Effects of body weight ranges on variations in morphological traits of parent snails and eggs obtained from their matings in Obubra, Nigeria

Effects of body weight ranges on variations in morphological traits of parent snails and eggs obtained from their matings in Obubra, Nigeria

Effects of body weight ranges on variations in morphological traits of parent snails and eggs obtained from their matings in Obubra, Nigeria

*1Ibom, L. A., 2Okon, B. and 3Isaac, L. J.

1Department of Animal Science, Ebonyi State University, Abakaliki, Nigeria.

2Department of Animal Science, University of Calabar, Calabar, Nigeria.

3Department of Animal Science, University of Uyo, Uyo, Nigeria.

Corresponding author's E-mail address: ibomlawrence@gmail.com

ABSTRACT

This study provides information on the morphological characteristics of parent snail ectotypes (black-skinned and white-skinned) and eggs obtained from their mating. Correlation between the parent snail traits and the egg traits were estimated. Forty snails, twenty each of the black-skinned (BS) and white-skinned (WS) ectotypes were used for the study. The snails which were managed in wooden cells were grouped in a mating arrangement of one black-skinned ectotype to one white-skinned ectotype per cell and monitored for three months (May to July). Morphological traits measured on parent snails included initial body weight, shell length, shell width, aperture length and aperture width, while those measured on eggs were clutch size, egg parameters at lay (weight, length and width), incubation period and percent hatchability. The results of this study showed that all traits measured on the parent snails varied within and between the four body weight groups evaluated. The variations within groups (that is between the black-skinned (BS) and the white-skinned (WS) ectotypes) for body weight were not statistically different (P>0.05). The trend in non significant difference was also observed in other traits measured on the parent snails. However, there were significant differences (P0.05) different between ectotypes among the groups. The results of correlated relationships among morphological traits measured on BS and WS parent snails and their eggs showed that all the traits evaluated were either positively correlated or had zero correlation. The results of this study showed that improvement of the morphological traits evaluated on both the parent snails and their eggs is possible through selection. Interested snail farmers are therefore encouraged to establish suitable commercial production stocks by crossbreeding the BS and WS ectotypes of snails.

Key words: Bodyweight, variations, snail eggs, mating, morphological traits,

ectotypes.

INTRODUCTION

Over the years, Nigeria like other developing countries has depended on poultry for the growth of her livestock industry. However, the production and subsequent consumption of poultry products appear threatened. This is because of occasional epidemics associated with poultry across the globe. A good example is the bird flu (Avian influenza) pandemic. Besides, other species and sources of red meat are also threatened by certain ugly incidences. Swine fever (swine flu) being a good example. These will further worsen the unavailable animal protein in developing countries during this period of economic melt-down. In the light of this, there is need to diverge the conventional attitudes to change and embark on intensive research to discover novel meat producing animals to complement the supply from conventional livestock if the 2015 Millennium Development Goal (MGD) agenda for animal protein intake sufficiency must be achieved. Ayeni and Ajayi (1983) recognized wild life domestication as one of the virgin areas capable of solving animal protein intake deficit in Nigeria. Snails, Cane rats, Guinea pigs and giant African rats are among wild life species that are yet to be fully explored and exploited.

Meat (Congo meat) from snails gathered or collected from the wild has traditionally been a major ingredient in the diet of West Africans living in the humid tropical zone (Ejidike 2002 and Ibom 2009). According to Imevbore (1990), Adeyeye (1996), Amusan and Omidiji (1998), Payne and Wilson (1999) and Akinnusi (2002), this meat is highly nutritious, high in digestible protein, low in fat and competes favourably with poultry egg and flesh in essential amino acids. Owing to these qualities, Nodu and Adesope (2002) grouped snails among the excellent sources of animal protein. Omole et al. (1998) also advocated that snail meat could be used as alternative source of animal protein because of its crude protein (18.28 %) content. Besides, Stievenant (1992) stated that snail has a highly palatable flesh of about 60 % crude protein on a dry matter basis and shell made up of calcium carbonate. Snail meat had been proved to be free of cholesterol (Odunaiya 1995) and is therefore always recommended for sufferers of cardiovascular and anaemic problems.

The domestication and hence rearing of snails is a new development in animal production and research in Nigeria (Akinnusi 1997 and Ibom 2009). Akinnusi (2000) also stated that snail as a micro-livestock has recently attracted attention of Nigerian agriculturists and farmers as an aftermath of the alarm raised by Food and Agriculture Organization on animal protein deficiency among Nigerians. Snail as a species has many advantages to receive considerable emphasis and be popular. Some of these advantages include high protein and energy level in human diet of snail meat, its medicinal value, its not a red meat, rapid turnover rate, short incubation period (14 30 days) of eggs, employment generation for the unemployed, source of income to the keepers, relatively wide acceptability, ready market for snail products owing to fewer social taboos and easy adaptability to various environment. Its shell can also be used in animal feed formulation as calcium source. Considering these advantages, snail production can play a significant role in fighting poverty and malnutrition among the teeming population.

