for another
Lethrinus species, (
L. lentjan) which is lower than the present study. Similar results recorded by
Currey et al., (2009) and
Ebisawa (1990) revealed high GSI value in July-August in Australia and Okinawan waters. The highest GSI value was recorded in
L. mahsena (3.23) in June 2023 and the lowest value (0.26) was recorded in September 2023. Similar results were recorded by
Soondron et al., (1999) in Mauritius water. Interestingly, their stomachs are fullest between September to November, but less full during the spawning season from June to August.
Length at first maturity
The length at which 50% of all fish of a particular size reach maturity is referred to as the length at first maturity (L
50). For both male and female
L. microdon, the L
50 attains maturity was 25.5 cm for male and 26.5 cm for female (Fig 6 and 7).
Toor (1964) documented an L
50 of
L. lentjan was found 30 cm for male and 28.7 cm for female in the Indian Ocean, whereas
Grandcourt et al., (2010) observed an L
50 of
L. microdon was estimated 24.6 cm for male and 27.7 cm in the Arabian Gulf, which is similar with the present findings. The present study differs from another species of
Lethrinus (
L. lentjan), attained length at first maturity of female at 26 cm in Red Sea Coast of Yemen by
Al-Areeki et al., (2007), which is similar than the present investigation.
Mrombo et al., (2019) observed that the L
50 for male and female
L. lentjan was 25.8 cm. and 26.2 cm, which are in agreement with the present findings.
Toor (1964) reported an L
50 of 30 cm for males and 28.7 cm for females (
L. lentjan) in Indian Ocean waters, while
Grandcourt et al., (2010) reported an L
50 of 24.6 cm for males and 27.7 cm fork for females (
L. lentjan) in the southern Arabian Gulf.
Damora et al., (2018) reported L
50 of
L. lentjan as 25.1 cm for males and 25.3 cm for females, which is similar with the present findings. The gaps in first sexual maturity values could be changed due to variations in diet, water temperature and stock population (
Reznick, 1993). These differences may be also linked to varying levels of fishing pressure in different regions, as
Lappalainen et al., (2016) suggested, noting that L
50 can be a potential indicator of fishing pressure in fish stocks.
Maturity stages
The occurrence of various maturity of the gonad in different months showed that the peak spawning of
L. microdon was in June to August. The simultaneous occurrence of immature, maturing, mature and ripe individuals in a number of months and evidence obtained from the hepatosomatic index and gonadosomatic index support above inferences. The observations of gonad maturity stages across different months revealed that peak spawning of
L. microdon typically occurs in June to August in whole year.
Motlagh et al., (2010) reported peak spawning of
L. nebulosus in March in the Persian Gulf and Oman Sea.
Al-Areeki et al., (2007) reported peak spawning of
L. lentjan in April-May in the Yemen coastal water.
Mrombo et al., (2019) reported peak spawning of
L. lentjan in January in Kenya waters, there was no reported study on the maturity stages in
L. microdon, although in the same genus of different species were reported.
Toor (1964) also observed the peak spawning of
Lethrinus species occurring June – August in Indian waters. The present study also indicated same peak spawning season. Spawning season can vary from region to region due to the environmental factors.
Fecundity
The total fecundity was ranged from 70,345 to 5,09,735 eggs.
Al-Areek et al. (2007) reported 80295 to 837251 eggs of another
Lethrinus species (
L. lentjan) in Yemen coastal water, which is higher than the present findings.
Mrombo et al., (2019) reported 90 to 3,80,364 eggs of
L. lentjan in Kenya waters, which is higher than the present investigations.
Toor (1964) reported 12,146-77,922 eggs of
L. lentjan in Indian water, which is lower than the current findings.
Degoon and Ali (2016) estimated absolute fecundity of
L. mahsena was 2,26,667-1,646,667 eggs per mature female, which is higher than the present investigation. According to
Toor (1964) the fecundity of
L. mahsena was 26,700-166200 eggs (
Carpenter and Allen, 1989) which is lower than the present findings. The fluctuation may arise from various environmental factors like temperature, sunlightand weather conditions (
Jonsson and Jonsson, 1999).