Snail production is yet to attain the desired level of productivity in Nigeria due to none availability of desirable foundation stock and discrimination against certain ectotypes. The culprit of this discrimination is often times the white-skinned (albino) ectotype (Ibom 2009). Ibom et al. (2008) compared the morphological characteristics of eggs laid by two ectotypes (black-skinned and white-skinned) of Archachatina marginata. Besides, extensive snail research and extension services are still lacking due to the traditional emphasis on conventional animals. Snails are hermaphrodites but practice sexual reproduction and are choosy in their mating partners (Akinnusi 2004 and Ibom and Okon 2010). It is therefore imperative to further assess the possibility of mating between the black-skinned (BS) and white-skinned (WS) ectotypes of snail (A. marginata). There is need also to characterize the egg production ability of this inter-mating, with the aim of adapting their snailets to the traditional small scale system of animal production prevalent in Nigeria. This study will further affirm the findings of Ibom (2009), Okon et al. (2009) and Ibom and Okon (2010), that mating is possible between the black-skinned and white-skinned ectotypes of A. marginata. It will also debunk the argument in some quarters that the black-skinned ectotypes do not mate with the white-skinned (albino) ectotypes owing to the choosy nature of mating partners by land snails or differences in pigmentation and genetic constitution.

MATERIALS AND METHODS

The study was conducted at the Snailery Unit, Department of Animal Science Teaching and Research Farm, Cross River University of Technology, Obubra Campus. The description of the area and climate of Obubra were as prescribed elsewhere in Ibom et al. (2008) and Ibom (2009).

Forty mature snails, twenty each of the black-skinned (BS) and white-skinned (WS) or albino ectotypes with weight ranging from 51.19 81.34 g and 50.87 80.62 g respectively for the BS and WS ectotypes used for the study were purchased from a local market in Ikom, Cross River State. The snails which were managed in wooden cells kept under trees shade were allowed a stabilization period of thirty days. During this period, they were fed commercial layer mash before being introduced to the formulated diet in the last seven days. It is believed that fertilized eggs in mating that took place in their natural habitat were shed during the stabilization period.

After stabilization, the snails were allotted at random into four treatments on the basis of weight (50.87 51.19 g, 60.74 61.19 g, 70.64 71.32 g and 80.62 81.34 g) and each treatment replicated five times in the randomized complete block design. There were two snails to a cell in a natural mating (breeding) system of one BS ectotype to one WS ectotype ratio. Keeping two snails in a cell was to be sure that egg(s) obtained resulted from the mating of these two. The snails were left together in one cell for one week and separated for another one week for ease of identifying eggs laid by either ectotype. The snails were monitored for reproductive performance and two egg clutches collected from each of the snails in a cell during the months of May to July for evaluation.

Throughout the study period, the snails were fed on a mixed feeding regime of forage (pawpaw leaves) and formulated diet. The diet contained 24 % CP, 15 % Ca and 2650 Kcal/kg ME. It was formulated with the following ingredients; maize, soybean meal, fish meal, bone meal, wheat offal, oyster shell and vitamin/mineral premix. Feed and water were given ad libitum in shallow troughs throughout the study period.

Morphological characteristics (traits) measured on parent snails included initial body weight (g), shell length (mm), shell width (mm), aperture length (mm) and aperture width (mm), while those measured on eggs were egg weight (g), egg length (mm) and egg width (mm). The incubation period and percentage hatchability of eggs laid by these ectotypes were also determined. Correlated relationships between morphological traits measured on the parent snails and their eggs were estimated. ScoutTM Pro electronic scale with 0.01 g sensitivity was used to measure weight while Vernier Caliper was used to measure length and width of the snails' eggs.

Across groups data were analyzed using analysis of variance according to SAS (1999) software. Correlated relationships among traits were determined according to methods outlined by Falconer (1989) and Ibe (1998). Significant means were separated by Least Significant Difference of the same the SAS (1999) software.

RESULTS AND DISCUSSION

Table 1 shows the results of morphological characteristics of parent snail ectotypes (Black-skinned and White-skinned) and eggs obtained from their matings. The results on Table 1 showed that all the parent snail traits; body weight, shell length, shell width, mouth' length and mouth' width varied within and across the four body weight groups evaluated. However, the variations within groups (that is between the black-skinned (BS) and the white-skinned (WS) ectotypes) for body weight were not statistically different (P>0.05). The trend in non significant difference was also observed in other traits measured on the parent snails. The trend might mean that irrespective of ectotypes, a given weight range of Archachatina marginata snail breed under the same environmental conditions (management and feeding) do not express significant differences.

The clutch size varied within and across the four body weight groups studied (Table 1). The mean clutch sizes obtained in this study for the BS and WS snails respectively were 8.380.32 and 4.380.82 (group 1), 7.130.35 and 4.75 0.49 (group 11), 7.380.26 and 4.380.60 (group III) and 7.630.53 and 4.88 0.55 (group 1V). Mean clutch size values recorded in this study for the BS snails are in agreement with the mean value of 7.8 reported by Ibom et al. (2008) for the same ectotype. However, the mean clutch size values of this study for the WS snails are slightly lower than the 5.23 mean value reported by the same authors for WS ectotype. The WS ectotype mean clutch size values of this study agreed with Okon et al. (2010a) who reported 4.85 for first parity litter of the same ectotype. The values obtained in this study for BS ectotype are also in line with the values of 7, 8 and 8.5 reported by Awesu (1980), Reid (1989) and Amubode (1994) respectively. There was no significant difference (P>0.05) in clutch size between similar ectotypes in the four body weight groups studied. However, there were significant differences (P0.05), whereas they were significantly (P

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